feat(chess): preset-flexibility architecture — decouple HP, damage, piece-types, state, effects

Decouples five cross-cutting concerns from engine core so new presets
compose without special-casing:

- Piece attributes: CORE_PIECE_ATTRS + PresetDef.pieceAttributes;
  engine.effectivePieceAttrs unions them. HP is now preset-owned.
- Spawn pipeline: engine.spawnPiece() + onPieceSpawn hook replaces
  hand-rolled materialization. Queen-splits seeds HP via the hook,
  not via direct knowledge of piece-hp.
- Hook signatures: all hooks now take single context objects
  (LifecycleContext, MoveHookContext, CaptureHookContext, DamageHookContext,
  SelfCheckFilterContext, GameResultHookContext, PieceSpawnContext,
  BeforeMoveContext, TurnStartContext, DescribeMoveEffectContext).
- Piece-type registry: PIECE_TYPE_REGISTRY + core-piece-types.ts
  replaces hardcoded FIDE switch-tables in engine/check/checkmate/
  stalemate/Piece.tsx. Custom piece types plug in without engine edits.
- Preset-scoped state: engine.presetState<T>(id) backed by facts on
  PRESET_STATE_ENTITY. Auto-cleared on deactivate. capture-to-win
  migrated off GAME_ENTITY.Winner.
- Move log: engine.moveLog + MoveRecord + describeMoveEffect hook.
- Visual effects: engine.emitEffect/subscribeEffects + VisualEffect +
  VisualEffectLayer. Explosion, heal, poison renderers. No-op when
  no subscribers.
- Phase hooks: onBeforeMove (with cancel), onTurnStart. Scope-aware
  dispatch routes onDamage/onBeforeMove/onTurnStart by target/mover
  color.

All 5 production presets migrated. 4 prototype presets (Shield, Cannon,
Berserker, PawnStamina) in integration.test.ts exercise every hook.
Added test-utils.ts and PRESET-API.md for preset authors.

930 tests passing; bun run check clean.
This commit is contained in:
Joey Yakimowich-Payne 2026-04-18 16:26:17 -06:00
commit cc30545ced
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32 changed files with 3611 additions and 304 deletions

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# Preset Flexibility — Architecture Pass
## TL;DR
Nine architectural improvements plus two phase hooks that unblock the next generation of chess-variant presets without a single engine touch per preset.
**Core problems today**:
1. `PIECE_ATTRS` is hardcoded — new attribute-carrying presets (Shield, Armor, Stamina) leave zombie facts on death.
2. No piece-spawn primitive — `queen-splits` has a latent HP-coupling bug waiting for a mid-game activation order to trigger.
3. Piece types are a closed union — no Cannon, Amazon, Nightrider without editing core.
4. No visual effect bus — explosions/heals/poison ticks are silent.
5. No move log — history panels, PGN export, analysis tools all blocked.
6. Per-preset state is ad-hoc (global modules or game-entity facts); breaks concurrent games and save/load.
7. Hook signatures are positional — growing them breaks every implementer.
8. `onAfterMove`, `onDamage`, `onCheckGameResult` ignore scope; presets re-derive it.
9. Test harness pattern duplicated across every preset test file.
**Deliverable**: after this work, a preset can add a new piece type, a new piece attribute, new damage kinds, new visual effects, and new per-game state — all without changing a single line of engine/core code. Every existing preset continues to behave identically in isolation; new compositions (HP + any new damage source) work automatically.
**Phases**: 4 phases, 23 tasks, hard-gated by `bun run check` green + behavioral tests green between each.
---
## Context
### What Shipped Last
- Damage pipeline landed. `engine.dealDamage(target, amount, ctx)` is the canonical damage primitive; `piece-hp.onDamage` is the sole damage→death arbiter.
- `explosive-rook` + `piece-hp` now compose naturally (blast deals 1 HP each; pieces with HP>1 survive). The previous hard incompatibility was removed.
- `queen-splits` and `poisoned-squares` route captures/ticks through the pipeline.
- 889 unit tests pass, including 12 new damage-pipeline tests.
### What Still Couples Presets to Core
Audited the live code for every preset-visible engine surface. The remaining friction points:
- `packages/chess/src/rules/capture.ts:10` — `PIECE_ATTRS` is a frozen 5-element tuple. Adding an attribute requires editing this file.
- `packages/chess/src/presets/piece-hp.ts:77` — `const PIECE_ATTRS = [...]` duplicates the list. Another edit point.
- `packages/chess/src/presets/queen-splits.ts:60` + `:84-97` — owns a `PIECE_ATTRS` copy plus a private `spawnPiece` helper. Spawned pieces aren't passed through any hook — if `piece-hp` activates AFTER queen-splits spawns pieces, those pieces have no `Hp`.
- `packages/chess/src/schema.ts:PieceType` — fixed union of 6 types. Hardcoded in `PIECE_MOVE_GETTERS` (`engine.ts:61`), `ATTACK_PROBES` (`check.ts:68`), `MOVE_GETTERS` (`checkmate.ts:44`), `stalemate.ts`, plus UI asset maps. Five synchronized tables.
- `packages/chess/src/engine.ts:applyMove` — emits nothing. Clients reconstruct history from fact diffs. No per-move summary, no notation, no event stream.
- `packages/chess/src/presets/capture-to-win.ts:46` + others — use `GAME_ENTITY` facts as ad-hoc state storage. Mixed with real game-level facts (`Turn`, `EnPassantTarget`, `HalfmoveClock`). Collision surface grows with each preset.
- `packages/chess/src/presets/registry.ts` — every hook is `(engine, ...positional args) => Result | void`. Every signature change is a breaking change to every preset.
- `packages/chess/src/presets/*.test.ts` — `pieceAt`, `hpOf`, `typeOf`, `clearRank` are copy-pasted across at least 4 files.
### Out of Scope
- Any new **presets** (piece types, rules). This plan is pure infrastructure.
- Save-file forward compatibility for saved games that predate this refactor. Autosave is dev-only; we can ship a one-line version bump + clear stale saves.
- Server-protocol version bump beyond what structured move emissions require. We keep protocol v1 and add new optional fields.
- UI redesigns beyond the minimum needed to render new visual effects.
---
## Work Objectives
### Core Objective
Decouple every preset-reachable engine surface so the `PresetDef` interface + registry is the ONLY thing a new preset touches.
### Concrete Deliverables
1. **Dynamic piece-attribute registry** — presets declare their attrs; retract / damage / save paths consult the union.
2. **`spawnPiece` primitive** + **`onPieceSpawn` hook** — single entry point for creating pieces; every active preset gets a chance to tag new entities.
3. **Custom piece-type registry** — presets register `(id, moveGenerator, attackProbe, assets)`; engine + UI look them up dynamically.
4. **Per-preset state bag** — `engine.presetState<T>(id)` with typed, engine-scoped, serialization-included state.
5. **Visual effect bus** — `engine.emitEffect({...})` + React subscriber; explosions/heals/poison ticks animate.
6. **Structured move log** — `applyMove` populates `MoveRecord`; `engine.moveLog` is the authoritative history stream.
7. **Hook-context objects** — all hooks take a single growable context object; future fields are additive.
8. **Scope-aware hook dispatch** — engine skips hooks whose scope doesn't cover the current color.
9. **Test harness utilities** — shared `test-utils.ts` for `engineWithPosition`, `placePiece`, `clearBoard`, etc.
10. **Phase hooks** — `onBeforeMove` (pre-validation, pre-mutation) and `onTurnStart` (after turn flip, before legal moves are regenerated) for cooldown/regen/resource-tick presets.
11. **Tests** — each new API gets unit tests; one integration test verifies a hypothetical "Shield" preset can be written from the registry alone without engine edits.
### Definition of Done
- `bun run check` green (typecheck + lint + 900+ tests).
- Every existing preset still works with no behavioral change in isolation (regression).
- The three prototype presets built in test code to exercise the new surfaces (Cannon piece type, Shield attribute, DamageCooldown state) all work.
- No references to literal `["PieceType", "Color", "Position", "HasMoved", "Hp"]` outside `engine.ts` / `registry.ts` / `schema.ts`.
- New `packages/chess/docs/PRESET-API.md` documenting the complete extension surface.
### Must Have
- All 9 items from the architecture review + 2 phase hooks.
- Backward-compatible hook signatures via the context-object refactor (old positional signatures accepted as a deprecation layer, removed in a single sweep after all in-tree callers migrate).
- Zero behavior regressions for existing presets (piece-hp, explosive-rook, queen-splits, king-heals, poisoned-squares, capture-to-win, last-piece-standing, all geometry presets).
### Must NOT Have (Guardrails)
- No event-bus abstraction for cross-preset communication. Presets talk to the ENGINE, not each other. If two presets need to coordinate, it's a design smell requiring review.
- No topological sort / priority system for preset ordering. Registration order + first-consumer-wins is sufficient. If ordering matters for a future pair, that's a design conversation, not a generic engine feature.
- No preset-defined alternative move validators. Move generation stays in `rules/`; presets *contribute extra moves* or *filter existing moves* via `getExtraMoves` / `filterMoves`, not replace the validator.
- No runtime piece-type registration through the UI / save files. Piece types are dev-authored TS modules that `register` at module-load time. User-uploaded code remains forbidden (RCE vector).
- No breaking changes to the WebSocket protocol shape. New optional fields only.
---
## Verification Strategy
### Test Decision
**TDD for each engine API surface**. Unit tests written alongside (or before) each primitive. Integration-style tests for composite behaviors (e.g., "HP + custom-type Cannon composes correctly").
### Regression Net
The existing 889 tests cover every shipped preset. They stay green through the entire refactor. `bun run check` runs at the end of every phase.
### Integration scenarios (run in the final verification wave)
1. **Shield attribute, from nothing**: Write a `piece-shield` preset using only public APIs — declares `pieceAttributes: ["Shield"]`, seeds on `onActivate`, absorbs damage via `onDamage` with higher priority than HP. Confirm retraction cleans up `Shield` facts (dynamic `PIECE_ATTRS`).
2. **Cannon piece type**: Write a preset that spawns a Cannon on d1 (Chinese-chess semantics — moves like a rook, captures only by jumping one piece). Register the piece type via the new API. Confirm UI renders it; move generation works; it's a legal target for checks; it saves/loads.
3. **Per-preset state survival**: Write a `berserker-cooldown` preset that uses `engine.presetState` to track last-rage-turn per piece. Save → restore → state is preserved. Activate → deactivate → state is cleared.
4. **Visual effect smoke test**: Playwright test — enable explosive-rook, trigger a capture, assert a DOM element with `data-effect="explosion"` appears briefly on the target square.
5. **Phase hook cooldown preset**: Write a `pawn-stamina` preset that uses `onTurnStart` to regenerate a `Stamina` attribute up to 2. Consuming it via `onBeforeMove` when pawns push. Proves the new phase hooks fire at the right times.
### QA Policy
- After every task: run focused tests for the touched file(s).
- After every phase: `bun run check` must be clean.
- After the full plan: Playwright smoke (`packages/chess/e2e/*.spec.ts --workers=1`), verify the 3 existing E2E specs + any new visual-effect one.
---
## Execution Strategy
### Phase Structure
Four phases, strictly sequential. Within each phase, tasks with no mutual dependency can run in parallel.
- **Phase A — Foundations**: dynamic attributes, spawn primitive, context objects. Touches `engine.ts` + `registry.ts` + per-preset cleanup. Everything else in this plan builds on this.
- **Phase B — State & Events**: per-preset state bag, move log, visual effect bus. These add emission points to `applyMove`; need A's context objects to be clean.
- **Phase C — Extension Surfaces**: custom piece types, scope-aware dispatch, phase hooks. New hooks declared in PresetDef; engine dispatches them; prototype presets in tests verify they fire.
- **Phase D — Developer Experience**: test harness, docs, final integration scenarios.
### Parallel Execution Waves
Phase A (serial foundation, then parallel cleanup):
Wave A.1 (sequential — core APIs):
A.1 PIECE_ATTRS → dynamic registry (engine + capture.ts)
A.2 engine.spawnPiece + onPieceSpawn hook
A.3 Hook context objects (HookContext, MoveContext, DamageContext renames)
Wave A.2 (parallel — cleanup existing presets using A.1-A.3):
A.4 piece-hp: migrate to declared attrs + context args
A.5 queen-splits: migrate to engine.spawnPiece, drop PIECE_ATTRS copy
A.6 explosive-rook: drop retractEntity helper, use dynamic PIECE_ATTRS
GATE: bun run check; all 889 existing tests green.
Phase B (parallel — state / events / log):
Wave B.1 (parallel):
B.1 engine.presetState<T>() + session-backed storage
B.2 MoveRecord + engine.moveLog + applyMove emission
B.3 engine.emitEffect() + EffectStream subscriber API
B.4 UI: VisualEffectLayer reads the stream, renders with Motion
GATE: bun run check; 3 new unit test suites (state, log, effects) pass.
Phase C (parallel except C.1 which gates C.2-C.3):
Wave C.1 (sequential foundation):
C.1 PieceTypeRegistry (engine + UI asset lookup)
Wave C.2 (parallel, depends on C.1):
C.2 registerPieceType API + engine move/attack tables become dynamic
C.3 Scope-aware hook dispatch (onAfterMove/onDamage/onCheckGameResult/new phase hooks)
C.4 onBeforeMove + onTurnStart phase hooks
C.5 Server-protocol: piece-type registry echoed on game.state
GATE: bun run check; Cannon prototype preset works end-to-end.
Phase D:
Wave D.1 (parallel):
D.1 packages/chess/src/presets/test-utils.ts + migration of existing tests
D.2 packages/chess/docs/PRESET-API.md (complete extension surface)
D.3 Integration scenarios (Shield / Cannon / Berserker / Stamina prototypes in test code)
FINAL GATE: bun run check + Playwright E2E + all integration scenarios green.
---
## TODOs
### Phase A — Foundations
#### A.1 — Dynamic piece-attribute registry
**Where**: `packages/chess/src/rules/capture.ts`, `packages/chess/src/engine.ts`, `packages/chess/src/presets/registry.ts`
**Why**: Preset-declared attributes (Shield, Stamina, Armor) must be retracted on death / serialized on save. Hardcoded list = silent bug.
**How**:
1. Rename existing `PIECE_ATTRS` to `CORE_PIECE_ATTRS` in `capture.ts`; keep it as the FIDE minimum.
2. In `registry.ts` add `readonly pieceAttributes?: readonly AttrKey[]` to `PresetDef`.
3. In `engine.ts` add a private computed getter `get effectivePieceAttrs(): readonly AttrKey[]` that returns `CORE_PIECE_ATTRS ∪ union(active preset pieceAttributes)`.
4. Replace every in-tree reference to literal `["PieceType", "Color", "Position", "HasMoved", "Hp"]` with `engine.effectivePieceAttrs` (or `CORE_PIECE_ATTRS` for pure-function contexts).
5. `dealDamage`'s default retract path uses the dynamic list. Same for piece-hp's lethal retract path. Same for queen-splits' queen retract.
6. `Hp` attribute moves OFF `CORE_PIECE_ATTRS` — it's owned by `piece-hp` via `pieceAttributes: ["Hp"]`.
**Expected result**: `PIECE_ATTRS` no longer appears as a literal in any preset. Adding a new attribute-carrying preset requires only a `pieceAttributes` declaration. Existing HP tests continue to pass — `Hp` is cleaned up when pieces die because `piece-hp` contributes it to the dynamic list.
**Tests**: Unit — a test preset that declares `pieceAttributes: ["TestMark"]`, seeds it on onActivate, then gets retracted on piece death. Verify no `TestMark` fact remains.
---
#### A.2 — `engine.spawnPiece()` primitive + `onPieceSpawn` hook
**Where**: `packages/chess/src/engine.ts`, `packages/chess/src/presets/registry.ts`, `packages/chess/src/presets/queen-splits.ts`
**Why**: `queen-splits` has a latent bug — pieces it spawns don't get `Hp` seeded if HP was activated *after* queen-splits started having reason to spawn. Plus future presets (promotion variants, summoning, phoenix) need the same thing.
**How**:
1. Add to `PresetDef`: `readonly onPieceSpawn?: (ctx: PieceSpawnContext) => void;`. `PieceSpawnContext = { engine, pieceId, type, color, square, reason: "promotion" | "fission" | "summon" | (string & {}) }`.
2. Add `engine.spawnPiece(type, color, square, opts?: { reason?: string; hasMoved?: boolean }): EntityId`. Creates entity, inserts CORE attrs, then iterates `activePresets.list()` calling each `onPieceSpawn`. Returns the new id.
3. `piece-hp` implements `onPieceSpawn` → `engine.session.insert(id, "Hp", DEFAULT_HP)`.
4. `queen-splits` deletes its private `spawnPiece` helper, calls `engine.spawnPiece("rook", color, square, { reason: "fission" })` twice.
5. (Future) promotion rule in `rules/promotion.ts` migrates to `spawnPiece` — tracked as stretch for this task, do only if trivial.
**Expected result**: Activating queen-splits in any order with piece-hp produces fission-spawned pieces with `Hp = 2` as expected. No more "idempotent onActivate" duct tape.
**Tests**: Unit — activate queen-splits, then piece-hp, then trigger fission. Verify spawned rook + bishop both have `Hp = 2`. Activate in reverse order. Verify same.
---
#### A.3 — Hook context objects
**Where**: `packages/chess/src/presets/registry.ts`, `packages/chess/src/engine.ts`, all `packages/chess/src/presets/*.ts`
**Why**: Positional signatures break every preset when we add a field. Context objects are growable.
**How**:
1. Define per-hook context types in `registry.ts`:
```ts
interface HookContext { readonly engine: ChessEngine; }
interface MoveHookContext extends HookContext { readonly moverColor: PieceColor; readonly move: MoveRecord; /* added in B.2 */ }
interface DamageHookContext extends HookContext {
readonly target: EntityId;
readonly amount: number;
readonly kind: string;
readonly attacker?: EntityId;
}
interface PieceSpawnContext extends HookContext {
readonly pieceId: EntityId;
readonly type: PieceType;
readonly color: PieceColor;
readonly square: Square;
readonly reason: string;
}
// etc for every hook
```
2. Migrate every `PresetDef` hook signature to take a single context object.
3. Migrate every preset implementation. Engine dispatchers construct context objects and pass them.
4. Temporarily keep positional form for `onDamage` and `onBeforeCapture` accepted via an adapter, emit a `console.warn` in dev-mode. Remove the adapter in the same PR once all callers migrate (since this is all in-tree).
**Expected result**: Future hook additions are purely additive — `MoveHookContext` gains a `lastCaptureSquare?: Square` field, zero presets break.
**Tests**: Migrate existing hook tests to new signature; add a single assertion that unknown context fields are silently ignored by presets that don't read them (typechecker covers this).
---
#### A.4 — Migrate `piece-hp` to declared attrs + context args
Depends on A.1, A.2, A.3.
**Why**: Prove the new pattern works on the most-used preset first.
**How**:
- Add `pieceAttributes: ["Hp"]` to the PresetDef.
- Drop the in-file `PIECE_ATTRS` duplicate.
- Hook signatures converted to context args.
- `onPieceSpawn` implementation added (seeds Hp=2 on new entities).
- `onActivate` becomes slightly simpler (no need to iterate and check; pieces spawned after activation auto-get Hp via `onPieceSpawn`).
**Tests**: Existing piece-hp tests + fleshed-presets tests stay green.
---
#### A.5 — Migrate `queen-splits` to `engine.spawnPiece`
Depends on A.2.
**Why**: Removes queen-splits's private spawn helper; removes the dead `// ... relies on piece-hp onActivate idempotence` comment.
**How**: Replace the two `spawnPiece(session, ...)` calls with `engine.spawnPiece(...)`. Delete the private helper. Drop the `PIECE_ATTRS` constant.
**Tests**: Existing queen-splits tests stay green. Add one explicit test for the "HP activated after queen-splits mid-game" scenario.
---
#### A.6 — Migrate `explosive-rook`, `poisoned-squares` to dynamic attrs
Depends on A.1.
**Why**: These carry their own retraction helpers.
**How**: Replace local `PIECE_ATTRS` with `engine.effectivePieceAttrs` where they retract directly (explosive-rook's fallback path if it's not using dealDamage for some future reason; poisoned-squares already uses dealDamage so may need zero edits — audit). Keep behaviour identical.
**Tests**: Existing tests stay green.
**GATE A**: `bun run check` green. Every existing test passes.
---
### Phase B — State & Events
#### B.1 — `engine.presetState<T>(id)`
**Where**: `packages/chess/src/engine.ts`, `packages/chess/src/schema.ts`
**Why**: Per-game, per-preset state with zero collision, included in save-state.
**How**:
1. Define `PRESET_STATE_ENTITY` symbol in `schema.ts` (new entity id, below `GAME_ENTITY`).
2. `engine.presetState<T>(presetId: string): T` returns a typed Proxy backed by session facts of the form `(PRESET_STATE_ENTITY, `${presetId}::${key}`, value)`.
3. `get` reads the fact; `set` inserts/retracts; `delete` retracts.
4. On preset deactivate, engine retracts every fact with attr matching `${presetId}::*`.
5. Fact serialization already covers these — save/load works automatically.
**Tests**:
- Write + read + save + load round-trip.
- Activate → write state → deactivate → state cleared → reactivate → empty.
- Two concurrent engines with the same preset ID have independent state (server concurrency).
**Expected result**: Migrate `capture-to-win`'s `Winner` fact from `GAME_ENTITY` to its preset-state bag as a proof point.
---
#### B.2 — `MoveRecord` + `engine.moveLog` + `applyMove` emission
**Where**: `packages/chess/src/engine.ts`, `packages/chess/src/presets/registry.ts` (new hook `describeMoveEffect`)
**Why**: History UI, PGN export, replay — all need a per-move summary. Currently requires diffing facts.
**How**:
1. Add `MoveRecord` interface in `engine.ts`: `{ from, to, moverColor, movingType, capturedId, capturedType, isCheck, isCheckmate, isEnPassant, isCastling, promotion, presetEffects, timestamp }`.
2. Private `this.#moveLog: MoveRecord[] = []`; public getter.
3. Populate inside `applyMove` at the very end, before return.
4. Optional hook on `PresetDef`: `describeMoveEffect?(ctx): { presetId: string; summary: string } | void`. Engine iterates, collects non-void returns into `presetEffects`.
5. Update `MoveHookContext` (from A.3) to carry the MoveRecord being built (or the finalized one, depending on hook timing).
**Tests**:
- Move sequence produces correct log entries.
- Capture is logged with `capturedType`.
- Checkmate is logged with `isCheckmate: true`.
- `describeMoveEffect` is called and results show up in `presetEffects`.
---
#### B.3 — `engine.emitEffect()` + effect stream API
**Where**: `packages/chess/src/engine.ts`, `packages/chess/src/ui/VisualEffectLayer.tsx` (new)
**Why**: Visual feedback. Currently explosions, heals, poison ticks happen silently.
**How**:
1. `VisualEffect` interface: `{ kind: string; square: Square | null; ttl: number; data?: Record<string, unknown> }`.
2. `engine.emitEffect(effect: VisualEffect)` pushes onto an internal ring buffer; notifies subscribers.
3. `engine.subscribeEffects(handler): Unsubscribe`.
4. UI layer mounts a fixed-position overlay inside `Board.tsx`; subscribes once; renders effects with Motion (fade/scale/slide based on kind).
5. Presets call it directly: `explosive-rook` emits `{ kind: "explosion", square: targetPos, ttl: 600 }`; `king-heals` emits `{ kind: "heal", square: kingSq, ttl: 400 }`; `poisoned-squares` emits per-tick `{ kind: "poison", square, ttl: 250 }`.
**Tests**: Unit — emit + subscribe; unit — TTL cleanup; Playwright — trigger explosive-rook capture, assert `[data-effect="explosion"]` briefly present.
---
#### B.4 — UI: VisualEffectLayer integration
Depends on B.3.
**Where**: `packages/chess/src/ui/Board.tsx`, `packages/chess/src/ui/VisualEffectLayer.tsx` (new)
**Why**: Ship B.3 as a visible feature.
**How**: Mount layer inside board viewport. Per-kind effect component (ExplosionBurst, HealPulse, PoisonBubble). Use Motion's `AnimatePresence` for entry/exit; auto-remove after TTL.
**Tests**: Playwright smoke (see B.3).
**GATE B**: `bun run check` green. Visual smoke test green. Capture-to-win's Winner fact has migrated to presetState.
---
### Phase C — Extension Surfaces
#### C.1 — PieceTypeRegistry (core)
**Where**: `packages/chess/src/presets/piece-type-registry.ts` (new), `packages/chess/src/schema.ts`
**Why**: Foundation for custom piece types.
**How**:
1. New class `PieceTypeRegistry` with methods `register(def: PieceTypeDef)`, `get(id)`, `getAll()`, `has(id)`.
2. `PieceTypeDef { id, displayName, moveGenerator, attackProbe, assets: { whiteSvg, blackSvg } }`.
3. `PieceType` becomes `string` (not a fixed union). Runtime validation via registry membership.
4. Built-in types (pawn/knight/etc) register at module load via a `core-piece-types.ts` that's imported from the barrel.
**Tests**: Unit — register new type, iterate, lookup by id.
---
#### C.2 — Engine + UI consume PieceTypeRegistry
Depends on C.1.
**Where**: `packages/chess/src/engine.ts`, `packages/chess/src/rules/check.ts`, `packages/chess/src/rules/checkmate.ts`, `packages/chess/src/ui/Piece.tsx`, `packages/chess/src/assets/pieces/index.ts`
**Why**: Swap the five hardcoded dispatch tables (`PIECE_MOVE_GETTERS`, `ATTACK_PROBES`, `MOVE_GETTERS`, asset map, stalemate's table) for registry lookups.
**How**:
1. `engine.getLegalMovesForPiece(id)` resolves move generator via registry.
2. `isSquareAttacked` + `isCheckmate` + `isStalemate` do the same.
3. UI `<Piece>` looks up SVG assets from registry's `assets` field.
4. Starting-position fact generator stays as-is (still uses hardcoded 32-piece FIDE layout).
**Tests**: Unit — register a Cannon piece type; place a Cannon entity; verify it appears as a legal attacker in check detection; verify the UI renders its asset (Playwright).
---
#### C.3 — Scope-aware hook dispatch
**Where**: `packages/chess/src/engine.ts`, `packages/chess/src/presets/active-set.ts`
**Why**: Reduces per-preset scope boilerplate; makes scope semantics consistent.
**How**:
1. Every hook that has a "for whom" semantics gets a `scopeFilter: PieceColor` context field (set by the engine based on who's moving / whose piece is taking damage / etc).
2. `ActivePresetSet` gains `getForColorAndHook(color, hookName)` returning only presets whose scope covers `color`.
3. `onAfterMove` fires only for presets scoped to mover color (+ `both` which is default). Same for `onDamage` based on target's color.
4. `onCheckGameResult` fires for all (no scope — terminal state is global).
**Tests**: Test preset scoped `white`; apply a black move; verify preset's onAfterMove did NOT fire. Apply a white move; verify it DID.
---
#### C.4 — Phase hooks: `onBeforeMove` + `onTurnStart`
**Where**: `packages/chess/src/presets/registry.ts`, `packages/chess/src/engine.ts`
**Why**: Enable cooldown / stamina / resource-regen presets without shoehorning into `onAfterMove`.
**How**:
1. `onBeforeMove(ctx: BeforeMoveContext): { cancel?: boolean; reason?: string } | void` fires after move legality is confirmed but before any state mutation. Returning `{cancel: true}` aborts the move — engine treats as illegal and calls `toast.error` with `ctx.reason`. (This is a strong capability; fencing it with `cancel` vs a generic `consume` because we want explicit semantics.)
2. `onTurnStart(ctx: TurnStartContext): void` fires after the turn has flipped, before the new side-to-move's legal moves are computed. Good place for "regenerate stamina", "decrement cooldowns", "re-bless pieces on altar squares".
3. Engine dispatches both at the right points in `applyMove`.
**Tests**: Stamina-regen preset in test fixture — set Stamina to 0; run a turn; verify `onTurnStart` regenerated it to 1; run a pawn push; verify `onBeforeMove` consumes 1 stamina; if Stamina < cost, preset cancels move.
---
#### C.5 — Server-protocol: piece-type registry echoed on `game.state`
**Where**: `packages/server/src/broadcast.ts`, `packages/server/src/protocol.ts`, `packages/chess/src/net/types.ts`
**Why**: Clients that join mid-game need the piece-type registry to render a custom type correctly. Currently not an issue (all types hardcoded) but will be as soon as C.2 ships.
**How**:
1. Add optional `pieceTypes?: PieceTypeManifest[]` to `GameStatePayload`.
2. Server computes from `PRESET_REGISTRY` at room creation; sends on `room.joined` + `game.state`.
3. Client compares manifest to its local registry; if mismatch, shows a connection error ("server uses unknown piece types").
4. Protocol version stays `v: 1` — new optional field.
**Tests**: Unit — server sends manifest; client parses; mismatch rejected cleanly.
**GATE C**: `bun run check` green. Cannon piece type end-to-end test works (Playwright): create room with cannon preset, place cannon, move it, see it on both clients.
---
### Phase D — Developer Experience
#### D.1 — `packages/chess/src/presets/test-utils.ts`
**Where**: new file.
**Why**: Four preset test files copy-paste the same helpers.
**How**:
1. Export `pieceAt(engine, square)`, `hpOf(engine, id)`, `typeOf(engine, id)`, `exists(engine, id)`.
2. Export `clearBoard(engine, { preserveKings?: boolean })`.
3. Export `placePiece(engine, type, color, square, opts?): EntityId`.
4. Export `engineWithPosition(partial: Record<Square, { type, color }>): ChessEngine`.
5. Migrate the 4 existing preset test files to import from here; delete local copies.
**Tests**: `test-utils.test.ts` — cover each helper's happy path.
---
#### D.2 — `packages/chess/docs/PRESET-API.md`
**Where**: new file.
**Why**: The `PresetDef` interface is now the public API. Needs reference-quality docs.
**How**: Structured reference doc:
- Overview + philosophy (engine-as-minimal-core, presets-as-composition)
- `PresetDef` interface with every field + hook documented
- Hook firing order (chronology within an applyMove)
- Context objects — type reference for every one
- Piece attribute registration
- Piece type registration
- Preset state bag usage
- Effect bus usage
- Scope semantics
- Phase hooks with cooldown/regen examples
- "Your first custom preset" walkthrough — builds the Shield preset from scratch in ~50 lines
**Tests**: Linked from `packages/chess/README.md`. Manual proofread.
---
#### D.3 — Integration scenarios (prototype presets in tests)
**Where**: `packages/chess/src/presets/integration.test.ts` (new).
**Why**: Proves the APIs are sufficient end-to-end. Each scenario builds a plausible preset using ONLY registry-level APIs.
**How**: Four scenarios described in Verification Strategy above, each as its own `describe` block.
1. Shield attribute preset.
2. Cannon piece-type preset.
3. Berserker cooldown (presetState).
4. Pawn stamina (phase hooks).
Each prototype preset lives in-file; they're test fixtures, not shipped. They validate that a third-party preset author could accomplish the same.
**Tests**: The scenarios themselves ARE the tests.
**FINAL GATE**:
- `bun run check` green (target ~920 tests).
- Playwright E2E green.
- `packages/chess/docs/PRESET-API.md` exists and mentions every new API.
- Zero hardcoded `PIECE_ATTRS` / `PIECE_MOVE_GETTERS` / `ATTACK_PROBES` literals outside engine/registry/schema.
---
## Commit Strategy
One commit per task (23 commits). Each:
- Body explains root cause + fix + impact.
- References the task id (e.g., `A.2: engine.spawnPiece primitive`).
- Pre-commit hook runs `bun run check` — must be green.
Phase boundaries get a merge-commit summary with an updated progress checklist in the PR description.
No batch commits. No squashes. Easy bisect.
---
## Success Criteria
### Objective
- A new preset that declares a new piece attribute, a new piece type, uses per-preset state, emits visual effects, and participates in scope-aware hooks can be written entirely within `packages/chess/src/presets/` — zero edits to anything under `packages/chess/src/engine.ts`, `packages/chess/src/rules/`, or `packages/chess/src/ui/` (other than `VisualEffectLayer`'s per-kind component, which is acceptable — new visual styles naturally live with the renderer).
- All existing presets behave identically in isolation.
- All existing E2E flows pass.
### Verification Commands
```bash
# From repo root
bun run check # typecheck + lint + unit tests
bun x playwright test packages/chess/e2e/ --workers=1
# Spot-checks
grep -rn '\["PieceType", "Color"' packages/chess/src/ | wc -l # expect 0 outside engine.ts / registry.ts
grep -rn "const PIECE_MOVE_GETTERS" packages/chess/src/ | wc -l # expect 1 (engine.ts) or 0 if fully dynamic
```
### Stretch (not required)
- Migrate `capture-to-win.Winner` facts from `GAME_ENTITY` to `presetState`.
- Migrate `rules/promotion.ts` to use `engine.spawnPiece`.
- Server broadcasts visual effects on each delta so clients stay in sync.
---
## Risk Log
| Risk | Likelihood | Mitigation |
|---|---|---|
| Dynamic `PIECE_ATTRS` breaks serialization of saved games | Medium | Autosave is dev-only; bump save-version; clear old on mismatch. |
| Piece-type runtime string-union relaxation causes implicit `any` in exhaustiveness checks | Medium | Add `satisfies` assertions at registry edges; lint rule for `PieceType === "king"` comparisons |
| Effect bus leaks memory (subscribers never unsubscribe) | Low | `subscribeEffects` returns `Unsubscribe`; `Board` unmounts cleanly; add dev-mode warning on > 20 active subscribers. |
| `onBeforeMove.cancel` misused to silently break chess | Medium | Require `reason: string` when cancelling; surface via toast; document as "use sparingly". |
| Protocol changes cause client/server version drift | Low | New fields are optional; existing clients ignore; piece-type manifest check is advisory only (warn, don't disconnect) in first release. |
| Context-object migration misses a preset and drops hook | Low | Typechecker enforces; grep for bare `onDamage:` in every preset file as final sweep. |
---
## Post-Landing Backlog (not in this plan)
- `onPieceRetract` hook — symmetric to `onPieceSpawn`, fires when a piece dies. Needed for "death rattle" presets (e.g., a piece explodes on death). Defer until a concrete preset wants it.
- Undo/redo for moves — requires `MoveRecord` (B.2) as prerequisite; currently implemented as full state snapshots, which the MoveRecord stream can replace.
- Preset-authored UI panels — e.g., a Stamina-bar side panel. Needs a standard extension slot in `GameView`. Low priority.
- Server-side preset validation DSL — presets currently live in `packages/chess`; server imports the same registry. If presets ever become user-authored (disallowed in v1), server needs a validation/sandbox layer.

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@ -0,0 +1,426 @@
# Preset API Reference
This document is the contract between the chess engine core and preset authors. Every extension point is listed here. If a capability you need isn't in this doc, it either isn't supported or hasn't landed yet.
**Audience**: developers adding new presets (either in-tree in `packages/chess/src/presets/` or as an external package that imports `@paratype/chess`).
**Philosophy**: the engine is a FIDE-minimum chess runtime with a compositional plugin surface. New mechanics — HP, custom pieces, visual effects, move history, resource tracking — attach via registries and hooks. Engine core should stay stable; extensions stay additive.
---
## Architecture at a glance
```
┌──────────────────┐ declares attrs, registers hooks
│ PresetDef │──────────┐
└──────────────────┘ │
▼
┌────────────────────────────────────────────────────┐
│ PRESET_REGISTRY │
│ • getAll() / get(id) │
└────────────────────────────────────────────────────┘
│
▼
┌──────────────────┐ applyMove / dealDamage / spawnPiece / emitEffect
│ ChessEngine │──┬───────────────────────────────┐
│ │ │ PIECE_TYPE_REGISTRY │
│ • session │ │ moveGenerator / attackProbe │
│ • moveLog │ │ assets │
│ • activePresets │ └───────────────────────────────┘
│ • presetState │
│ • emitEffect │
└──────────────────┘
```
---
## Writing a preset
Minimal preset — registers itself at module load via a side-effect import. Consumers add an import line in `packages/chess/src/presets/index.ts`.
```ts
import { PRESET_REGISTRY } from "./registry.js";
PRESET_REGISTRY.register({
id: "my-preset",
name: "My Preset",
description: "What this preset does in one sentence.",
incompatibleWith: [],
requires: [],
// ... hooks below
});
```
### Required fields
- `id: string` — stable identifier. Used for UI toggles, persistence, `engine.presetState`, hook dispatch order. Cannot be renamed without breaking saved games.
- `name: string` — display name for UI. Can change freely.
- `description: string` — one-line explainer shown in the rules drawer. Include variant-defining details ("captures deal 1 damage instead of killing").
- `incompatibleWith: string[]` — preset ids that must NOT be active under overlapping scope. Mutual — if A declares B incompatible, B must declare A too.
- `requires: string[]` — preset ids that MUST be active under overlapping scope. Examples: `king-heals` requires `piece-hp`.
### Optional: declared attributes
```ts
pieceAttributes: ["Shield"],
```
When your preset owns a piece-level attribute (HP, Shield, Stamina, Mana, Armor), declare it here. The engine unions `pieceAttributes` from every active preset into `engine.effectivePieceAttrs`. That list drives:
- The default damage-retract path (dead pieces lose all effective attrs).
- `queen-splits`'s attacker retraction during fission.
- Save-state serialization (all facts captured, including preset-declared attrs).
The attr MUST be declared in `ChessAttrMap` (via `declare module "../schema"` augmentation or by editing `schema.ts` directly). Adding a brand-new fact-type requires one schema edit + one preset edit.
---
## Hook reference
Hooks take a single context object (rather than positional args) so new fields are additive. All hooks are optional — implement only what your preset needs.
### Lifecycle
#### `onActivate(ctx: LifecycleContext)`
Fires when the preset transitions inactive → active. Use for:
- Seeding initial state (e.g. `Hp=2` on every existing piece).
- Mutating the session to reflect the preset's requirements.
```ts
onActivate({ engine }) {
for (const id of piecesOnBoard(engine)) {
engine.session.insert(id, "Hp", 2);
}
}
```
#### `onDeactivate(ctx: LifecycleContext)`
Symmetric cleanup. Fires when:
- User toggles preset off via the UI.
- Turn-timer expires (`turnsRemaining: 0`).
- Server issues `setPresets` that excludes this preset.
Retract anything `onActivate` inserted. Preset-state is cleared automatically AFTER this hook returns.
```ts
onDeactivate({ engine }) {
for (const id of piecesOnBoard(engine)) {
if (engine.session.contains(id, "Hp")) {
engine.session.retract(id, "Hp");
}
}
}
```
### Movement
#### `getExtraMoves(engine, pieceId): LegalMove[]`
Contribute additional legal moves for a specific piece. Used by wrap-board, knights-leap-twice, etc. NOT a context-object hook because it's called in a tight loop per piece per legal-move query — positional args are the perf-friendly choice.
#### `filterMoves(moves, engine, pieceId): LegalMove[]`
Remove or modify moves from the aggregated list. Used by knight-immunity (filters captures of knights).
### Damage
#### `onDamage(ctx: DamageHookContext): DamageHookResult | void`
The damage pipeline. Called by `engine.dealDamage(target, amount, ctx)`. First preset to return `{ consume: true, died }` wins — further presets are not consulted.
```ts
onDamage({ engine, target, amount, kind }) {
if (!engine.session.contains(target, "Hp")) return undefined;
const current = engine.session.get(target, "Hp") as number;
const next = current - amount;
if (next > 0) {
engine.session.insert(target, "Hp", next);
return { consume: true, died: false };
}
// Lethal — retract all effective attrs and report death.
for (const attr of engine.effectivePieceAttrs) {
if (engine.session.contains(target, attr)) engine.session.retract(target, attr);
}
return { consume: true, died: true };
}
```
Scope-aware: only fires for presets whose scope covers the target's color. A `scope=white` preset won't absorb damage on black pieces.
**Damage kinds** (extend as needed): `"capture"` (default from applyMove), `"explosion"` (explosive-rook), `"poison"` (poisoned-squares). Arbitrary strings allowed — document what YOUR preset emits.
### Capture
#### `onBeforeCapture(ctx: CaptureHookContext): CaptureHookResult | void`
Fires BEFORE the engine resolves a capture. Return `{ consume: true }` to REPLACE the default capture mechanic entirely — queen-splits fission, explosive-rook AoE, capture-to-win winner-recording. The consuming preset owns ALL post-capture behavior, including whether the attacker moves.
Unconsumed captures fall through to `engine.dealDamage` with `kind: "capture"`.
### Spawn
#### `onPieceSpawn(ctx: PieceSpawnContext)`
Fires when `engine.spawnPiece()` creates a new entity. Every active preset gets a chance to tag the piece (seed Hp, mark Shield, add custom attrs). Runs AFTER core attrs are inserted.
```ts
onPieceSpawn({ engine, pieceId }) {
engine.session.insert(pieceId, "Hp", DEFAULT_HP);
}
```
### Phase hooks
#### `onBeforeMove(ctx: BeforeMoveContext): BeforeMoveResult | void`
Fires after move legality confirmed, BEFORE any mutation. Can veto by returning `{ cancel: true, reason: "..." }`. The engine throws `MoveCancelledError` which the caller surfaces via toast.
**Scope-aware**: only fires for presets whose scope covers the mover.
Use cases: stamina systems, action-point economies, cooldowns.
```ts
onBeforeMove({ engine, pieceId }) {
const stamina = engine.session.get(pieceId, "Stamina") as number ?? 0;
if (stamina < 1) return { cancel: true, reason: "Piece too tired" };
engine.session.insert(pieceId, "Stamina", stamina - 1);
}
```
#### `onAfterMove(ctx: MoveHookContext)`
Fires AFTER all move mutations but BEFORE terminal-state check. Used by king-heals, poisoned-squares.
Fires for EVERY active preset regardless of scope — the preset decides based on `ctx.mover`. (This asymmetry is historical — changing it would break existing presets. See Design Notes.)
#### `onTurnStart(ctx: TurnStartContext)`
Fires AFTER turn counter flips and AFTER `onAfterMove`, BEFORE legal-move computation for the new side. Ideal for:
- Regenerating per-piece resources (+1 Stamina up to max).
- Decrementing cooldowns.
- Refreshing auras / blessings.
**Scope-aware**: only fires for presets whose scope covers the new side-to-move.
### Terminal state
#### `onCheckGameResult(ctx: GameResultHookContext): GameResult | undefined`
Override the engine's default checkmate/stalemate/draw logic. First preset to return a non-undefined value wins. Used by:
- `capture-to-win` — first capture ends the game.
- `last-piece-standing` — annihilation replaces checkmate.
- `piece-hp` — suppresses default terminal check when kings can survive attacks.
### Self-check filter
#### `shouldFilterSelfCheck(ctx: SelfCheckFilterContext): boolean | undefined`
Opt out of the engine's "you can't leave your king in check" move filter. Used by `piece-hp` — with HP active, a king in check just takes damage, it doesn't lose.
Return `false` to skip the filter, `true` / `undefined` to keep it.
### Description
#### `describeMoveEffect(ctx: DescribeMoveEffectContext): string | undefined`
Contribute to the `MoveRecord.presetEffects` array. Move-list UI, PGN export, and replay systems read these for human-readable annotations.
```ts
describeMoveEffect({ mover, movingType, capturedType }) {
if (movingType === "queen" && capturedType !== null) {
return `${mover} queen fissioned into R+B`;
}
return undefined;
}
```
---
## Engine APIs available from hooks
Every hook receives `ctx.engine: ChessEngine`. Useful methods:
### `engine.session`
The rete Session — direct insert/retract/get. Read preset-declared facts here.
### `engine.spawnPiece(type, color, square, opts?): EntityId`
Create a piece. Fires `onPieceSpawn` on every active preset. Use this instead of direct session inserts when creating pieces mid-game (fission, summon, resurrection).
### `engine.dealDamage(target, amount, { kind, attacker? })`
Canonical damage primitive. Routes through the `onDamage` pipeline (scope-aware). Returns `{ died: boolean }`. Use this instead of direct retraction — HP-like absorber presets get a chance to intercept.
### `engine.emitEffect({ kind, square, ttl, data? })`
Push a visual effect to subscribers. UI renders it. Presets emit from inside their hooks; no subscribers = no-op.
### `engine.presetState<T>(id)`
Typed per-preset state bag. `{ get, set, delete, has, all }`. Backed by session facts, so serialization is free. Auto-cleared on deactivate.
### `engine.moveLog`
Read-only chronological list of `MoveRecord`s. Use from UI components or tests; presets typically don't need it.
### `engine.effectivePieceAttrs`
Full list of attribute keys currently treated as "piece state" — core + preset-declared. Use when you need to retract every attribute on an entity (e.g. custom death handling).
### `engine.setActivePresets(requests)`
Replace the active set. Fires `onDeactivate` for dropped ids and `onActivate` for new ids. Validates `incompatibleWith` + `requires` constraints.
---
## PieceTypeRegistry
Register new piece types.
```ts
import { PIECE_TYPE_REGISTRY } from "./piece-type-registry.js";
PIECE_TYPE_REGISTRY.register({
id: "cannon",
displayName: "Cannon",
moveGenerator: (session, id) => [/* LegalMove[] */],
attackProbe: (session, id, target) => /* boolean */,
assets: { white: cannonWhiteSvg, black: cannonBlackSvg },
});
```
The engine + check detection + UI all dispatch through the registry. Once registered, your custom type:
- Can be spawned via `engine.spawnPiece("cannon", ...)`.
- Participates in `engine.getAllLegalMoves()`.
- Contributes to `isSquareAttacked` / `isInCheck` / `isCheckmate`.
- Renders via UI `<Piece>` using the declared `assets`.
Register from a module-level side-effect import. Core FIDE types register from `presets/core-piece-types.ts`.
---
## Walkthrough: Building a Shield preset
```ts
// 1. Declare the attribute in ChessAttrMap (schema.ts):
declare module "../schema" {
interface ChessAttrMap {
Shield: number;
}
}
// 2. Register the preset:
PRESET_REGISTRY.register({
id: "piece-shield",
name: "Shield",
description: "Every piece has Shield=1. Absorbs one hit before HP.",
incompatibleWith: [],
requires: [],
pieceAttributes: ["Shield"],
onActivate({ engine }) {
for (const f of engine.session.allFacts()) {
if (f.attr !== "PieceType") continue;
if ((f.id as number) <= 0) continue;
if (!engine.session.contains(f.id, "Shield")) {
engine.session.insert(f.id, "Shield", 1);
}
}
},
onPieceSpawn({ engine, pieceId }) {
if (!engine.session.contains(pieceId, "Shield")) {
engine.session.insert(pieceId, "Shield", 1);
}
},
onDamage({ engine, target, amount }) {
if (!engine.session.contains(target, "Shield")) return undefined;
const current = engine.session.get(target, "Shield") as number;
if (current <= 0) return undefined;
engine.session.insert(target, "Shield", current - 1);
if (amount - 1 <= 0) return { consume: true, died: false };
return undefined; // let piece-hp / default handle the remainder
},
});
```
That's a full Shield preset in ~30 lines, zero edits to engine code. Activate it BEFORE piece-hp in the active set so it intercepts damage first.
---
## Design notes and gotchas
### Hook firing order
Within a single `applyMove`, hooks fire in this order:
1. `onBeforeMove` — scope-aware, can cancel.
2. `onBeforeCapture` — fires if the move is a capture. First consumer owns the capture mechanic.
3. `onDamage` — if no `onBeforeCapture` consumed, the engine routes target through this. Scope-aware by target color.
4. Move mutations (position update, promotion, en-passant, castling).
5. Duration tick (`turnsRemaining -= 1`), `onDeactivate` for expired presets.
6. `onAfterMove` — unscoped, all active presets.
7. `onTurnStart` — scope-aware by new side-to-move.
8. `onCheckGameResult` — all presets, first non-undefined wins.
9. `describeMoveEffect` — all presets contribute `presetEffects` to the MoveRecord.
### Registration order determines dispatch order
For hooks that iterate presets (`onDamage`, `onCheckGameResult`), the first preset to consume wins. Order follows the active-set list, which follows the order in which presets were activated via `setActivePresets`. Registration order in `presets/index.ts` sets the DEFAULT activation order when all presets are enabled at once, but user-toggle order during a game is what actually matters.
If your preset needs to run before / after another, document the expectation. There's no priority system.
### Scope-aware vs unscoped
| Hook | Scope-aware? | Why |
|---|---|---|
| `onDamage` | Yes (target color) | A `scope=white` Shield only protects white pieces. |
| `onBeforeMove` | Yes (mover) | A `scope=white` veto doesn't block black's moves. |
| `onTurnStart` | Yes (new side to move) | Regen hooks should only fire for the color they care about. |
| `onBeforeCapture` | Yes (mover) | Inherited from pre-refactor semantics. |
| `onAfterMove` | No | Presets read `ctx.mover` and decide themselves. Breaking-change to flip. |
| `onCheckGameResult` | No | Terminal state is global. |
### Context objects are growable
All hook contexts are interface-defined and additive. Adding a field in a later release won't break existing hook implementations — they'll simply ignore the new field.
### Don't use `GAME_ENTITY` for preset state
The reserved `PRESET_STATE_ENTITY` + `engine.presetState<T>(id)` API is namespaced, serializes automatically, and clears on deactivate. Putting preset-specific data on `GAME_ENTITY` (like the old `capture-to-win.Winner` fact) works today but collides with future presets and doesn't auto-clear.
---
## Testing
`packages/chess/src/presets/test-utils.ts` exports:
- `pieceAt(engine, square)` — find piece on algebraic square.
- `hpOf(engine, id)` / `typeOf(engine, id)` / `exists(engine, id)` — attribute queries.
- `clearBoard(engine, { preserveKings })` — strip the board to minimal pieces.
- `placePiece(engine, type, color, square, opts?)` — direct session insert (bypasses spawnPiece).
For preset tests that exercise hooks, see:
- `damage-pipeline.test.ts` — damage + composition
- `preset-state.test.ts` — per-preset state bag
- `move-log.test.ts` — MoveRecord / describeMoveEffect
- `visual-effect.test.ts` — emitEffect / subscribeEffects
- `phase-hooks.test.ts` — onBeforeMove / onTurnStart
- `integration.test.ts` — Shield / Cannon / Berserker / Stamina end-to-end
---
## Post-landing backlog
Documented but NOT yet available:
- `onPieceRetract` — symmetric counterpart to `onPieceSpawn`. Needed for "death rattle" mechanics.
- Per-preset UI panels (not just overlays) — extension slot for sidebar widgets.
- Server-side piece-type manifest echo — when custom types are authored outside the shared `packages/chess`.
- Save-state migration — versioning for saves that predate attribute additions.
File issues or propose extensions via pull request.

View file

@ -6,16 +6,13 @@
*/
import { Session } from "@paratype/rete";
import type { EntityId } from "@paratype/rete";
import { GAME_ENTITY, type PieceType, type PieceColor } from "./schema.js";
import { generateStartingPosition } from "./starting-position.js";
import { getLegalPawnMoves } from "./rules/pawn.js";
import { getLegalKnightMoves } from "./rules/knight.js";
import {
getLegalRookMoves,
getLegalBishopMoves,
getLegalQueenMoves,
} from "./rules/sliding.js";
import { getLegalKingMoves } from "./rules/king.js";
GAME_ENTITY,
PRESET_STATE_ENTITY,
type PieceType,
type PieceColor,
} from "./schema.js";
import { generateStartingPosition } from "./starting-position.js";
import {
getCastlingMoves,
applyCastlingMove,
@ -33,6 +30,7 @@ import {
} from "./rules/promotion.js";
import {
filterSelfCheckMoves,
isInCheck,
isSquareAttacked,
} from "./rules/check.js";
import { isCheckmate } from "./rules/checkmate.js";
@ -44,28 +42,50 @@ import {
recordPosition,
isThreefoldRepetition,
} from "./rules/draws.js";
import { PIECE_ATTRS } from "./rules/capture.js";
import type { DamageContext } from "./presets/registry.js";
import { CORE_PIECE_ATTRS } from "./rules/capture.js";
import type {
BeforeMoveContext,
CaptureHookContext,
DamageContext,
DamageHookContext,
DescribeMoveEffectContext,
GameResultHookContext,
LifecycleContext,
MoveHookContext,
PieceSpawnContext,
PieceSpawnReason,
SelfCheckFilterContext,
TurnStartContext,
} from "./presets/registry.js";
import type { ChessAttrKey } from "./schema.js";
import type { LegalMove } from "./rules/types.js";
import {
ActivePresetSet,
type ActivationRequest,
} from "./presets/active-set.js";
import { PRESET_REGISTRY } from "./presets/registry.js";
import { PIECE_TYPE_REGISTRY } from "./presets/piece-type-registry.js";
// Importing from the barrel guarantees every preset module's
// side-effect registration has run before the first engine is created.
import "./presets/index.js";
type MoveGetter = (session: Session, pieceId: EntityId) => LegalMove[];
const PIECE_MOVE_GETTERS: Record<PieceType, MoveGetter> = {
pawn: getLegalPawnMoves,
knight: getLegalKnightMoves,
bishop: getLegalBishopMoves,
rook: getLegalRookMoves,
queen: getLegalQueenMoves,
king: getLegalKingMoves,
};
/**
* Look up the move generator for a piece type via the registry.
* Returns `null` for unknown types (degenerate — indicates a fact
* with a piece type nobody registered; the engine treats such pieces
* as immobile).
*
* This replaces the hardcoded `PIECE_MOVE_GETTERS` table that only
* knew about FIDE pieces. Custom types (Cannon, Amazon, Nightrider)
* register their move generators in the same registry and are
* dispatched automatically.
*/
function lookupMoveGenerator(type: string): MoveGetter | null {
const def = PIECE_TYPE_REGISTRY.get(type);
return def?.moveGenerator ?? null;
}
export type GameResult =
| "checkmate"
@ -81,6 +101,187 @@ export type GameResult =
| "black-wins"
| "ongoing";
/**
* Reserved attribute prefix for preset-state facts. Every preset-
* state attribute stored on PRESET_STATE_ENTITY is prefixed with
* this to guarantee no collision with game-level or piece-level
* attribute keys.
*
* Changing this value breaks serialized save-games that contain
* preset-state facts — don't.
*/
const PRESET_STATE_ATTR_PREFIX = "__preset__/";
/**
* Thrown from `applyMove` when a preset's `onBeforeMove` hook vetoes
* the move. The caller (UI / server) should catch this, surface
* `reason` to the user, and leave the game state unchanged — no
* mutation happens before the cancel check runs.
*
* Fatal the move attempt, not the session. Callers should NOT treat
* this as a server error.
*/
export class MoveCancelledError extends Error {
readonly presetId: string;
constructor(message: string, presetId: string) {
super(message);
this.name = "MoveCancelledError";
this.presetId = presetId;
}
}
/**
* A single line in the engine's move history.
*
* Every successful `applyMove` appends one of these to the engine's
* `moveLog`. Callers that need history (UI move-list panel, PGN
* export, replay, analysis) read this rather than diffing session
* facts.
*
* `presetEffects` is populated by presets implementing
* `describeMoveEffect`: each return value contributes one entry
* (presetId + human-readable summary). Example: queen-splits would
* push `{ presetId: "queen-splits", summary: "Queen split into
* Rook/Bishop" }` on a fission move.
*
* Growable — future fields should be optional so existing consumers
* don't break. Favor primitive/string values so the record is
* trivially JSON-serializable for save/export.
*/
/**
* An ephemeral visual effect emitted by a preset for the UI layer
* to render.
*
* Effects are decoupled from gameplay — the engine's state is
* authoritative and independent of whether anyone subscribed. Emit
* liberally from presets; the UI decides whether / how to render a
* given kind. Unknown kinds are rendered as a generic pulse by the
* default VisualEffectLayer.
*
* `kind` is a free-form string so presets can introduce new effect
* types (explosion, heal, poison, lightning, shield-break, …) without
* editing engine/UI tables. The UI layer dispatches to per-kind
* components; an unregistered kind falls back to a generic overlay.
*
* `square` is where the effect visually anchors. `null` is allowed
* for full-board effects (e.g. a "shockwave" that sweeps the whole
* board). `ttl` is how long (in ms) the effect should persist before
* auto-expiring.
*
* `data` is a typed-free-form bag for kind-specific payloads
* (color, intensity, direction, count). Presets document what they
* emit; renderers read what they need.
*/
export interface VisualEffect {
readonly kind: string;
readonly square: number | null;
readonly ttl: number;
readonly data?: Record<string, unknown>;
}
/** Handler signature for effect subscribers. Return nothing. */
export type VisualEffectHandler = (effect: VisualEffect) => void;
/** Unsubscribe callback returned by `subscribeEffects`. */
export type Unsubscribe = () => void;
export interface MoveRecord {
readonly from: number;
readonly to: number;
readonly mover: PieceColor;
readonly movingType: PieceType;
/** Captured piece's id BEFORE the capture resolved (null if no capture). */
readonly capturedId: EntityId | null;
/** Captured piece's type BEFORE the capture resolved (null if no capture). */
readonly capturedType: PieceType | null;
/** Did the move put the opponent in check? */
readonly isCheck: boolean;
/** Did the move end the game (checkmate or preset-terminal)? */
readonly terminal: boolean;
readonly isEnPassant: boolean;
readonly isCastling: boolean;
readonly promotion: PieceType | null;
/** Engine timestamp in ms (Date.now()); for client-side animation timing. */
readonly timestamp: number;
/** Non-empty when presets contributed effect descriptions. */
readonly presetEffects: ReadonlyArray<{ presetId: string; summary: string }>;
}
/**
* Typed accessor for a preset's slice of engine-scoped state.
*
* Obtain one via `ChessEngine.presetState<T>(presetId)`. Calls are
* scoped: two presets calling `state.set("x", 1)` with different
* preset IDs each get their own `x`.
*/
export interface PresetState<T extends Record<string, unknown>> {
/** Read a state key. Returns undefined when unset. */
get<K extends keyof T>(key: K): T[K] | undefined;
/** Write a state key. Overwrites any previous value. */
set<K extends keyof T>(key: K, value: T[K]): void;
/** Delete a state key. Returns true if it was set, false otherwise. */
delete<K extends keyof T>(key: K): boolean;
/** Returns the full state snapshot as a plain object. */
all(): Partial<T>;
/** True if `key` has been set. */
has<K extends keyof T>(key: K): boolean;
}
class PresetStateImpl<T extends Record<string, unknown>>
implements PresetState<T>
{
readonly #session: Session;
readonly #prefix: string;
constructor(session: Session, presetId: string) {
this.#session = session;
this.#prefix = `${PRESET_STATE_ATTR_PREFIX}${presetId}/`;
}
#attrOf(key: string): string {
return `${this.#prefix}${key}`;
}
get<K extends keyof T>(key: K): T[K] | undefined {
const attr = this.#attrOf(key as string);
if (!this.#session.contains(PRESET_STATE_ENTITY, attr)) return undefined;
return this.#session.get(PRESET_STATE_ENTITY, attr) as T[K];
}
set<K extends keyof T>(key: K, value: T[K]): void {
// The rete session validates that `value` is a legal FactValue
// (string | number | boolean | null). Passing objects here will
// throw — a deliberate constraint to keep facts serialization-safe.
this.#session.insert(
PRESET_STATE_ENTITY,
this.#attrOf(key as string),
value as unknown as import("@paratype/rete").FactValue,
);
}
delete<K extends keyof T>(key: K): boolean {
const attr = this.#attrOf(key as string);
if (!this.#session.contains(PRESET_STATE_ENTITY, attr)) return false;
this.#session.retract(PRESET_STATE_ENTITY, attr);
return true;
}
has<K extends keyof T>(key: K): boolean {
return this.#session.contains(PRESET_STATE_ENTITY, this.#attrOf(key as string));
}
all(): Partial<T> {
const result: Record<string, unknown> = {};
for (const f of this.#session.allFacts()) {
if ((f.id as number) !== (PRESET_STATE_ENTITY as number)) continue;
if (!f.attr.startsWith(this.#prefix)) continue;
const key = f.attr.slice(this.#prefix.length);
result[key] = f.value;
}
return result as Partial<T>;
}
}
export class ChessEngine {
public readonly session: Session;
/**
@ -96,6 +297,69 @@ export class ChessEngine {
*/
public readonly activePresets: ActivePresetSet;
/**
* Chronological log of every successful applyMove. Callers consume
* this read-only for move-history UIs, PGN export, analysis. Writing
* to it is a private concern of applyMove.
*
* Unbounded — games are short-lived enough that we don't need a
* ring buffer. If that ever changes, add a `maxLogSize` option.
*/
readonly #moveLog: MoveRecord[] = [];
/** Read-only view of the move log. */
get moveLog(): ReadonlyArray<MoveRecord> {
return this.#moveLog;
}
/**
* Active visual-effect subscribers. Presets call `engine.emitEffect`
* to push effects; UI layers call `subscribeEffects` to listen.
*
* Using a Set (not an Array) so unsubscribe is O(1) and insertion
* order doesn't matter (effects are fire-and-forget — we iterate
* the full set on every emit).
*/
readonly #effectHandlers = new Set<VisualEffectHandler>();
/**
* Emit a visual effect to all subscribers. Fire-and-forget —
* handlers that throw are isolated (caught) so one bad subscriber
* doesn't break others.
*
* Safe to call from inside any preset hook. The engine does NOT
* persist effects; they're pure UI signals. If no subscribers are
* attached, the call is essentially a no-op.
*/
emitEffect(effect: VisualEffect): void {
for (const handler of this.#effectHandlers) {
try {
handler(effect);
} catch (err) {
// Effect handlers are UI-side and shouldn't tank gameplay.
// Log to console so dev-mode surfaces the problem without
// throwing.
console.error("VisualEffect handler threw:", err);
}
}
}
/**
* Register a subscriber for visual effects. Returns a function that
* removes the subscription. Typically called from React `useEffect`
* on component mount, and the return is returned as the cleanup.
*
* Handlers are called synchronously from `emitEffect`. For React
* subscribers, the handler should schedule a state update rather
* than render inline — use `useSyncExternalStore` or equivalent.
*/
subscribeEffects(handler: VisualEffectHandler): Unsubscribe {
this.#effectHandlers.add(handler);
return () => {
this.#effectHandlers.delete(handler);
};
}
constructor(activePresets?: ActivePresetSet) {
this.session = new Session({ autoFire: false });
generateStartingPosition(this.session);
@ -103,6 +367,80 @@ export class ChessEngine {
this.activePresets = activePresets ?? new ActivePresetSet();
}
/**
* The full set of piece attributes the engine should treat as
* "per-piece state" for this game, combining FIDE's core attrs
* with any preset-declared additions.
*
* Used by the damage pipeline's default-death path, piece retract
* helpers inside presets (queen-splits fissioning the queen,
* explosive-rook blast fallback), and any future save-state
* serialization. This is the CANONICAL answer to "what facts
* represent a piece."
*
* Computed on every read because the active preset set is mutable;
* the list is tiny (< 10 entries in practice), so we don't cache.
* If perf becomes a concern, invalidate a cache in
* `setActivePresets` / `ActivePresetSet.replaceAll`.
*/
get effectivePieceAttrs(): readonly ChessAttrKey[] {
const attrs = new Set<ChessAttrKey>(CORE_PIECE_ATTRS);
for (const entry of this.activePresets.list()) {
const def = PRESET_REGISTRY.get(entry.id);
if (!def?.pieceAttributes) continue;
for (const a of def.pieceAttributes) attrs.add(a);
}
return [...attrs];
}
/**
* Typed, per-preset, per-engine state bag.
*
* Returns an accessor scoped to `presetId` that reads/writes facts
* on the reserved `PRESET_STATE_ENTITY`. Attribute keys are
* namespaced as `__preset__/${presetId}/${key}` under the hood so
* two presets can never collide.
*
* Because state is backed by session facts it:
* - serializes automatically with the rest of save-state (no extra
* plumbing — `session.allFacts()` already includes it)
* - is engine-scoped, so two concurrent games (server-side) hold
* independent state under the same preset id — no module-level
* globals
* - is cleared when the preset deactivates (see
* `clearPresetState` called from `setActivePresets` /
* `tickAfterMove`)
*
* The type parameter is trusted for convenience — `set("x", 5)`
* doesn't verify that `x` is `number` in `T`. Use sparingly or wrap
* in a factory function per preset that enforces its own shape.
*/
presetState<T extends Record<string, unknown> = Record<string, unknown>>(
presetId: string,
): PresetState<T> {
return new PresetStateImpl<T>(this.session, presetId);
}
/**
* Retract every preset-state fact owned by `presetId`. Called from
* `setActivePresets` and `tickAfterMove` when a preset deactivates,
* so stale state doesn't leak across activation cycles.
*/
private clearPresetState(presetId: string): void {
const prefix = `${PRESET_STATE_ATTR_PREFIX}${presetId}/`;
const toRetract = this.session
.allFacts()
.filter(
(f) =>
(f.id as number) === (PRESET_STATE_ENTITY as number) &&
f.attr.startsWith(prefix),
)
.map((f) => f.attr);
for (const attr of toRetract) {
this.session.retract(PRESET_STATE_ENTITY, attr);
}
}
/**
* Replace the active preset set and fire lifecycle hooks on transitions.
*
@ -131,15 +469,19 @@ export class ChessEngine {
this.activePresets.replaceAll(requests);
const newIds = new Set(requests.map((r) => r.id));
const ctx: LifecycleContext = { engine: this };
for (const id of oldIds) {
if (newIds.has(id)) continue;
const def = PRESET_REGISTRY.get(id);
def?.onDeactivate?.(this);
def?.onDeactivate?.(ctx);
// Clear preset-state AFTER onDeactivate so the hook can read
// (or explicitly preserve) its own state during teardown.
this.clearPresetState(id);
}
for (const req of requests) {
if (oldIds.has(req.id)) continue;
const def = PRESET_REGISTRY.get(req.id);
def?.onActivate?.(this);
def?.onActivate?.(ctx);
}
}
@ -158,14 +500,69 @@ export class ChessEngine {
color: PieceColor,
): boolean {
let consumed = false;
const ctx: CaptureHookContext = {
engine: this,
attacker,
target,
mover: color,
};
for (const preset of this.activePresets.getForColor(color)) {
if (!preset.onBeforeCapture) continue;
const result = preset.onBeforeCapture(this, attacker, target);
const result = preset.onBeforeCapture(ctx);
if (result && result.consume === true) consumed = true;
}
return consumed;
}
/**
* Create a new piece entity on `square` and fire `onPieceSpawn` hooks.
*
* This is the CANONICAL spawn path. Every code site that materializes
* a piece — the queen-splits fission, promotion, hypothetical
* summon/resurrect presets — should go through here so:
* - `onPieceSpawn` hooks get a chance to seed preset-declared
* attributes (Hp from piece-hp, Shield from piece-shield, …)
* WITHOUT those presets having to implement idempotent
* onActivate scans.
* - core attrs are inserted in a consistent order.
* - new spawn reasons can be added to the `PieceSpawnReason` union
* without editing this function.
*
* The initial starting-position generation does NOT go through here
* (it precedes any active presets — nothing to hook). Preset-authored
* initial placements should activate AFTER piece seeding or use
* this function explicitly in their `onActivate`.
*/
spawnPiece(
type: PieceType,
color: PieceColor,
square: number,
opts: {
readonly reason?: PieceSpawnReason;
readonly hasMoved?: boolean;
} = {},
): EntityId {
const id = this.session.nextId();
this.session.insert(id, "PieceType", type);
this.session.insert(id, "Color", color);
this.session.insert(id, "Position", square);
this.session.insert(id, "HasMoved", opts.hasMoved ?? false);
const ctx: PieceSpawnContext = {
engine: this,
pieceId: id,
type,
color,
square,
reason: opts.reason ?? "summon",
};
for (const entry of this.activePresets.list()) {
const def = PRESET_REGISTRY.get(entry.id);
def?.onPieceSpawn?.(ctx);
}
return id;
}
/**
* Deal `amount` damage to `target`, running it through the preset
* damage pipeline before applying the default kill-on-damage rule.
@ -199,21 +596,44 @@ export class ChessEngine {
): { died: boolean } {
if (amount <= 0) return { died: false };
// Consult damage interceptors in active-preset list order. First
// consumer wins. Scope is not considered here because damage is a
// board-level event that can strike any piece regardless of whose
// turn it is (e.g. explosive rook hitting friendly pieces).
// Scope-aware dispatch: pre-resolve the target's color so we can
// skip presets whose scope doesn't cover it. A `scope=white` preset
// only damages/protects white pieces; without this filter, a white-
// only Shield preset would absorb damage on black pieces too.
// Presets without a color-sensitive hook opt in to universal
// dispatch by leaving scope as "both" (the default).
const targetColor = this.session.get(target, "Color") as
| PieceColor
| undefined;
const hookCtx: DamageHookContext = {
engine: this,
target,
amount,
kind: ctx.kind,
...(ctx.attacker !== undefined ? { attacker: ctx.attacker } : {}),
};
for (const entry of this.activePresets.list()) {
// If we know the target's color, require the preset's scope to
// cover that color. If we don't (degenerate — target has no
// Color fact), fire on every preset regardless.
if (
targetColor !== undefined &&
entry.scope !== "both" &&
entry.scope !== targetColor
) {
continue;
}
const def = PRESET_REGISTRY.get(entry.id);
const result = def?.onDamage?.(this, target, amount, ctx);
const result = def?.onDamage?.(hookCtx);
if (result?.consume === true) {
return { died: result.died === true };
}
}
// Default: any damage is lethal. Retract all piece attributes so
// downstream queries see the piece as truly gone.
for (const attr of PIECE_ATTRS) {
// Default: any damage is lethal. Retract every effective piece
// attribute (core + preset-declared) so downstream queries see the
// piece as truly gone.
for (const attr of this.effectivePieceAttrs) {
if (this.session.contains(target, attr)) {
this.session.retract(target, attr);
}
@ -240,7 +660,7 @@ export class ChessEngine {
.filter(p => p.type !== undefined);
for (const piece of pieces) {
const getter = PIECE_MOVE_GETTERS[piece.type];
const getter = lookupMoveGenerator(piece.type);
if (!getter) continue;
let pieceMoves = getter(this.session, piece.id);
@ -304,8 +724,9 @@ export class ChessEngine {
// This is how `piece-hp` allows the king to stay on an attacked
// square — a "hit" costs HP rather than losing the game.
let applyFilter = true;
const selfCheckCtx: SelfCheckFilterContext = { engine: this, color };
for (const preset of this.activePresets.getForColor(color)) {
if (preset.shouldFilterSelfCheck?.(this, color) === false) {
if (preset.shouldFilterSelfCheck?.(selfCheckCtx) === false) {
applyFilter = false;
break;
}
@ -315,6 +736,28 @@ export class ChessEngine {
applyMove(move: LegalMove, promoteTo: PieceType = "queen"): GameResult {
const color = this.getCurrentTurn();
// Phase hook: give presets a chance to veto the move. Scope-aware
// (fires only for presets whose scope covers the mover). We do
// this BEFORE any mutation so a veto leaves state clean.
const beforeCtx: BeforeMoveContext = {
engine: this,
mover: color,
pieceId: move.pieceId,
from: move.from,
to: move.to,
isCapture: move.isCapture === true,
};
for (const preset of this.activePresets.getForColor(color)) {
const result = preset.onBeforeMove?.(beforeCtx);
if (result?.cancel === true) {
throw new MoveCancelledError(
result.reason ?? `Move cancelled by preset "${preset.id}"`,
preset.id,
);
}
}
const facts = this.session.allFacts();
const movingType = facts.find(
f => f.id === move.pieceId && f.attr === "PieceType",
@ -329,6 +772,26 @@ export class ChessEngine {
const isCastling = (move as CastlingMove).isCastling === true;
// Capture pre-move state for the MoveRecord we'll log at the end.
// Taking the snapshot NOW — before any mutation — is the only way
// to know what was on the destination square, since the capture
// path may retract it mid-function.
const capturedIdForLog: EntityId | null = move.isCapture
? (isEnPassant
? this.getPieceAt(
color === "white"
? ((move.to - 8) as number)
: ((move.to + 8) as number),
)
: this.getPieceAt(move.to))
: null;
const capturedTypeForLog: PieceType | null =
capturedIdForLog !== null
? (facts.find(
(f) => f.id === capturedIdForLog && f.attr === "PieceType",
)?.value as PieceType | undefined) ?? null
: null;
if (isEnPassant) {
// En passant captures the pawn on the SKIPPED square, not on
// `move.to`. We still fire `onBeforeCapture` first so presets
@ -440,10 +903,12 @@ export class ChessEngine {
// ticks only when white plays; a `scope=both` ticks on every
// half-move. Entries reaching 0 are removed AND fire onDeactivate
// so they can tear down any board state they installed.
const lifecycleCtx: LifecycleContext = { engine: this };
const expired = this.activePresets.tickAfterMove(color);
for (const id of expired) {
const def = PRESET_REGISTRY.get(id);
def?.onDeactivate?.(this);
def?.onDeactivate?.(lifecycleCtx);
this.clearPresetState(id);
}
// Post-move preset hooks: fire against EVERY still-active preset
@ -451,12 +916,73 @@ export class ChessEngine {
// responsibility — king-heals affects the non-mover, poisoned-squares
// affects the mover, so a single engine-level scope filter can't
// serve both.
const moveCtx: MoveHookContext = { engine: this, mover: color };
for (const entry of this.activePresets.list()) {
const def = PRESET_REGISTRY.get(entry.id);
def?.onAfterMove?.(this, color);
def?.onAfterMove?.(moveCtx);
}
return this.checkGameResult();
// Phase hook: a new turn is starting (nextColor is now to move).
// Scope-aware — presets scoped to a specific color only fire when
// that color's turn is beginning. Ideal for resource regen /
// cooldown ticks — runs BEFORE the player asks for their legal
// moves, so regenerated stamina / refreshed cooldowns are
// reflected in the first legal-move query.
const turnStartCtx: TurnStartContext = { engine: this, turn: nextColor };
for (const preset of this.activePresets.getForColor(nextColor)) {
preset.onTurnStart?.(turnStartCtx);
}
// Determine terminal state BEFORE we log, so the MoveRecord
// reflects game-over status on the move that caused it.
const gameResult = this.checkGameResult();
const terminal = gameResult !== "ongoing";
// Check-detection: after the move + preset hooks, is the opponent
// (the side whose turn is NOW) in check?
const opponentInCheck = isInCheck(this.session, nextColor);
// Collect preset contributions to the move description.
const describeCtx: DescribeMoveEffectContext = {
engine: this,
mover: color,
from: move.from,
to: move.to,
movingType,
capturedType: capturedTypeForLog,
isEnPassant,
isCastling,
promotion:
movingType === "pawn" && isPromotionMove(effectiveTo, color)
? ((move as LegalMove & { promoteTo?: PieceType }).promoteTo ?? promoteTo)
: null,
};
const presetEffects: Array<{ presetId: string; summary: string }> = [];
for (const entry of this.activePresets.list()) {
const def = PRESET_REGISTRY.get(entry.id);
const summary = def?.describeMoveEffect?.(describeCtx);
if (summary !== undefined && summary !== "") {
presetEffects.push({ presetId: entry.id, summary });
}
}
this.#moveLog.push({
from: move.from,
to: move.to,
mover: color,
movingType,
capturedId: capturedIdForLog,
capturedType: capturedTypeForLog,
isCheck: opponentInCheck,
terminal,
isEnPassant,
isCastling,
promotion: describeCtx.promotion as PieceType | null,
timestamp: Date.now(),
presetEffects,
});
return gameResult;
}
checkGameResult(): GameResult {
@ -464,9 +990,10 @@ export class ChessEngine {
// in registration order. First non-undefined return wins. This lets
// capture-to-win and last-piece-standing redefine "game over"
// without touching engine internals.
const resultCtx: GameResultHookContext = { engine: this };
for (const entry of this.activePresets.list()) {
const def = PRESET_REGISTRY.get(entry.id);
const override = def?.onCheckGameResult?.(this);
const override = def?.onCheckGameResult?.(resultCtx);
if (override !== undefined) return override;
}

View file

@ -6,25 +6,32 @@
* capture ends the game first.
*
* Wiring:
* - `onBeforeCapture` — record the capturer's color on the game
* entity via a `Winner` fact. Does NOT consume the capture, so the
* engine's default retract-and-move still runs (the target piece
* dies normally, the attacker advances onto its square). This
* keeps the final board state intuitive for players to inspect
* ("why is white's pawn on d5?") rather than freezing the board
* mid-capture.
* - `onCheckGameResult` — if a Winner fact was recorded, convert
* it into the corresponding GameResult. Otherwise return undefined
* and let the default checkmate/stalemate logic run (nothing
* to do until the first capture happens).
* - `onBeforeCapture` — record the capturer's color in preset-
* scoped state via `engine.presetState("capture-to-win")`. Does
* NOT consume the capture, so the engine's default retract-and-
* move still runs (the target piece dies normally, the attacker
* advances onto its square). This keeps the final board state
* intuitive for players to inspect.
* - `onCheckGameResult` — if a winner was recorded, convert it
* into the corresponding GameResult. Otherwise return undefined
* and let the default checkmate/stalemate logic run.
*
* State migration note: the winner used to live as a `Winner` fact
* on `GAME_ENTITY`, alongside real game-level facts (Turn, etc).
* Post-refactor it lives in the preset's dedicated state bag so
* other presets can't collide, the state is auto-cleared on
* deactivate, and `Winner` stays off the shared game entity.
*
* Incompatible with `last-piece-standing` — both redefine "when is
* the game over" and would compete for the onCheckGameResult hook.
*/
import { PRESET_REGISTRY } from "./registry.js";
import { GAME_ENTITY, type PieceColor } from "../schema.js";
import type { ChessEngine, GameResult } from "../engine.js";
import type { EntityId } from "@paratype/rete";
import type { PieceColor } from "../schema.js";
import type { GameResult } from "../engine.js";
interface CaptureToWinState extends Record<string, unknown> {
winner: PieceColor;
}
PRESET_REGISTRY.register({
id: "capture-to-win",
@ -34,39 +41,29 @@ PRESET_REGISTRY.register({
incompatibleWith: ["last-piece-standing"],
requires: [],
onBeforeCapture(engine: ChessEngine, attacker: EntityId, _target: EntityId) {
const session = engine.session;
// Only record the first capture — don't stomp an earlier winner
// if multiple captures somehow occur in the same applyMove
// (shouldn't happen, but defensive).
if (session.contains(GAME_ENTITY, "Winner")) {
const existing = session.get(GAME_ENTITY, "Winner");
if (existing !== null) return; // already set, leave it
}
const colorFact = session
onBeforeCapture({ engine, attacker }) {
const state = engine.presetState<CaptureToWinState>("capture-to-win");
// Only record the FIRST capture — once set, never overwrite so
// multi-capture edge cases in the same applyMove don't drift.
if (state.has("winner")) return;
const colorFact = engine.session
.allFacts()
.find(f => f.id === attacker && f.attr === "Color");
.find((f) => f.id === attacker && f.attr === "Color");
if (!colorFact) return;
session.insert(GAME_ENTITY, "Winner", colorFact.value as PieceColor);
state.set("winner", colorFact.value as PieceColor);
// Don't consume — let the capture resolve normally so the board
// visibly reflects the killing blow.
},
onCheckGameResult(engine: ChessEngine): GameResult | undefined {
const session = engine.session;
if (!session.contains(GAME_ENTITY, "Winner")) return undefined;
const winner = session.get(GAME_ENTITY, "Winner");
onCheckGameResult({ engine }): GameResult | undefined {
const state = engine.presetState<CaptureToWinState>("capture-to-win");
const winner = state.get("winner");
if (winner === "white") return "white-wins";
if (winner === "black") return "black-wins";
return undefined; // "draw" or null — let default logic run
return undefined;
},
onDeactivate(engine: ChessEngine) {
// Clear any stored winner when the preset is turned off so the
// game doesn't stay in a won state after the rule is lifted.
const session = engine.session;
if (session.contains(GAME_ENTITY, "Winner")) {
session.retract(GAME_ENTITY, "Winner");
}
},
// No explicit onDeactivate needed: the engine automatically clears
// preset-state for this id via clearPresetState when we go inactive.
});

View file

@ -0,0 +1,106 @@
/**
* Registration of the six FIDE piece types in the PieceTypeRegistry.
*
* This module is imported from the presets barrel so piece types are
* available before any engine constructs a move.
*
* Piece types are registered with:
* - `moveGenerator` — the pseudo-legal move function from `rules/`.
* - `attackProbe` — "does this piece attack `target`?" used for
* check detection. For most types this is a thin wrapper over
* the move generator; pawns need their own because they attack
* diagonally without an enemy on the target square.
* - `assets` — the bundled SVG URLs per color.
*
* Custom piece types (Cannon, Amazon, etc.) register themselves the
* same way — typically from a preset's side-effect import.
*/
import { PIECE_TYPE_REGISTRY } from "./piece-type-registry.js";
import { getLegalPawnMoves } from "../rules/pawn.js";
import { getLegalKnightMoves } from "../rules/knight.js";
import {
getLegalRookMoves,
getLegalBishopMoves,
getLegalQueenMoves,
} from "../rules/sliding.js";
import { getLegalKingMoves } from "../rules/king.js";
import { getPiecePosition } from "../rules/board-queries.js";
import { pawnCaptureSqares } from "../rules/primitives.js";
import { pieceAssets } from "../assets/pieces/index.js";
import type { PieceAttackProbe, PieceMoveGenerator } from "./piece-type-registry.js";
import type { PieceColor } from "../schema.js";
/**
* Derive a "does this piece attack `target`?" probe from its move
* generator. Works for any piece type whose attack geometry EQUALS
* its move geometry. Pawns are the sole exception (see below).
*/
function movesAttackProbe(getter: PieceMoveGenerator): PieceAttackProbe {
return (session, pieceId, target) => {
for (const m of getter(session, pieceId)) {
if (m.to === target) return true;
}
return false;
};
}
/** Pawns attack diagonally regardless of what (or nothing) is there. */
const pawnAttackProbe: PieceAttackProbe = (session, pieceId, target) => {
const from = getPiecePosition(session, pieceId);
if (from === null) return false;
const colorVal = session.get(pieceId, "Color");
if (colorVal === undefined) return false;
const color = colorVal as PieceColor;
for (const sq of pawnCaptureSqares(from, color)) {
if (sq === target) return true;
}
return false;
};
PIECE_TYPE_REGISTRY.register({
id: "pawn",
displayName: "Pawn",
moveGenerator: getLegalPawnMoves,
attackProbe: pawnAttackProbe,
assets: { white: pieceAssets.white.pawn, black: pieceAssets.black.pawn },
});
PIECE_TYPE_REGISTRY.register({
id: "knight",
displayName: "Knight",
moveGenerator: getLegalKnightMoves,
attackProbe: movesAttackProbe(getLegalKnightMoves),
assets: { white: pieceAssets.white.knight, black: pieceAssets.black.knight },
});
PIECE_TYPE_REGISTRY.register({
id: "bishop",
displayName: "Bishop",
moveGenerator: getLegalBishopMoves,
attackProbe: movesAttackProbe(getLegalBishopMoves),
assets: { white: pieceAssets.white.bishop, black: pieceAssets.black.bishop },
});
PIECE_TYPE_REGISTRY.register({
id: "rook",
displayName: "Rook",
moveGenerator: getLegalRookMoves,
attackProbe: movesAttackProbe(getLegalRookMoves),
assets: { white: pieceAssets.white.rook, black: pieceAssets.black.rook },
});
PIECE_TYPE_REGISTRY.register({
id: "queen",
displayName: "Queen",
moveGenerator: getLegalQueenMoves,
attackProbe: movesAttackProbe(getLegalQueenMoves),
assets: { white: pieceAssets.white.queen, black: pieceAssets.black.queen },
});
PIECE_TYPE_REGISTRY.register({
id: "king",
displayName: "King",
moveGenerator: getLegalKingMoves,
attackProbe: movesAttackProbe(getLegalKingMoves),
assets: { white: pieceAssets.white.king, black: pieceAssets.black.king },
});

View file

@ -355,6 +355,76 @@ describe("queen-splits + piece-hp: fission only on kills", () => {
// poisoned-squares: damage pipeline integration
// ─────────────────────────────────────────────────────────────────────
// ─────────────────────────────────────────────────────────────────────
// engine.spawnPiece + onPieceSpawn — preset-agnostic spawn pipeline
// ─────────────────────────────────────────────────────────────────────
describe("engine.spawnPiece + onPieceSpawn: HP auto-seeds on fission-spawned pieces", () => {
it("queen-splits spawns rook+bishop; piece-hp onPieceSpawn seeds Hp=2 on both", () => {
const engine = new ChessEngine();
// Clear to a minimal board: white queen on d1, weakened black
// pawn on d4 (Hp=1 after we activate piece-hp).
const facts = engine.session.allFacts();
const toClear: EntityId[] = [];
for (const f of facts) {
if (f.attr !== "PieceType") continue;
if ((f.id as number) <= 0) continue;
if (f.value === "king") continue;
toClear.push(f.id);
}
for (const id of toClear) {
for (const attr of ["PieceType", "Color", "Position", "HasMoved", "Hp"] as const) {
if (engine.session.contains(id, attr)) engine.session.retract(id, attr);
}
}
const queenId = engine.session.nextId();
engine.session.insert(queenId, "PieceType", "queen");
engine.session.insert(queenId, "Color", "white");
engine.session.insert(queenId, "Position", algebraicToSquare("d1"));
const pawnId = engine.session.nextId();
engine.session.insert(pawnId, "PieceType", "pawn");
engine.session.insert(pawnId, "Color", "black");
engine.session.insert(pawnId, "Position", algebraicToSquare("d4"));
engine.session.insert(pawnId, "HasMoved", true);
// Activate queen-splits FIRST, then piece-hp. This used to be a
// broken ordering — the spawn helper in queen-splits never went
// through HP's onActivate, so fissioned pieces had no Hp.
// Post-refactor, queen-splits uses engine.spawnPiece which fires
// onPieceSpawn on every active preset → piece-hp seeds Hp=2.
engine.setActivePresets([
{ id: "queen-splits", scope: "both", turnsRemaining: null },
]);
engine.setActivePresets([
{ id: "queen-splits", scope: "both", turnsRemaining: null },
{ id: "piece-hp", scope: "both", turnsRemaining: null },
]);
// Pre-weaken the target so queen kills on her capture (fission
// only fires on kill, not poke).
engine.session.insert(pawnId, "Hp", 1);
const capture = engine.findMove(
algebraicToSquare("d1"),
algebraicToSquare("d4"),
);
expect(capture).not.toBeNull();
engine.applyMove(capture!);
// Rook spawned on d4 (capture square) — find it, check Hp.
const d4Now = pieceAt(engine, "d4")!;
expect(engine.session.get(d4Now, "PieceType")).toBe("rook");
expect(hpOf(engine, d4Now)).toBe(2);
// Bishop spawned on first clockwise-from-N empty square around d4
// (d5 is empty on our minimal board).
const d5Now = pieceAt(engine, "d5");
expect(d5Now).not.toBeNull();
expect(engine.session.get(d5Now!, "PieceType")).toBe("bishop");
expect(hpOf(engine, d5Now!)).toBe(2);
});
});
describe("poisoned-squares routes through the damage pipeline", () => {
it("each tick deals 1 HP damage via the pipeline; piece dies when Hp hits 0", () => {
const engine = new ChessEngine();

View file

@ -22,7 +22,6 @@
* mechanic finite.
*/
import { PRESET_REGISTRY } from "./registry.js";
import type { ChessEngine } from "../engine.js";
import type { Session, EntityId } from "@paratype/rete";
import { fileOf, rankOf, squareOf } from "../coord.js";
import type { Square } from "../schema.js";
@ -47,7 +46,7 @@ PRESET_REGISTRY.register({
incompatibleWith: [],
requires: [],
onBeforeCapture(engine: ChessEngine, attacker: EntityId, target: EntityId) {
onBeforeCapture({ engine, attacker, target }) {
const session = engine.session;
const attackerTypeFact = session
.allFacts()
@ -97,6 +96,16 @@ PRESET_REGISTRY.register({
engine.dealDamage(v, 1, { kind: "explosion", attacker });
}
// Fire a visual effect anchored on the detonation square. The UI
// layer renders this as a brief blast overlay. Fire-and-forget —
// no subscribers = no-op, so tests and headless runs pay nothing.
engine.emitEffect({
kind: "explosion",
square: targetPos,
ttl: 600,
data: { radius: DETONATION_RADIUS, victimCount: victims.length },
});
// Advance the rook only if the target died — matches HP's general
// "non-lethal capture = attacker stays" semantics. Without HP,
// targetDied is always true so the rook always advances (standard

View file

@ -1,10 +1,18 @@
/**
* Preset rule barrel + registration side-effects (P3.4+).
*
* Importing this module guarantees all preset rules are registered in
* PRESET_REGISTRY. Consumers should import `./index.js` (never the registry
* directly) to ensure preset side-effect registration has run.
* Importing this module guarantees:
* - Core FIDE piece types are registered in PIECE_TYPE_REGISTRY.
* - All preset rules are registered in PRESET_REGISTRY.
*
* Consumers should import `./index.js` (never the registries
* directly) to ensure side-effect registration has run.
*/
// IMPORTANT: core-piece-types must register BEFORE any preset runs
// so preset onActivate hooks that inspect piece types see the full
// registry.
import "./core-piece-types.js";
import "./pawns-move-backward.js";
import "./double-pawn-sprint.js";
import "./pawn-diagonal-no-capture.js";

View file

@ -0,0 +1,426 @@
/**
* Integration tests proving that a third-party preset can use ONLY
* the public registry APIs to build real functionality. Each `describe`
* block defines a plausible preset inline, registers it, and then
* exercises it end-to-end through ChessEngine.
*
* If these tests fail, the extension API has a gap that should be
* fixed in the core before shipping.
*
* Scenarios covered:
* - Shield: a custom piece attribute absorbs damage before HP.
* - Cannon: a new piece type with Xiangqi-like capture geometry.
* - Berserker cooldown: per-preset state survives moves, clears on
* deactivate.
* - Pawn stamina: onBeforeMove veto + onTurnStart regen, both
* scope-aware.
*/
import { describe, it, expect } from "vitest";
import "./index.js";
import type { EntityId } from "@paratype/rete";
import { ChessEngine, MoveCancelledError } from "../engine.js";
import { algebraicToSquare } from "../coord.js";
import { PRESET_REGISTRY } from "./registry.js";
import { PIECE_TYPE_REGISTRY } from "./piece-type-registry.js";
import type { LegalMove } from "../rules/types.js";
import { clearBoard, pieceAt, placePiece, hpOf, exists } from "./test-utils.js";
import { CORE_PIECE_ATTRS } from "../rules/capture.js";
import { isInCheck } from "../rules/check.js";
// ─────────────────────────────────────────────────────────────────────
// 1. Shield attribute preset
//
// A piece with Shield absorbs 1 damage per turn before HP kicks in.
// Proves:
// - preset can declare a new piece attribute
// - onDamage can intercept BEFORE piece-hp and return consume:true
// - effectivePieceAttrs cleanup on death removes Shield facts
// ─────────────────────────────────────────────────────────────────────
// Extend the ChessAttrMap via module augmentation so the new attr is
// typed. In a real preset this would live in the preset's own file.
declare module "../schema" {
interface ChessAttrMap {
Shield: number;
}
}
const SHIELD_PRESET_ID = "test-piece-shield";
PRESET_REGISTRY.register({
id: SHIELD_PRESET_ID,
name: "Piece Shield",
description: "Every piece starts with Shield=1. Damage consumes shield before HP.",
incompatibleWith: [],
requires: [],
pieceAttributes: ["Shield"],
onActivate({ engine }) {
for (const f of engine.session.allFacts()) {
if (f.attr !== "PieceType") continue;
if ((f.id as number) <= 0) continue;
if (engine.session.contains(f.id, "Shield")) continue;
engine.session.insert(f.id, "Shield", 1);
}
},
onPieceSpawn({ engine, pieceId }) {
if (!engine.session.contains(pieceId, "Shield")) {
engine.session.insert(pieceId, "Shield", 1);
}
},
onDamage({ engine, target, amount }) {
// Opt out when there's no shield to absorb — let the next
// interceptor (e.g. piece-hp) or the default handle it.
if (!engine.session.contains(target, "Shield")) return undefined;
const current = engine.session.get(target, "Shield") as number;
if (current <= 0) return undefined;
// Absorb one point. `amount` above 1 passes the remainder through.
engine.session.insert(target, "Shield", current - 1);
const leftover = amount - 1;
if (leftover <= 0) {
return { consume: true, died: false };
}
// There's damage remaining — fall through to let piece-hp (or the
// default) handle it by NOT consuming.
return undefined;
},
});
describe("Custom attribute preset: piece-shield", () => {
it("absorbs 1 damage before HP", () => {
const engine = new ChessEngine();
// Shield activation FIRST — determines onDamage dispatch order.
// The shield preset claims damage events before piece-hp so HP
// stays untouched while Shield > 0.
engine.setActivePresets([
{ id: SHIELD_PRESET_ID, scope: "both", turnsRemaining: null },
{ id: "piece-hp", scope: "both", turnsRemaining: null },
]);
const pawn = pieceAt(engine, "e2")!;
expect(engine.session.get(pawn, "Shield")).toBe(1);
expect(hpOf(engine, pawn)).toBe(2);
engine.dealDamage(pawn, 1, { kind: "test" });
expect(engine.session.get(pawn, "Shield")).toBe(0);
expect(hpOf(engine, pawn)).toBe(2); // HP untouched
});
it("shield depletes then HP takes over", () => {
const engine = new ChessEngine();
engine.setActivePresets([
{ id: SHIELD_PRESET_ID, scope: "both", turnsRemaining: null },
{ id: "piece-hp", scope: "both", turnsRemaining: null },
]);
const pawn = pieceAt(engine, "e2")!;
engine.dealDamage(pawn, 1, { kind: "test" }); // Shield: 1→0
engine.dealDamage(pawn, 1, { kind: "test" }); // HP: 2→1
expect(hpOf(engine, pawn)).toBe(1);
expect(engine.session.get(pawn, "Shield")).toBe(0);
});
it("Shield fact is retracted on death via effectivePieceAttrs", () => {
const engine = new ChessEngine();
engine.setActivePresets([
{ id: SHIELD_PRESET_ID, scope: "both", turnsRemaining: null },
]);
const pawn = pieceAt(engine, "e2")!;
expect(engine.session.contains(pawn, "Shield")).toBe(true);
// Without HP, shield absorbs 1; next hit kills via default
// retract path which now includes "Shield" in the dynamic list.
engine.dealDamage(pawn, 1, { kind: "test" });
engine.dealDamage(pawn, 1, { kind: "test" });
expect(exists(engine, pawn)).toBe(false);
expect(engine.session.contains(pawn, "Shield")).toBe(false);
});
});
// ─────────────────────────────────────────────────────────────────────
// 2. Cannon — custom piece type (Xiangqi-inspired)
//
// Moves like a rook. Captures ONLY by jumping over exactly one
// intervening piece on the same rank/file. Proves:
// - custom piece types register + dispatch through engine.
// - check detection sees them as attackers.
// - UI asset lookup via registry works (visible via the registered
// `assets` object below, although we don't render it in this test).
// ─────────────────────────────────────────────────────────────────────
import type { Session } from "@paratype/rete";
/** Generate pseudo-legal cannon moves. */
function cannonMoveGen(session: Session, id: EntityId): LegalMove[] {
const facts = session.allFacts();
const pos = session.get(id, "Position");
if (typeof pos !== "number") return [];
const color = session.get(id, "Color");
if (color !== "white" && color !== "black") return [];
const from = pos;
const fromFile = from % 8;
const fromRank = Math.floor(from / 8);
const occupied = (sq: number): EntityId | null => {
const f = facts.find(
(fa) => fa.attr === "Position" && fa.value === sq,
);
return f ? (f.id as EntityId) : null;
};
const ownerOf = (eid: EntityId): string | undefined =>
facts.find((fa) => fa.id === eid && fa.attr === "Color")?.value as
| string
| undefined;
const moves: LegalMove[] = [];
const directions: ReadonlyArray<readonly [number, number]> = [
[1, 0], [-1, 0], [0, 1], [0, -1],
];
for (const [df, dr] of directions) {
let jumped = false;
for (let step = 1; step < 8; step++) {
const f = fromFile + df * step;
const r = fromRank + dr * step;
if (f < 0 || f > 7 || r < 0 || r > 7) break;
const sq = r * 8 + f;
const occupant = occupied(sq);
if (!jumped) {
if (occupant === null) {
// Empty — regular rook-like quiet move.
moves.push({ pieceId: id, from, to: sq, isCapture: false });
} else {
jumped = true; // next iteration checks for enemy-capture
}
} else {
// After jumping, ANY occupied square ends the ray — if it's
// enemy, that's a capture; otherwise nothing.
if (occupant !== null) {
if (ownerOf(occupant) !== color) {
moves.push({ pieceId: id, from, to: sq, isCapture: true });
}
break;
}
}
}
}
return moves;
}
// Use the pawn SVG as a stand-in asset for the test.
import { pieceAssets } from "../assets/pieces/index.js";
PIECE_TYPE_REGISTRY.register({
id: "cannon",
displayName: "Cannon",
moveGenerator: cannonMoveGen,
// For check detection we reuse the move generator — cannons "attack"
// exactly the squares they can move to capture.
attackProbe: (session, id, target) => {
for (const m of cannonMoveGen(session, id)) {
if (m.isCapture && m.to === target) return true;
}
return false;
},
assets: { white: pieceAssets.white.rook, black: pieceAssets.black.rook },
});
describe("Custom piece type: Cannon (Xiangqi-like)", () => {
it("moves like a rook when the path is clear; captures require a jump", () => {
const engine = new ChessEngine();
clearBoard(engine);
const cannon = placePiece(engine, "cannon", "white", "a1");
// Place a white pawn on a3 as a "jump platform" and a black pawn
// on a5 as the target.
placePiece(engine, "pawn", "white", "a3");
placePiece(engine, "pawn", "black", "a5");
const moves = cannonMoveGen(engine.session, cannon);
// Quiet moves up to a2 (a3 is blocked — can't move THROUGH
// without jumping).
expect(moves.some((m) => m.to === algebraicToSquare("a2") && !m.isCapture)).toBe(true);
// Capture on a5 via jump over a3.
expect(moves.some((m) => m.to === algebraicToSquare("a5") && m.isCapture)).toBe(true);
// CANNOT capture a3 directly (no jump — must leapfrog).
expect(moves.some((m) => m.to === algebraicToSquare("a3"))).toBe(false);
});
it("check detection sees cannon as an attacker", () => {
const engine = new ChessEngine();
clearBoard(engine);
// White cannon on a1. Black pawn on a4 as jump platform. Black king
// on a8.
placePiece(engine, "cannon", "white", "a1");
placePiece(engine, "pawn", "black", "a4");
const blackKingId = pieceAt(engine, "e8")!;
// Move black king to a8 for a direct line.
engine.session.insert(blackKingId, "Position", algebraicToSquare("a8"));
// isSquareAttacked should see the cannon attacking a8 via jump.
expect(isInCheck(engine.session, "black")).toBe(true);
});
});
// ─────────────────────────────────────────────────────────────────────
// 3. Berserker cooldown — uses presetState
// ─────────────────────────────────────────────────────────────────────
const BERSERKER_ID = "test-berserker-cooldown";
interface BerserkerState extends Record<string, unknown> {
lastRageTurn: number;
}
PRESET_REGISTRY.register({
id: BERSERKER_ID,
name: "Berserker Cooldown",
description: "Tracks a cooldown turn counter in presetState.",
incompatibleWith: [],
requires: [],
});
describe("Per-preset state bag (presetState)", () => {
it("state is written/read per-game and cleared on deactivation", () => {
const engine = new ChessEngine();
engine.setActivePresets([
{ id: BERSERKER_ID, scope: "both", turnsRemaining: null },
]);
const state = engine.presetState<BerserkerState>(BERSERKER_ID);
state.set("lastRageTurn", 4);
expect(state.get("lastRageTurn")).toBe(4);
// Different preset id — no collision.
const other = engine.presetState<BerserkerState>("piece-hp");
expect(other.get("lastRageTurn")).toBeUndefined();
// Deactivate → state cleared automatically.
engine.setActivePresets([]);
const afterDeact = engine.presetState<BerserkerState>(BERSERKER_ID);
expect(afterDeact.get("lastRageTurn")).toBeUndefined();
});
});
// ─────────────────────────────────────────────────────────────────────
// 4. Pawn stamina — phase hooks (onBeforeMove + onTurnStart)
// ─────────────────────────────────────────────────────────────────────
const STAMINA_ID = "test-pawn-stamina";
declare module "../schema" {
interface ChessAttrMap {
Stamina: number;
}
}
PRESET_REGISTRY.register({
id: STAMINA_ID,
name: "Pawn Stamina",
description: "Pawns need 1 Stamina to push; regenerates +1 per turn (max 2).",
incompatibleWith: [],
requires: [],
pieceAttributes: ["Stamina"],
onActivate({ engine }) {
for (const f of engine.session.allFacts()) {
if (f.attr !== "PieceType" || f.value !== "pawn") continue;
if ((f.id as number) <= 0) continue;
engine.session.insert(f.id, "Stamina", 2);
}
},
onPieceSpawn({ engine, pieceId, type }) {
if (type === "pawn") engine.session.insert(pieceId, "Stamina", 2);
},
onBeforeMove({ engine, pieceId }) {
const type = engine.session.get(pieceId, "PieceType");
if (type !== "pawn") return undefined;
const stamina = engine.session.contains(pieceId, "Stamina")
? (engine.session.get(pieceId, "Stamina") as number)
: 0;
if (stamina < 1) {
return { cancel: true, reason: "Pawn too tired to push (Stamina 0)" };
}
// Consume 1 stamina. Do it in onBeforeMove because onAfterMove
// can't veto, and the engine needs to know NOW whether the move
// is even allowed. (Consuming here = charged regardless of
// success; tests acknowledge this.)
engine.session.insert(pieceId, "Stamina", stamina - 1);
return undefined;
},
onTurnStart({ engine, turn }) {
// Regenerate each pawn of this color +1 stamina up to max 2.
const facts = engine.session.allFacts();
for (const f of facts) {
if (f.attr !== "PieceType" || f.value !== "pawn") continue;
const colorFact = facts.find(
(c) => c.id === f.id && c.attr === "Color",
);
if (colorFact?.value !== turn) continue;
const current = engine.session.contains(f.id, "Stamina")
? (engine.session.get(f.id, "Stamina") as number)
: 0;
if (current < 2) {
engine.session.insert(f.id, "Stamina", current + 1);
}
}
},
});
describe("Phase hooks (onBeforeMove + onTurnStart)", () => {
it("pawn with stamina 0 cannot move (onBeforeMove veto)", () => {
const engine = new ChessEngine();
engine.setActivePresets([
{ id: STAMINA_ID, scope: "both", turnsRemaining: null },
]);
const e2Pawn = pieceAt(engine, "e2")!;
// Drain stamina to 0.
engine.session.insert(e2Pawn, "Stamina", 0);
const move = engine.findMove(
algebraicToSquare("e2"),
algebraicToSquare("e4"),
)!;
expect(() => engine.applyMove(move)).toThrow(MoveCancelledError);
});
it("onTurnStart regenerates stamina on the appropriate color only", () => {
const engine = new ChessEngine();
engine.setActivePresets([
{ id: STAMINA_ID, scope: "both", turnsRemaining: null },
]);
// White e2 pawn starts with 2 stamina. Consume 1 via a push.
const e2Pawn = pieceAt(engine, "e2")!;
expect(engine.session.get(e2Pawn, "Stamina")).toBe(2);
engine.applyMove(
engine.findMove(algebraicToSquare("e2"), algebraicToSquare("e4"))!,
);
// After move: stamina 2 - 1 = 1 for white e2-pawn (now e4). BUT
// onTurnStart fired for BLACK next, not white — so white's
// stamina stays at 1.
const e4Pawn = pieceAt(engine, "e4")!;
expect(engine.session.get(e4Pawn, "Stamina")).toBe(1);
// Black's move — doesn't change white's stamina.
engine.applyMove(
engine.findMove(algebraicToSquare("a7"), algebraicToSquare("a6"))!,
);
// Now it's white's turn again. onTurnStart fired for white →
// e4 pawn's stamina regens from 1 back to 2.
expect(engine.session.get(e4Pawn, "Stamina")).toBe(2);
});
});
// ─────────────────────────────────────────────────────────────────────
// 5. Meta-assertion: no hardcoded PIECE_ATTRS literals outside core
// ─────────────────────────────────────────────────────────────────────
describe("Architecture invariants", () => {
it("CORE_PIECE_ATTRS excludes preset-owned attrs like Hp/Shield/Stamina", () => {
const core = CORE_PIECE_ATTRS as readonly string[];
expect(core).not.toContain("Hp");
expect(core).not.toContain("Shield");
expect(core).not.toContain("Stamina");
// Only the FIDE-minimum four are core.
expect(core.length).toBe(4);
});
it("engine.effectivePieceAttrs unions in preset-declared attrs", () => {
const engine = new ChessEngine();
engine.setActivePresets([
{ id: "piece-hp", scope: "both", turnsRemaining: null },
]);
expect(engine.effectivePieceAttrs).toContain("Hp");
engine.setActivePresets([]);
expect(engine.effectivePieceAttrs).not.toContain("Hp");
});
});

View file

@ -16,7 +16,7 @@
* Requires `piece-hp`; without it there's no Hp attribute to heal.
*/
import { PRESET_REGISTRY } from "./registry.js";
import type { ChessEngine } from "../engine.js";
import type { Session, EntityId } from "@paratype/rete";
import type { PieceColor } from "../schema.js";
import { isInCheck } from "../rules/check.js";
@ -42,13 +42,13 @@ PRESET_REGISTRY.register({
incompatibleWith: [],
requires: ["piece-hp"],
onAfterMove(engine: ChessEngine, moverColor) {
onAfterMove({ engine, mover }) {
// The NON-mover's king is the one potentially healing: it's the
// king belonging to the player whose turn just arrived. Heal only
// if that king isn't currently in check (being in check denies the
// heal — an intentional game-design lever that makes aggressive
// play strategically meaningful).
const color: PieceColor = moverColor === "white" ? "black" : "white";
const color: PieceColor = mover === "white" ? "black" : "white";
const kingId = findKing(engine.session, color);
if (kingId === null) return;
if (isInCheck(engine.session, color)) return;
@ -58,5 +58,17 @@ PRESET_REGISTRY.register({
const hp = session.get(kingId, "Hp") as number;
if (hp >= MAX_KING_HP) return;
session.insert(kingId, "Hp", hp + 1);
// Visual: a brief heal shimmer on the king's square. No subscriber
// = no-op (see engine.emitEffect).
const kingSquare = session.get(kingId, "Position");
if (typeof kingSquare === "number") {
engine.emitEffect({
kind: "heal",
square: kingSquare,
ttl: 400,
data: { hp: hp + 1 },
});
}
},
});

View file

@ -26,7 +26,7 @@
* game over".
*/
import { PRESET_REGISTRY } from "./registry.js";
import type { ChessEngine, GameResult } from "../engine.js";
import type { GameResult } from "../engine.js";
PRESET_REGISTRY.register({
id: "last-piece-standing",
@ -36,7 +36,7 @@ PRESET_REGISTRY.register({
incompatibleWith: ["capture-to-win"],
requires: [],
onCheckGameResult(engine: ChessEngine): GameResult | undefined {
onCheckGameResult({ engine }): GameResult | undefined {
// Count Position facts per color. We use Position rather than
// PieceType because a piece "exists on the board" iff it has a
// position; retracted pieces (captured) have no Position fact.

View file

@ -0,0 +1,105 @@
/**
* Tests for `ChessEngine.moveLog` + `describeMoveEffect` hook.
*/
import { describe, it, expect } from "vitest";
import "./index.js";
import { ChessEngine } from "../engine.js";
import { algebraicToSquare } from "../coord.js";
import { PRESET_REGISTRY } from "./registry.js";
describe("ChessEngine.moveLog", () => {
it("empty at start", () => {
const engine = new ChessEngine();
expect(engine.moveLog).toHaveLength(0);
});
it("one record appended per applyMove", () => {
const engine = new ChessEngine();
engine.applyMove(engine.findMove(algebraicToSquare("e2"), algebraicToSquare("e4"))!);
expect(engine.moveLog).toHaveLength(1);
const record = engine.moveLog[0]!;
expect(record.from).toBe(algebraicToSquare("e2"));
expect(record.to).toBe(algebraicToSquare("e4"));
expect(record.mover).toBe("white");
expect(record.movingType).toBe("pawn");
expect(record.capturedId).toBeNull();
expect(record.capturedType).toBeNull();
expect(record.isCheck).toBe(false);
expect(record.terminal).toBe(false);
expect(record.isEnPassant).toBe(false);
expect(record.isCastling).toBe(false);
expect(record.promotion).toBeNull();
expect(record.presetEffects).toEqual([]);
});
it("captures populate capturedId + capturedType from PRE-MOVE state", () => {
const engine = new ChessEngine();
engine.applyMove(engine.findMove(algebraicToSquare("e2"), algebraicToSquare("e4"))!);
engine.applyMove(engine.findMove(algebraicToSquare("d7"), algebraicToSquare("d5"))!);
const blackPawnOnD5 = engine.session
.allFacts()
.find((f) => f.attr === "Position" && f.value === algebraicToSquare("d5"));
engine.applyMove(engine.findMove(algebraicToSquare("e4"), algebraicToSquare("d5"))!);
const capture = engine.moveLog[2]!;
expect(capture.capturedId).toBe(blackPawnOnD5!.id);
expect(capture.capturedType).toBe("pawn");
});
it("isCheck flips true when a move delivers check", () => {
const engine = new ChessEngine();
// Fool's Mate: 1. f3 e5 2. g4 Qh4# → opponent (white) in check + mate.
engine.applyMove(engine.findMove(algebraicToSquare("f2"), algebraicToSquare("f3"))!);
engine.applyMove(engine.findMove(algebraicToSquare("e7"), algebraicToSquare("e5"))!);
engine.applyMove(engine.findMove(algebraicToSquare("g2"), algebraicToSquare("g4"))!);
engine.applyMove(engine.findMove(algebraicToSquare("d8"), algebraicToSquare("h4"))!);
const mate = engine.moveLog[3]!;
expect(mate.isCheck).toBe(true);
expect(mate.terminal).toBe(true);
});
});
describe("describeMoveEffect hook", () => {
// Register a throwaway preset that contributes a description for
// pawn moves, then unregister the side-effect by swapping it for
// the real one. Since PRESET_REGISTRY.register overwrites by id, we
// use a fresh id to avoid disturbing other tests.
const testPresetId = "test-describe-effect-pawn-reporter";
PRESET_REGISTRY.register({
id: testPresetId,
name: "Pawn Reporter",
description: "Test helper — describes pawn moves.",
incompatibleWith: [],
requires: [],
describeMoveEffect(ctx) {
if (ctx.movingType !== "pawn") return undefined;
return `${ctx.mover} pawn pushed`;
},
});
it("contributes an entry to presetEffects when returning a string", () => {
const engine = new ChessEngine();
engine.setActivePresets([
{ id: testPresetId, scope: "both", turnsRemaining: null },
]);
engine.applyMove(engine.findMove(algebraicToSquare("e2"), algebraicToSquare("e4"))!);
const record = engine.moveLog[0]!;
expect(record.presetEffects).toContainEqual({
presetId: testPresetId,
summary: "white pawn pushed",
});
});
it("omits an entry when returning undefined", () => {
const engine = new ChessEngine();
engine.setActivePresets([
{ id: testPresetId, scope: "both", turnsRemaining: null },
]);
// A knight move — the reporter returns undefined for non-pawns.
engine.applyMove(engine.findMove(algebraicToSquare("g1"), algebraicToSquare("f3"))!);
const record = engine.moveLog[0]!;
expect(record.presetEffects).toEqual([]);
});
});

View file

@ -0,0 +1,119 @@
/**
* Tests for the `onBeforeMove` + `onTurnStart` phase hooks.
*
* These hooks unblock resource-tracking presets (stamina, action
* points, cooldowns) that need to decide whether a move is legal
* AT PLAY TIME (not just geometrically) and to regenerate state on
* turn boundaries.
*/
import { describe, it, expect } from "vitest";
import "./index.js";
import { ChessEngine, MoveCancelledError } from "../engine.js";
import { algebraicToSquare } from "../coord.js";
import { PRESET_REGISTRY } from "./registry.js";
describe("onBeforeMove cancel", () => {
const blockerId = "test-onbeforemove-blocker";
PRESET_REGISTRY.register({
id: blockerId,
name: "Test Blocker",
description: "Rejects every e2→e4.",
incompatibleWith: [],
requires: [],
onBeforeMove(ctx) {
if (
ctx.from === algebraicToSquare("e2") &&
ctx.to === algebraicToSquare("e4")
) {
return { cancel: true, reason: "blocked for testing" };
}
return undefined;
},
});
it("throws MoveCancelledError when a preset cancels the move", () => {
const engine = new ChessEngine();
engine.setActivePresets([
{ id: blockerId, scope: "both", turnsRemaining: null },
]);
const move = engine.findMove(
algebraicToSquare("e2"),
algebraicToSquare("e4"),
)!;
expect(() => engine.applyMove(move)).toThrow(MoveCancelledError);
// State unchanged — pawn still on e2.
const e2Still = engine.session
.allFacts()
.find(
(f) => f.attr === "Position" && f.value === algebraicToSquare("e2"),
);
expect(e2Still).toBeDefined();
});
it("allows moves the preset doesn't cancel", () => {
const engine = new ChessEngine();
engine.setActivePresets([
{ id: blockerId, scope: "both", turnsRemaining: null },
]);
const move = engine.findMove(
algebraicToSquare("d2"),
algebraicToSquare("d4"),
)!;
expect(() => engine.applyMove(move)).not.toThrow();
});
it("scope-aware: a white-scoped preset doesn't veto black's moves", () => {
const engine = new ChessEngine();
engine.setActivePresets([
{ id: blockerId, scope: "white", turnsRemaining: null },
]);
// White's e2→e4 — same blocked rule, white scope applies.
const whiteMove = engine.findMove(
algebraicToSquare("e2"),
algebraicToSquare("e4"),
)!;
expect(() => engine.applyMove(whiteMove)).toThrow(MoveCancelledError);
});
});
describe("onTurnStart fires after turn flip, scope-aware", () => {
const regenId = "test-onturnstart-regen";
let firedFor: string[] = [];
PRESET_REGISTRY.register({
id: regenId,
name: "Test Regen",
description: "Appends 'turn:color' to firedFor on each turn start.",
incompatibleWith: [],
requires: [],
onTurnStart(ctx) {
firedFor.push(ctx.turn);
},
});
it("fires with nextColor after every successful move", () => {
const engine = new ChessEngine();
firedFor = [];
engine.setActivePresets([
{ id: regenId, scope: "both", turnsRemaining: null },
]);
engine.applyMove(engine.findMove(algebraicToSquare("e2"), algebraicToSquare("e4"))!);
expect(firedFor).toEqual(["black"]);
engine.applyMove(engine.findMove(algebraicToSquare("e7"), algebraicToSquare("e5"))!);
expect(firedFor).toEqual(["black", "white"]);
});
it("scope-aware: a white-scoped preset only fires when white's turn starts", () => {
const engine = new ChessEngine();
firedFor = [];
engine.setActivePresets([
{ id: regenId, scope: "white", turnsRemaining: null },
]);
// After white's move → black's turn starts → scope=white DOESN'T fire.
engine.applyMove(engine.findMove(algebraicToSquare("e2"), algebraicToSquare("e4"))!);
expect(firedFor).toEqual([]);
// After black's move → white's turn starts → scope=white DOES fire.
engine.applyMove(engine.findMove(algebraicToSquare("e7"), algebraicToSquare("e5"))!);
expect(firedFor).toEqual(["white"]);
});
});

View file

@ -51,7 +51,7 @@
* they all use the damage pipeline. No more hardcoded incompatibilities.
*/
import { PRESET_REGISTRY } from "./registry.js";
import type { ChessEngine, GameResult } from "../engine.js";
import type { GameResult } from "../engine.js";
import type { Session, EntityId } from "@paratype/rete";
/** Starting HP for every piece. Future work: make this per-type so
@ -72,10 +72,6 @@ function iteratePieceIds(session: Session): EntityId[] {
return [...ids];
}
/** Piece attributes cleared when HP hits 0 (piece dies). Kept in
* lockstep with the canonical list in rules/capture.ts. */
const PIECE_ATTRS = ["PieceType", "Color", "Position", "HasMoved", "Hp"] as const;
PRESET_REGISTRY.register({
id: "piece-hp",
name: "Hit Points",
@ -83,8 +79,16 @@ PRESET_REGISTRY.register({
"Every piece has 2 HP. Damage (capture, explosion, poison…) deals 1 HP instead of immediately killing. A piece only dies when its HP hits 0; until then the attacker doesn't advance — the hit becomes a 'poke'.",
incompatibleWith: [],
requires: [],
// We OWN the Hp attribute. The engine unions this into
// effectivePieceAttrs while we're active, so the default damage
// retract path cleans Hp facts up automatically when pieces die
// from causes other than our own onDamage path (belt-and-suspenders
// — today we always self-retract on lethal damage, but if a future
// preset ever calls engine.dealDamage with an Hp we didn't seed,
// it'd still get cleaned up).
pieceAttributes: ["Hp"],
onActivate(engine: ChessEngine) {
onActivate({ engine }) {
const session = engine.session;
for (const id of iteratePieceIds(session)) {
// Idempotent: skip entities that already have an Hp fact, so
@ -95,7 +99,21 @@ PRESET_REGISTRY.register({
}
},
onDeactivate(engine: ChessEngine) {
/**
* Seed Hp on newly spawned pieces. Runs for every spawn reason —
* promotion, fission, summon, resurrection. The idempotence guard
* from `onActivate` is preserved here so callers that set Hp
* before calling spawnPiece (e.g. "spawn at half HP") can opt out
* by pre-inserting Hp before this hook fires. (Today nothing
* does that, but the guarantee lets future tuning opt in.)
*/
onPieceSpawn(ctx) {
const { engine, pieceId } = ctx;
if (engine.session.contains(pieceId, "Hp")) return;
engine.session.insert(pieceId, "Hp", DEFAULT_HP);
},
onDeactivate({ engine }) {
const session = engine.session;
for (const id of iteratePieceIds(session)) {
if (session.contains(id, "Hp")) {
@ -114,7 +132,7 @@ PRESET_REGISTRY.register({
* piece-hp composable with damage sources that vary in strength
* without needing per-source special cases.
*/
onDamage(engine: ChessEngine, target: EntityId, amount: number, _ctx) {
onDamage({ engine, target, amount }) {
// The engine short-circuits amount<=0 before we ever get here,
// but be defensive: if somehow invoked with 0, treat it as a
// no-op survival.
@ -131,10 +149,11 @@ PRESET_REGISTRY.register({
return { consume: true, died: false };
}
// Lethal. Retract all piece attrs ourselves so the engine doesn't
// need a second retract pass. Returning died:true tells upstream
// callers (capture path) that the attacker should advance.
for (const attr of PIECE_ATTRS) {
// Lethal. Retract all effective piece attrs ourselves (core +
// whatever other presets declared) so nothing is left behind.
// Returning died:true tells upstream callers (capture path) that
// the attacker should advance.
for (const attr of engine.effectivePieceAttrs) {
if (session.contains(target, attr)) session.retract(target, attr);
}
return { consume: true, died: true };
@ -167,7 +186,7 @@ PRESET_REGISTRY.register({
* run the default logic". Once a king is gone we return the winner
* directly.
*/
onCheckGameResult(engine: ChessEngine): GameResult | undefined {
onCheckGameResult({ engine }): GameResult | undefined {
const session = engine.session;
const colors = kingsPresent(session);
if (!colors.white && colors.black) return "black-wins";

View file

@ -0,0 +1,102 @@
/**
* Runtime registry of piece types.
*
* Piece types are no longer a closed TypeScript union — new types
* (Cannon, Amazon, Nightrider, fantasy variants) register here and
* participate in move generation, attack detection, UI rendering, and
* save-state serialization without any core engine edit.
*
* ## Registration
*
* Core FIDE types (pawn, knight, bishop, rook, queen, king) register
* themselves from `./core-piece-types.ts`, which is imported once at
* the top of the presets barrel. Custom types register via a preset's
* side-effect import, same pattern as preset rule registration.
*
* ## Access
*
* Engine dispatch tables (`PIECE_MOVE_GETTERS`, `ATTACK_PROBES`,
* `MOVE_GETTERS` in rules/checkmate.ts + rules/stalemate.ts) query
* the registry rather than holding their own hardcoded maps. UI
* `<Piece>` looks up SVG assets here too.
*
* ## Why strings instead of a branded type
*
* Piece-type ids are plain strings so third-party preset packages
* don't need to collaborate on a shared union. The registry's runtime
* check is the source of truth — unknown ids throw. Exhaustiveness
* checks on FIDE-only logic still work by narrowing to the built-in
* string-literal union where needed.
*/
import type { Session, EntityId } from "@paratype/rete";
import type { LegalMove } from "../rules/types.js";
/**
* A piece type's move generator: given the current WM + a piece id
* of this type, return every pseudo-legal move. "Pseudo-legal" means
* geometry + blockers are honored; self-check filtering happens
* later in the engine.
*/
export type PieceMoveGenerator = (
session: Session,
pieceId: EntityId,
) => LegalMove[];
/**
* A piece type's attack probe: "does this piece attack `target`?"
* Used for check detection. Different from the move generator
* because pawns attack diagonally without needing an enemy there —
* a king still can't step onto that square.
*/
export type PieceAttackProbe = (
session: Session,
pieceId: EntityId,
target: number,
) => boolean;
/**
* SVG asset URLs per color. The UI's `<Piece>` component reads these
* to render the piece. Bundled via Vite `?url` imports so each SVG
* becomes a URL string at build time.
*/
export interface PieceTypeAssets {
readonly white: string;
readonly black: string;
}
/**
* Full definition of a registered piece type.
*/
export interface PieceTypeDef {
readonly id: string;
readonly displayName: string;
readonly moveGenerator: PieceMoveGenerator;
readonly attackProbe: PieceAttackProbe;
readonly assets: PieceTypeAssets;
}
class PieceTypeRegistryClass {
readonly #byId = new Map<string, PieceTypeDef>();
register(def: PieceTypeDef): void {
this.#byId.set(def.id, def);
}
get(id: string): PieceTypeDef | undefined {
return this.#byId.get(id);
}
has(id: string): boolean {
return this.#byId.has(id);
}
getAll(): PieceTypeDef[] {
return [...this.#byId.values()];
}
ids(): string[] {
return [...this.#byId.keys()];
}
}
export const PIECE_TYPE_REGISTRY = new PieceTypeRegistryClass();

View file

@ -18,7 +18,6 @@
* activated via setActivePresets.
*/
import { PRESET_REGISTRY } from "./registry.js";
import type { ChessEngine } from "../engine.js";
import type { EntityId } from "@paratype/rete";
/** Poisoned central squares: d4=27, e4=28, d5=35, e5=36. Exported for
@ -33,7 +32,7 @@ PRESET_REGISTRY.register({
incompatibleWith: [],
requires: ["piece-hp"],
onAfterMove(engine: ChessEngine) {
onAfterMove({ engine }) {
const session = engine.session;
const facts = session.allFacts();
@ -52,8 +51,24 @@ PRESET_REGISTRY.register({
// 1 HP; when Hp hits 0 the piece is retracted. We tag the kind
// as "poison" so a future "poison-resistant" preset could short-
// circuit this without changing poisoned-squares' own code.
//
// Snapshot positions BEFORE the damage loop — if a piece dies, its
// Position fact is retracted and we lose the square for the effect.
const poisonedSquaresByVictim = new Map<EntityId, number>();
for (const id of victims) {
const pos = engine.session.get(id, "Position");
if (typeof pos === "number") poisonedSquaresByVictim.set(id, pos);
}
for (const id of victims) {
engine.dealDamage(id, 1, { kind: "poison" });
const sq = poisonedSquaresByVictim.get(id);
if (sq !== undefined) {
engine.emitEffect({
kind: "poison",
square: sq,
ttl: 250,
});
}
}
},
});

View file

@ -0,0 +1,171 @@
/**
* Tests for `ChessEngine.presetState` — the per-preset, per-engine
* state bag.
*
* Coverage:
* - basic read / write / delete / has / all
* - isolation across preset ids (no collision)
* - isolation across engines (no shared mutable state)
* - auto-clear on deactivate (including timer expiry)
* - explicit preservation by onDeactivate is NOT possible —
* clear runs AFTER the hook (design choice)
*/
import { describe, it, expect } from "vitest";
import "./index.js";
import { ChessEngine } from "../engine.js";
interface DemoState extends Record<string, unknown> {
counter: number;
name: string;
flag: boolean;
}
describe("ChessEngine.presetState — basic operations", () => {
it("set / get round-trips primitives", () => {
const engine = new ChessEngine();
const state = engine.presetState<DemoState>("demo");
state.set("counter", 5);
state.set("name", "hello");
state.set("flag", true);
expect(state.get("counter")).toBe(5);
expect(state.get("name")).toBe("hello");
expect(state.get("flag")).toBe(true);
});
it("unset keys return undefined", () => {
const engine = new ChessEngine();
const state = engine.presetState<DemoState>("demo");
expect(state.get("counter")).toBeUndefined();
});
it("has() reports presence correctly", () => {
const engine = new ChessEngine();
const state = engine.presetState<DemoState>("demo");
expect(state.has("counter")).toBe(false);
state.set("counter", 1);
expect(state.has("counter")).toBe(true);
});
it("delete removes a key and returns true; returns false for missing", () => {
const engine = new ChessEngine();
const state = engine.presetState<DemoState>("demo");
expect(state.delete("counter")).toBe(false);
state.set("counter", 42);
expect(state.delete("counter")).toBe(true);
expect(state.get("counter")).toBeUndefined();
});
it("set overwrites prior value", () => {
const engine = new ChessEngine();
const state = engine.presetState<DemoState>("demo");
state.set("counter", 1);
state.set("counter", 2);
expect(state.get("counter")).toBe(2);
});
it("all() returns the full snapshot", () => {
const engine = new ChessEngine();
const state = engine.presetState<DemoState>("demo");
state.set("counter", 3);
state.set("name", "x");
expect(state.all()).toEqual({ counter: 3, name: "x" });
});
});
describe("ChessEngine.presetState — isolation", () => {
it("two preset ids on the same engine don't collide", () => {
const engine = new ChessEngine();
const a = engine.presetState<DemoState>("preset-a");
const b = engine.presetState<DemoState>("preset-b");
a.set("counter", 1);
b.set("counter", 999);
expect(a.get("counter")).toBe(1);
expect(b.get("counter")).toBe(999);
});
it("two engines hold independent state under the same preset id", () => {
const e1 = new ChessEngine();
const e2 = new ChessEngine();
const s1 = e1.presetState<DemoState>("demo");
const s2 = e2.presetState<DemoState>("demo");
s1.set("counter", 100);
s2.set("counter", 200);
expect(s1.get("counter")).toBe(100);
expect(s2.get("counter")).toBe(200);
});
});
describe("ChessEngine.presetState — auto-clear on deactivate", () => {
it("state is cleared when preset is deactivated via setActivePresets", () => {
const engine = new ChessEngine();
// piece-hp has real activate/deactivate; abuse its id for state.
engine.setActivePresets([
{ id: "piece-hp", scope: "both", turnsRemaining: null },
]);
const state = engine.presetState<DemoState>("piece-hp");
state.set("counter", 7);
expect(state.get("counter")).toBe(7);
// Deactivate by replacing with an empty set.
engine.setActivePresets([]);
// New accessor reads the post-clear state.
const fresh = engine.presetState<DemoState>("piece-hp");
expect(fresh.get("counter")).toBeUndefined();
});
it("state survives scope / duration changes on the same id", () => {
const engine = new ChessEngine();
engine.setActivePresets([
{ id: "piece-hp", scope: "both", turnsRemaining: null },
]);
const state = engine.presetState<DemoState>("piece-hp");
state.set("counter", 11);
// Same id, different turnsRemaining — should be a continuous
// activation, not deactivate-then-activate.
engine.setActivePresets([
{ id: "piece-hp", scope: "both", turnsRemaining: 10 },
]);
expect(state.get("counter")).toBe(11);
});
});
describe("capture-to-win migrated to presetState", () => {
it("first capture sets winner; onCheckGameResult reads it", () => {
const engine = new ChessEngine();
engine.setActivePresets([
{ id: "capture-to-win", scope: "both", turnsRemaining: null },
]);
// Before any capture: ongoing.
expect(engine.checkGameResult()).toBe("ongoing");
// Simulate a white capture: find any move, if e4 is available
// that's fine but we need an actual capture. Use a scripted game
// where white captures first. 1. e4 d5 2. exd5 → white wins.
const e4 = engine.findMove(12, 28)!; // e2->e4
engine.applyMove(e4);
const d5 = engine.findMove(51, 35)!; // d7->d5
engine.applyMove(d5);
const exd5 = engine.findMove(28, 35)!;
expect(exd5.isCapture).toBe(true);
const result = engine.applyMove(exd5);
expect(result).toBe("white-wins");
});
it("deactivation clears the winner state", () => {
const engine = new ChessEngine();
engine.setActivePresets([
{ id: "capture-to-win", scope: "both", turnsRemaining: null },
]);
// Force a winner.
engine.applyMove(engine.findMove(12, 28)!);
engine.applyMove(engine.findMove(51, 35)!);
engine.applyMove(engine.findMove(28, 35)!);
expect(engine.checkGameResult()).toBe("white-wins");
// Deactivate → winner state cleared → game result falls back to
// normal logic.
engine.setActivePresets([]);
expect(engine.checkGameResult()).toBe("ongoing");
});
});

View file

@ -57,17 +57,12 @@ const CLOCKWISE_NEIGHBOURS: ReadonlyArray<readonly [number, number]> = [
[-1, 1], // NW
];
const PIECE_ATTRS = [
"PieceType",
"Color",
"Position",
"HasMoved",
"Hp",
] as const;
function retractEntity(session: Session, id: EntityId): void {
for (const attr of PIECE_ATTRS) {
if (session.contains(id, attr)) session.retract(id, attr);
/** Retract every effective piece attr (core + preset-declared) for
* an entity. Called when the queen is removed as part of fission —
* we need to nuke her completely so no leftover facts linger. */
function retractEntity(engine: ChessEngine, id: EntityId): void {
for (const attr of engine.effectivePieceAttrs) {
if (engine.session.contains(id, attr)) engine.session.retract(id, attr);
}
}
@ -81,20 +76,10 @@ function pieceAtSquare(session: Session, sq: Square): EntityId | null {
return null;
}
/** Spawn a new piece entity. Returns the new id. */
function spawnPiece(
session: Session,
type: "rook" | "bishop",
color: PieceColor,
square: Square,
): EntityId {
const id = session.nextId();
session.insert(id, "PieceType", type);
session.insert(id, "Color", color);
session.insert(id, "Position", square);
session.insert(id, "HasMoved", true);
return id;
}
// spawnPiece helper lived here historically. It's now
// `engine.spawnPiece(...)` — goes through the standard onPieceSpawn
// pipeline so preset-declared attributes (Hp, Shield, …) get seeded
// on fission-spawned pieces automatically.
PRESET_REGISTRY.register({
id: "queen-splits",
@ -104,7 +89,7 @@ PRESET_REGISTRY.register({
incompatibleWith: [],
requires: [],
onBeforeCapture(engine: ChessEngine, attacker: EntityId, target: EntityId) {
onBeforeCapture({ engine, attacker, target }) {
const session = engine.session;
const attackerTypeFact = session
.allFacts()
@ -138,8 +123,18 @@ PRESET_REGISTRY.register({
// Target died (standard path). Retract the queen (she fissions)
// and spawn a rook on the capture square + a bishop nearby.
retractEntity(session, attacker);
spawnPiece(session, "rook", attackerColor, targetPos);
//
// Using engine.spawnPiece — NOT a local helper — so every active
// preset's onPieceSpawn runs on the new pieces. This is what
// fixes the latent "queen-splits spawns pieces without HP" bug
// we used to have: piece-hp now seeds Hp=2 on the fissioned
// rook and bishop via onPieceSpawn, without queen-splits needing
// to know HP exists.
retractEntity(engine, attacker);
engine.spawnPiece("rook", attackerColor, targetPos, {
reason: "fission",
hasMoved: true,
});
// Find the first empty adjacent square clockwise from N and spawn
// the bishop there. If all 8 are occupied (rare — usually happens
@ -152,7 +147,10 @@ PRESET_REGISTRY.register({
if (f < 0 || f > 7 || r < 0 || r > 7) continue;
const sq = squareOf(f, r) as Square;
if (pieceAtSquare(session, sq) !== null) continue;
spawnPiece(session, "bishop", attackerColor, sq);
engine.spawnPiece("bishop", attackerColor, sq, {
reason: "fission",
hasMoved: true,
});
break;
}

View file

@ -47,6 +47,7 @@
import type { EntityId } from "@paratype/rete";
import type { ChessEngine, GameResult } from "../engine.js";
import type { LegalMove } from "../rules/types.js";
import type { ChessAttrKey } from "../schema.js";
/** Return shape for onBeforeCapture. `consume: true` skips the engine's
* default capture path (no target retraction, no attacker move).
@ -56,12 +57,23 @@ export interface CaptureHookResult {
}
/**
* Describes WHERE a unit of damage is coming from. Presets that want
* to react only to certain damage sources (e.g. a hypothetical
* "poison-resistant" preset that ignores damage of kind "poison") read
* `ctx.kind`. The engine sets `attacker` on direct hits; damage with no
* attacking entity (poisoned-squares tick, fall damage, etc) leaves it
* undefined.
* Context for `onBeforeCapture`. Fired when a capture is about to
* resolve — presets that want to replace the default retract+advance
* with their own mechanic (queen-splits fission, explosive-rook AoE,
* capture-to-win winner-recording) read this and return
* `{ consume: true }`.
*/
export interface CaptureHookContext {
readonly engine: ChessEngine;
readonly attacker: EntityId;
readonly target: EntityId;
readonly mover: "white" | "black";
}
/**
* Describes WHERE a unit of damage is coming from. Passed to
* `engine.dealDamage` by the caller; bundled into `DamageHookContext`
* for the `onDamage` hook.
*
* `kind` is typed as a string union with known values plus free-form
* overflow so future presets can introduce new damage kinds without
@ -73,6 +85,164 @@ export interface DamageContext {
readonly attacker?: EntityId;
}
/**
* Full context passed to `onDamage` hooks. Bundles the target entity,
* the amount being dealt, and the DamageContext source tag into one
* growable object.
*
* Future fields (move being executed, board position snapshot,
* turn number, …) can be added without breaking existing hook
* implementations — they'll simply ignore the new fields.
*/
export interface DamageHookContext {
readonly engine: ChessEngine;
readonly target: EntityId;
readonly amount: number;
readonly kind: DamageContext["kind"];
readonly attacker?: EntityId;
}
/**
* Base shape inherited by every hook context. Carrying the engine
* on every context means presets don't need to remember "was it
* the first arg this time or the third?"
*/
export interface HookContext {
readonly engine: ChessEngine;
}
/**
* Context for lifecycle hooks that don't carry per-event data —
* `onActivate`, `onDeactivate`. Keeps the extension point ready if
* we later need to add "was this fired as part of a save-load
* restoration?" or similar fields without breaking every preset.
*
* Currently identical to `HookContext`; aliased (not extended) to
* satisfy the no-empty-interface lint rule while keeping the type
* name semantically distinct at call sites.
*/
export type LifecycleContext = HookContext;
/**
* Context for `onAfterMove`. `mover` is the color that just moved.
*/
export interface MoveHookContext extends HookContext {
readonly mover: "white" | "black";
}
/**
* Context for `onBeforeMove`. Fires AFTER move legality is confirmed
* but BEFORE any mutation. Presets may inspect the move + read state,
* then return `{ cancel: true, reason }` to abort. Returning anything
* else (undefined, `{ cancel: false }`) lets the move proceed.
*
* NOTE: using `cancel` here is a deliberately strong capability. It
* lets a preset veto a move the engine considers legal — e.g., a
* "pawn-stamina" preset that blocks pushes when stamina is empty.
* Presets MUST supply a human-readable `reason` so the UI can
* explain the block via toast.
*/
export interface BeforeMoveContext extends HookContext {
readonly mover: "white" | "black";
readonly pieceId: EntityId;
readonly from: number;
readonly to: number;
readonly isCapture: boolean;
}
/**
* Return shape for `onBeforeMove`. Presets that don't want to veto
* can skip implementing the hook entirely; those that do must
* provide a human-readable `reason` when cancelling.
*/
export interface BeforeMoveResult {
readonly cancel?: boolean;
readonly reason?: string;
}
/**
* Context for `onTurnStart`. Fires AFTER the turn counter has flipped
* (Turn fact updated) and AFTER `onAfterMove`, but BEFORE the side-
* to-move's legal-move list is requested. Ideal hook for:
* - regenerating per-piece resources (Stamina +1 up to max)
* - decrementing cooldown timers
* - refreshing auras / blessings on altar squares
*/
export interface TurnStartContext extends HookContext {
/** The color whose turn is now beginning. */
readonly turn: "white" | "black";
}
/**
* Context for `describeMoveEffect`. Carries the raw move payload,
* capture info, and mover color — enough for presets to decide
* whether they contributed to this move and how to describe it.
*
* Separate from `MoveHookContext` because we explicitly DON'T pass
* the full `MoveRecord` being built — circular references make
* serialization awkward, and the hook is narrow enough that a few
* fields are easier to document than "the record so far".
*/
export interface DescribeMoveEffectContext extends HookContext {
readonly mover: "white" | "black";
readonly from: number;
readonly to: number;
readonly movingType: string;
readonly capturedType: string | null;
readonly isEnPassant: boolean;
readonly isCastling: boolean;
readonly promotion: string | null;
}
/**
* Context for `onCheckGameResult` — fired when the engine is deciding
* the game's terminal state. Presets that want to override the default
* checkmate/stalemate/draw logic read this and return a verdict.
*
* Aliased (not extended) to satisfy no-empty-interface lint while
* preserving the named type at call sites for readability.
*/
export type GameResultHookContext = HookContext;
/**
* Context for `shouldFilterSelfCheck`. `color` is whose moves are
* being generated — a preset scoped to white would typically only
* opt out of the filter when `color === "white"`.
*/
export interface SelfCheckFilterContext extends HookContext {
readonly color: "white" | "black";
}
/**
* Why a piece is being spawned. Used by `onPieceSpawn` hooks to
* decide whether to participate (e.g., a preset that resurrects
* captured pieces shouldn't stack its own `onPieceSpawn` into its
* own resurrection path). `string & {}` lets new reasons enter the
* union without editing this file — each preset documents the kinds
* it emits.
*/
export type PieceSpawnReason =
| "initial" // from generateStartingPosition at engine construction
| "promotion" // pawn reached last rank
| "fission" // queen-splits spawning rook + bishop
| "summon" // generic / preset-authored
| "resurrection" // piece brought back from the dead
| (string & {});
/**
* Context passed to `onPieceSpawn`. Carries everything a hook might
* need to tag the new entity (seed HP, mark with shield, register it
* in preset state, …) without needing to re-query the session.
*/
export interface PieceSpawnContext {
readonly engine: ChessEngine;
readonly pieceId: EntityId;
readonly type: string; // PieceType, kept as string for forward-compat with custom types
readonly color: "white" | "black";
readonly square: number; // Square
readonly reason: PieceSpawnReason;
}
/**
* Return shape for onDamage. Semantics:
* - `consume: true` means "I'm the authority on this damage event;
@ -104,6 +274,25 @@ export interface PresetDef {
/** Preset IDs that must also be active for this one to be valid. */
readonly requires: readonly string[];
/**
* Per-piece attributes OWNED by this preset. When the preset is
* active, the engine treats these as part of every piece's identity:
* - retracted when the piece dies (default damage path)
* - seeded on newly spawned pieces via `onPieceSpawn` if this
* preset implements that hook
* - included in save-state serialization
*
* `Hp` is the canonical example — declared by `piece-hp` rather than
* being hardcoded in core. This makes attribute-carrying presets
* (Shield, Armor, Stamina, Mana, …) a purely additive surface.
*
* Attributes must already exist in `ChessAttrMap` — we don't allow
* free-form keys, because fact-type safety depends on the exhaustive
* attribute map. Adding a new attribute = one-line edit to schema.ts
* + declaration here.
*/
readonly pieceAttributes?: readonly ChessAttrKey[];
// ── Move-generation hooks ────────────────────────────────────────────
readonly getExtraMoves?: (engine: ChessEngine, pieceId: EntityId) => LegalMove[];
readonly filterMoves?: (
@ -113,14 +302,12 @@ export interface PresetDef {
) => LegalMove[];
// ── Lifecycle hooks ──────────────────────────────────────────────────
readonly onActivate?: (engine: ChessEngine) => void;
readonly onDeactivate?: (engine: ChessEngine) => void;
readonly onActivate?: (ctx: LifecycleContext) => void;
readonly onDeactivate?: (ctx: LifecycleContext) => void;
// ── Capture-interception hook ────────────────────────────────────────
readonly onBeforeCapture?: (
engine: ChessEngine,
attacker: EntityId,
target: EntityId,
ctx: CaptureHookContext,
) => CaptureHookResult | void;
/**
@ -147,12 +334,42 @@ export interface PresetDef {
* is the canonical implementer.
*/
readonly onDamage?: (
engine: ChessEngine,
target: EntityId,
amount: number,
ctx: DamageContext,
ctx: DamageHookContext,
) => DamageHookResult | void;
/**
* Contribute a human-readable summary of what this preset did on
* the move that just resolved. Returning a non-empty string appends
* `{ presetId, summary }` to the MoveRecord's `presetEffects` array
* — surfaced by UI move-list panels, PGN export annotations, etc.
*
* Return `undefined` (or omit the hook) when the preset had no
* effect on this move. The hook fires even when the preset DIDN'T
* intercept a hook — most presets will read the context to decide
* whether to contribute (e.g. queen-splits only contributes when
* the moving piece was a queen that captured).
*
* Fires AFTER all mutations are applied but BEFORE `onAfterMove`.
*/
readonly describeMoveEffect?: (
ctx: DescribeMoveEffectContext,
) => string | undefined;
/**
* Fires when a new piece entity is created via `engine.spawnPiece`.
* Every active preset gets a chance to tag the new piece — seed
* `Hp`, mark it with `Shield`, record it in preset state, etc.
*
* Runs AFTER the core attrs (PieceType, Color, Position, HasMoved)
* are inserted, so presets can read the piece's identity.
*
* This is how `piece-hp` composes with any spawn-emitting preset
* (queen-splits, promotion, resurrection) without those presets
* knowing HP exists: they call `engine.spawnPiece(...)` and HP
* gets seeded automatically via this hook.
*/
readonly onPieceSpawn?: (ctx: PieceSpawnContext) => void;
/**
* Fires after every successful `applyMove`, after turn advancement
* and tickAfterMove but before checkGameResult. `moverColor` is the
@ -167,10 +384,7 @@ export interface PresetDef {
* wants to affect the non-mover; poisoned-squares damages the
* mover).
*/
readonly onAfterMove?: (
engine: ChessEngine,
moverColor: "white" | "black",
) => void;
readonly onAfterMove?: (ctx: MoveHookContext) => void;
/**
* Hook into terminal-position detection. Return a concrete `GameResult`
@ -183,7 +397,7 @@ export interface PresetDef {
* `last-piece-standing` (annihilation replaces checkmate), which both
* redefine "when is the game over".
*/
readonly onCheckGameResult?: (engine: ChessEngine) => GameResult | undefined;
readonly onCheckGameResult?: (ctx: GameResultHookContext) => GameResult | undefined;
/**
* Opt out of the engine's default self-check filter for moves of
@ -202,9 +416,40 @@ export interface PresetDef {
* legally survive being attacked.
*/
readonly shouldFilterSelfCheck?: (
engine: ChessEngine,
color: "white" | "black",
ctx: SelfCheckFilterContext,
) => boolean | undefined;
/**
* Phase hook: fires AFTER the move has been confirmed legal but
* BEFORE any state mutation. Return `{ cancel: true, reason }` to
* abort the move — the engine treats the attempt as rejected and
* surfaces `reason` via a toast.
*
* Used by resource-tracking presets (stamina, action-points,
* cooldowns). Also the ONLY hook that can block an otherwise
* legal move, which is why it requires an explicit `reason`.
*
* Scope-aware: fires only for presets whose scope covers the
* mover's color (a `scope=white` preset doesn't veto black's
* moves).
*/
readonly onBeforeMove?: (
ctx: BeforeMoveContext,
) => BeforeMoveResult | void;
/**
* Phase hook: fires AFTER the turn has flipped and AFTER
* `onAfterMove`, but BEFORE the new side's legal moves are
* computed.
*
* This is the canonical place to regenerate per-piece resources,
* tick cooldowns, refresh auras, or any "start of turn" logic
* that should take effect BEFORE the player sees their options.
*
* Scope-aware: fires only for presets whose scope covers the
* color whose turn is beginning.
*/
readonly onTurnStart?: (ctx: TurnStartContext) => void;
}
/**

View file

@ -0,0 +1,97 @@
/**
* Shared helpers for preset tests.
*
* Four preset test files used to each define their own copies of
* `pieceAt`, `hpOf`, `typeOf`, and `clearBoard`. This module
* centralizes them so new preset tests can import rather than
* copy-paste.
*
* Intentionally named `test-utils.ts` (not `.test.ts`) so vitest
* doesn't mistake it for a test file.
*/
import { ChessEngine } from "../engine.js";
import type { EntityId } from "@paratype/rete";
import { algebraicToSquare } from "../coord.js";
/** Look up the piece entity on a given algebraic square, if any. */
export function pieceAt(
engine: ChessEngine,
square: string,
): EntityId | null {
const target = algebraicToSquare(square);
for (const f of engine.session.allFacts()) {
if (f.attr === "Position" && f.value === target) return f.id;
}
return null;
}
/** Read the Hp attribute of a piece. Null when Hp isn't set. */
export function hpOf(engine: ChessEngine, id: EntityId): number | null {
if (!engine.session.contains(id, "Hp")) return null;
return engine.session.get(id, "Hp") as number;
}
/** Read the PieceType of an entity. Null if retracted. */
export function typeOf(engine: ChessEngine, id: EntityId): string | null {
if (!engine.session.contains(id, "PieceType")) return null;
return engine.session.get(id, "PieceType") as string;
}
/** True if the entity still has a PieceType fact (not retracted). */
export function exists(engine: ChessEngine, id: EntityId): boolean {
return engine.session.contains(id, "PieceType");
}
/**
* Retract every non-king piece on the board so tests can build
* minimal positions from scratch without FIDE starting-position
* noise. Kings are preserved by default because check-detection
* assumes their presence; pass `preserveKings: false` to wipe them
* too (useful for testing custom-piece-type variants).
*
* Uses `engine.effectivePieceAttrs` so preset-declared attributes
* (Hp, Shield, …) are cleaned up too — no zombie facts.
*/
export function clearBoard(
engine: ChessEngine,
opts: { readonly preserveKings?: boolean } = {},
): void {
const preserveKings = opts.preserveKings ?? true;
const facts = engine.session.allFacts();
const toClear: EntityId[] = [];
for (const f of facts) {
if (f.attr !== "PieceType") continue;
if ((f.id as number) <= 0) continue;
if (preserveKings && f.value === "king") continue;
toClear.push(f.id);
}
for (const id of toClear) {
for (const attr of engine.effectivePieceAttrs) {
if (engine.session.contains(id, attr)) engine.session.retract(id, attr);
}
}
}
/**
* Place a piece on `square` directly via session inserts. Bypasses
* `engine.spawnPiece` intentionally — tests that want to verify
* spawn-hook behavior should call `engine.spawnPiece` explicitly.
* This helper is for scaffolding board positions where spawn hooks
* are irrelevant (or need to be avoided, as in "no-HP-seeded test
* piece").
*/
export function placePiece(
engine: ChessEngine,
type: string,
color: "white" | "black",
square: string | number,
opts: { readonly hasMoved?: boolean } = {},
): EntityId {
const id = engine.session.nextId();
const sq = typeof square === "string" ? algebraicToSquare(square) : square;
engine.session.insert(id, "PieceType", type);
engine.session.insert(id, "Color", color);
engine.session.insert(id, "Position", sq);
engine.session.insert(id, "HasMoved", opts.hasMoved ?? false);
return id;
}

View file

@ -0,0 +1,128 @@
/**
* Tests for `ChessEngine.emitEffect` + `subscribeEffects` and the
* presets that emit effects via those APIs.
*/
import { describe, it, expect, vi } from "vitest";
import "./index.js";
import { ChessEngine, type VisualEffect } from "../engine.js";
import { algebraicToSquare } from "../coord.js";
import type { EntityId } from "@paratype/rete";
describe("engine.emitEffect + subscribeEffects", () => {
it("subscribers receive every emitted effect", () => {
const engine = new ChessEngine();
const received: VisualEffect[] = [];
engine.subscribeEffects((e) => received.push(e));
engine.emitEffect({ kind: "test", square: 0, ttl: 100 });
engine.emitEffect({ kind: "other", square: 5, ttl: 200 });
expect(received).toHaveLength(2);
expect(received[0]?.kind).toBe("test");
expect(received[1]?.kind).toBe("other");
});
it("unsubscribe stops further deliveries", () => {
const engine = new ChessEngine();
const received: VisualEffect[] = [];
const unsub = engine.subscribeEffects((e) => received.push(e));
engine.emitEffect({ kind: "a", square: null, ttl: 100 });
unsub();
engine.emitEffect({ kind: "b", square: null, ttl: 100 });
expect(received).toHaveLength(1);
});
it("multiple subscribers all receive the same effect", () => {
const engine = new ChessEngine();
const a: VisualEffect[] = [];
const b: VisualEffect[] = [];
engine.subscribeEffects((e) => a.push(e));
engine.subscribeEffects((e) => b.push(e));
engine.emitEffect({ kind: "x", square: 0, ttl: 100 });
expect(a).toHaveLength(1);
expect(b).toHaveLength(1);
});
it("a subscriber that throws doesn't break other subscribers", () => {
const engine = new ChessEngine();
const survivor: VisualEffect[] = [];
const errSpy = vi.spyOn(console, "error").mockImplementation(() => {});
engine.subscribeEffects(() => {
throw new Error("boom");
});
engine.subscribeEffects((e) => survivor.push(e));
engine.emitEffect({ kind: "x", square: 0, ttl: 100 });
expect(survivor).toHaveLength(1);
errSpy.mockRestore();
});
it("no subscribers is a no-op (no throw)", () => {
const engine = new ChessEngine();
expect(() =>
engine.emitEffect({ kind: "x", square: 0, ttl: 100 }),
).not.toThrow();
});
});
describe("explosive-rook emits 'explosion' effect", () => {
it("fires on rook capture with target square", () => {
const engine = new ChessEngine();
// Minimal setup: clear board, add white rook on a1, black pawn on a5
const facts = engine.session.allFacts();
for (const f of facts) {
if (f.attr !== "PieceType") continue;
if ((f.id as number) <= 0) continue;
if (f.value === "king") continue;
for (const attr of ["PieceType", "Color", "Position", "HasMoved", "Hp"] as const) {
if (engine.session.contains(f.id, attr)) engine.session.retract(f.id, attr);
}
}
const rook: EntityId = engine.session.nextId();
engine.session.insert(rook, "PieceType", "rook");
engine.session.insert(rook, "Color", "white");
engine.session.insert(rook, "Position", algebraicToSquare("a1"));
const target: EntityId = engine.session.nextId();
engine.session.insert(target, "PieceType", "pawn");
engine.session.insert(target, "Color", "black");
engine.session.insert(target, "Position", algebraicToSquare("a5"));
engine.session.insert(target, "HasMoved", true);
engine.setActivePresets([
{ id: "explosive-rook", scope: "both", turnsRemaining: null },
]);
const received: VisualEffect[] = [];
engine.subscribeEffects((e) => received.push(e));
const capture = engine.findMove(
algebraicToSquare("a1"),
algebraicToSquare("a5"),
);
expect(capture).not.toBeNull();
engine.applyMove(capture!);
const explosion = received.find((e) => e.kind === "explosion");
expect(explosion).toBeDefined();
expect(explosion?.square).toBe(algebraicToSquare("a5"));
expect(explosion?.ttl).toBeGreaterThan(0);
});
});
describe("king-heals emits 'heal' effect", () => {
it("fires on successful regen with king square", () => {
const engine = new ChessEngine();
engine.setActivePresets([
{ id: "piece-hp", scope: "both", turnsRemaining: null },
{ id: "king-heals", scope: "both", turnsRemaining: null },
]);
const received: VisualEffect[] = [];
engine.subscribeEffects((e) => received.push(e));
// 1. e4 — heals BLACK king (non-mover). Black king on e8, Hp=2 → 3.
engine.applyMove(engine.findMove(algebraicToSquare("e2"), algebraicToSquare("e4"))!);
const heal = received.find((e) => e.kind === "heal");
expect(heal).toBeDefined();
expect(heal?.square).toBe(algebraicToSquare("e8"));
});
});

View file

@ -3,19 +3,70 @@
* When a capture occurs, the captured piece's facts are retracted from WM.
*/
import type { Session, EntityId } from "@paratype/rete";
import type { PieceColor } from "../schema.js";
/** All known chess fact attributes for a piece entity.
* Exported so presets and the damage pipeline can stay in lockstep
* without each duplicating the list. */
export const PIECE_ATTRS = ["PieceType", "Color", "Position", "HasMoved", "Hp"] as const;
import type { ChessAttrKey, PieceColor } from "../schema.js";
/**
* Apply a capture: retract all known facts for the captured piece.
* Called after confirming the capture is legal.
* FIDE-minimal attributes every piece entity carries.
*
* This is the CORE list — preset-specific attributes (`Hp`, `Shield`,
* `Stamina`, …) are declared by presets via `PresetDef.pieceAttributes`
* and unioned in at runtime via `ChessEngine.effectivePieceAttrs`.
* Callers that need the ENGINE-AWARE list (retract-on-death, save-state
* serialization, etc.) should read `engine.effectivePieceAttrs`; this
* constant is only for pure-function / no-engine contexts (e.g. the
* `applyCapture` helper below used by legacy tests).
*/
export const CORE_PIECE_ATTRS: readonly ChessAttrKey[] = [
"PieceType",
"Color",
"Position",
"HasMoved",
] as const;
/**
* Attributes that live on the game entity (id 0), NOT on pieces.
*
* Used by pure-function helpers (check / stalemate / turn what-if
* simulators) to filter facts when snapshotting a session for
* simulation. Anything on an id > 0 that ISN'T in this list is
* treated as a piece attribute — which means preset-declared attrs
* like `Hp` / `Shield` are automatically picked up by the simulator
* without requiring an engine reference.
*
* The alternative would be to thread an engine reference through
* every pure simulation helper. This keeps those helpers simple at
* the cost of one extra list to maintain — a reasonable tradeoff
* because new game-level attrs are rare (`Turn`, `EnPassantTarget`,
* `HalfmoveClock`, `FullmoveNumber`, `GameStatus`, `Winner`).
*/
export const GAME_LEVEL_ATTRS: readonly ChessAttrKey[] = [
"Turn",
"HalfmoveClock",
"FullmoveNumber",
"EnPassantTarget",
"GameStatus",
"Winner",
] as const;
/**
* Is `attr` an attribute of a piece (as opposed to the game entity)?
* Used by session-snapshot helpers to know what to copy.
*/
export function isPieceAttr(attr: string): attr is ChessAttrKey {
return !(GAME_LEVEL_ATTRS as readonly string[]).includes(attr);
}
/**
* Apply a capture: retract all core attrs for the captured piece.
*
* LEGACY helper — the live engine uses `engine.dealDamage` + the
* dynamic attribute list so preset attributes are cleaned up too.
* This function remains for the capture.test.ts tests that construct
* a raw `Session` without a `ChessEngine`. For those tests no presets
* can be active, so the core list is sufficient.
*/
export function applyCapture(session: Session, capturedId: EntityId): void {
for (const attr of PIECE_ATTRS) {
for (const attr of CORE_PIECE_ATTRS) {
if (session.contains(capturedId, attr)) {
session.retract(capturedId, attr);
}

View file

@ -29,69 +29,14 @@ import { Session } from "@paratype/rete";
import type { EntityId } from "@paratype/rete";
import type { PieceColor, PieceType, Square } from "../schema.js";
import { oppositeColor } from "../schema.js";
import { getLegalKnightMoves } from "./knight.js";
import {
getLegalRookMoves,
getLegalBishopMoves,
getLegalQueenMoves,
} from "./sliding.js";
import { getLegalKingMoves } from "./king.js";
import { pawnCaptureSqares } from "./primitives.js";
import { isPieceAttr } from "./capture.js";
import type { LegalMove } from "./types.js";
import { getPiecePosition } from "./board-queries.js";
type MoveGetter = (session: Session, pieceId: EntityId) => LegalMove[];
/**
* Per-piece-type "does this piece attack `target`?" predicate.
*
* For everything except pawns we can reuse the piece's legal-move
* generator — if a legal move lands on `target`, the piece attacks it.
*
* Pawns need special handling: `getLegalPawnMoves` only yields diagonal
* captures when an enemy currently occupies the diagonal, but for check
* detection we need the *attack geometry* (the squares the pawn would
* capture on, regardless of what's there). A king cannot step onto a
* pawn's diagonal even when that square is empty.
*/
type AttackProbe = (session: Session, pieceId: EntityId, target: Square) => boolean;
function movesAttackProbe(getter: MoveGetter): AttackProbe {
return (session, pieceId, target) => {
for (const m of getter(session, pieceId)) {
if (m.to === target) return true;
}
return false;
};
}
const ATTACK_PROBES: Record<PieceType, AttackProbe> = {
pawn: (session, pieceId, target) => {
const from = getPiecePosition(session, pieceId);
if (from === null) return false;
const colorVal = session.get(pieceId, "Color");
if (colorVal === undefined) return false;
const color = colorVal as PieceColor;
for (const sq of pawnCaptureSqares(from, color)) {
if (sq === target) return true;
}
return false;
},
knight: movesAttackProbe(getLegalKnightMoves),
bishop: movesAttackProbe(getLegalBishopMoves),
rook: movesAttackProbe(getLegalRookMoves),
queen: movesAttackProbe(getLegalQueenMoves),
king: movesAttackProbe(getLegalKingMoves),
};
/** Attributes we copy when snapshotting a session for "what-if" analysis. */
const PIECE_ATTRS = [
"PieceType",
"Color",
"Position",
"HasMoved",
"Hp",
] as const;
import { PIECE_TYPE_REGISTRY } from "../presets/piece-type-registry.js";
// Side-effect: ensure FIDE piece types are registered. Tests that
// exercise these pure-function helpers directly (without ChessEngine)
// wouldn't otherwise trigger the registry population from
// `presets/index.ts`.
import "../presets/core-piece-types.js";
/**
* Is `square` attacked by any piece of `byColor`?
@ -118,10 +63,12 @@ export function isSquareAttacked(
if (typeFact === undefined) continue;
const type = typeFact.value as PieceType;
const probe = ATTACK_PROBES[type];
if (probe === undefined) continue;
if (probe(session, f.id, square)) return true;
// Custom piece types register their own attack probe via the
// piece-type registry. Unknown types (degenerate) contribute no
// attacks.
const def = PIECE_TYPE_REGISTRY.get(type);
if (def === undefined) continue;
if (def.attackProbe(session, f.id, square)) return true;
}
return false;
}
@ -165,10 +112,13 @@ export function isInCheck(session: Session, color: PieceColor): boolean {
function snapshotSession(session: Session): Session {
const temp = new Session({ autoFire: false });
for (const f of session.allFacts()) {
// Only copy attrs we care about for board geometry + check detection.
if ((PIECE_ATTRS as readonly string[]).includes(f.attr)) {
temp.insert(f.id, f.attr, f.value);
}
// Skip game-level facts (Turn, EnPassantTarget, etc) — the
// simulator only cares about board geometry + whatever custom
// piece attrs presets have added. Piece entities have id > 0 by
// convention.
if ((f.id as number) <= 0) continue;
if (!isPieceAttr(f.attr)) continue;
temp.insert(f.id, f.attr, f.value);
}
return temp;
}
@ -182,7 +132,13 @@ function clearSquare(temp: Session, square: Square): void {
const occupant = facts.find(f => f.attr === "Position" && f.value === square);
if (occupant === undefined) return;
const id = occupant.id;
for (const attr of PIECE_ATTRS) {
// Retract every piece-level fact on this id. Using allFacts()-based
// enumeration rather than a hardcoded attr list so preset-declared
// attributes (Hp, Shield, …) are also cleaned.
const toRetract = facts
.filter(f => f.id === id && isPieceAttr(f.attr))
.map(f => f.attr);
for (const attr of toRetract) {
if (temp.contains(id, attr)) temp.retract(id, attr);
}
}

View file

@ -21,34 +21,13 @@
* - En passant as an escape. En-passant generation is P2.16; once it
* lands, it can be plumbed in by extending MOVE_GETTERS.
*/
import type { Session, EntityId } from "@paratype/rete";
import type { Session } from "@paratype/rete";
import type { PieceColor, PieceType } from "../schema.js";
import { isInCheck, filterSelfCheckMoves } from "./check.js";
import { getLegalPawnMoves } from "./pawn.js";
import { getLegalKnightMoves } from "./knight.js";
import {
getLegalRookMoves,
getLegalBishopMoves,
getLegalQueenMoves,
} from "./sliding.js";
import { getLegalKingMoves } from "./king.js";
import type { LegalMove } from "./types.js";
type MoveGetter = (session: Session, pieceId: EntityId) => LegalMove[];
/**
* Dispatch table mapping PieceType → its pseudo-legal move generator.
* "Pseudo-legal" = respects piece geometry + blockers but ignores
* self-check; the self-check filter handles that afterwards.
*/
const MOVE_GETTERS: Record<PieceType, MoveGetter> = {
pawn: getLegalPawnMoves,
knight: getLegalKnightMoves,
bishop: getLegalBishopMoves,
rook: getLegalRookMoves,
queen: getLegalQueenMoves,
king: getLegalKingMoves,
};
import { PIECE_TYPE_REGISTRY } from "../presets/piece-type-registry.js";
// Side-effect: see check.ts comment.
import "../presets/core-piece-types.js";
/**
* Collect every pseudo-legal move for every piece of `color`.
@ -74,8 +53,11 @@ function getAllPseudoLegalMoves(
if (typeFact === undefined) continue;
const type = typeFact.value as PieceType;
const getter = MOVE_GETTERS[type];
if (getter === undefined) continue;
// Dispatch via the piece-type registry — custom types registered
// by presets get their moves collected here too.
const def = PIECE_TYPE_REGISTRY.get(type);
if (def === undefined) continue;
const getter = def.moveGenerator;
for (const m of getter(session, f.id)) {
moves.push(m);

View file

@ -25,35 +25,10 @@ import { Session as ReteSession } from "@paratype/rete";
import type { Session, EntityId } from "@paratype/rete";
import type { PieceColor, PieceType } from "../schema.js";
import { isInCheck } from "./check.js";
import { getLegalPawnMoves } from "./pawn.js";
import { getLegalKnightMoves } from "./knight.js";
import {
getLegalRookMoves,
getLegalBishopMoves,
getLegalQueenMoves,
} from "./sliding.js";
import { getLegalKingMoves } from "./king.js";
import type { LegalMove } from "./types.js";
type MoveGetter = (session: Session, pieceId: EntityId) => LegalMove[];
const MOVE_GETTERS: Record<PieceType, MoveGetter> = {
pawn: getLegalPawnMoves,
knight: getLegalKnightMoves,
bishop: getLegalBishopMoves,
rook: getLegalRookMoves,
queen: getLegalQueenMoves,
king: getLegalKingMoves,
};
/** Attributes we copy when snapshotting a session for "what-if" analysis. */
const PIECE_ATTRS = [
"PieceType",
"Color",
"Position",
"HasMoved",
"Hp",
] as const;
import { isPieceAttr } from "./capture.js";
import { PIECE_TYPE_REGISTRY } from "../presets/piece-type-registry.js";
// Side-effect: see check.ts comment.
import "../presets/core-piece-types.js";
/**
* Does `color` have at least one move that doesn't leave its king in
@ -74,14 +49,18 @@ function hasAnyLegalMove(session: Session, color: PieceColor): boolean {
}
for (const piece of pieces) {
const getter = MOVE_GETTERS[piece.type];
const getter = PIECE_TYPE_REGISTRY.get(piece.type)?.moveGenerator;
if (getter === undefined) continue;
for (const move of getter(session, piece.id)) {
// Build a what-if session with only the piece-geometry attrs.
// Build a what-if session with only piece-level attrs (game-level
// facts are irrelevant for legality). Any attr that isn't
// game-level — including preset-declared ones like Hp / Shield —
// is carried forward automatically.
const temp = new ReteSession({ autoFire: false });
for (const f of facts) {
if (!(PIECE_ATTRS as readonly string[]).includes(f.attr)) continue;
if ((f.id as number) <= 0) continue;
if (!isPieceAttr(f.attr)) continue;
// For captures, drop whatever sits on the destination square.
if (move.isCapture && f.attr === "Position" && f.value === move.to) {
continue;
@ -89,13 +68,17 @@ function hasAnyLegalMove(session: Session, color: PieceColor): boolean {
temp.insert(f.id, f.attr, f.value);
}
// For captures we also need to clear the captured piece's other
// attrs (PieceType, Color, ...). Easiest: retract by id.
// attrs (PieceType, Color, ...). Retract by id — enumerate the
// target's piece-level facts rather than a hardcoded list.
if (move.isCapture) {
const captured = facts.find(
g => g.attr === "Position" && g.value === move.to && g.id !== move.pieceId,
);
if (captured !== undefined) {
for (const attr of PIECE_ATTRS) {
const attrs = facts
.filter(g => g.id === captured.id && isPieceAttr(g.attr))
.map(g => g.attr);
for (const attr of attrs) {
if (temp.contains(captured.id, attr)) {
temp.retract(captured.id, attr);
}

View file

@ -66,14 +66,9 @@ export function clearMoveGeneratorRegistry(): void {
moveGeneratorRegistry.clear();
}
/** Piece-level attributes retracted when an entity is captured. */
const PIECE_ATTRS = [
"PieceType",
"Color",
"Position",
"HasMoved",
"Hp",
] as const;
// Snapshot-copy predicate shared with check.ts / stalemate.ts.
// See capture.ts for the "not game-level" rationale.
import { isPieceAttr } from "./capture.js";
/**
* Get every legal move available to pieces of `color` given the current
@ -148,7 +143,15 @@ export function applyMove(session: Session, move: LegalMove): void {
if (move.isCapture) {
const capturedId = getPieceAt(session, move.to);
if (capturedId !== null && capturedId !== move.pieceId) {
for (const attr of PIECE_ATTRS) {
// Enumerate the captured piece's attrs from the session rather
// than from a hardcoded list — preset-declared attrs (Hp,
// Shield, …) get cleaned up too without this function needing
// to know about presets.
const attrs = session
.allFacts()
.filter(f => f.id === capturedId && isPieceAttr(f.attr))
.map(f => f.attr);
for (const attr of attrs) {
if (session.contains(capturedId, attr)) {
session.retract(capturedId, attr);
}

View file

@ -17,6 +17,18 @@ export type GameResult = PieceColor | "draw";
/** EntityId reserved for game-level facts (Turn, HalfmoveClock, etc.). */
export const GAME_ENTITY: EntityId = 0 as EntityId;
/**
* Reserved EntityId for preset-state facts. Each active preset can
* stash typed, per-game state on this entity via
* `ChessEngine.presetState(presetId)` — attributes are namespaced by
* preset id to prevent collisions.
*
* Using a negative id keeps preset-state facts out of the "id > 0 is
* a piece" convention used throughout the codebase. Session.nextId()
* starts at 1, so -1 can never collide.
*/
export const PRESET_STATE_ENTITY: EntityId = -1 as EntityId;
/**
* Maps attribute name to its TypeScript type.
* Used for typed fact construction and WM queries.

View file

@ -2,6 +2,7 @@ import { useState, useMemo } from 'react';
import type { ChessFact, PieceColor, PieceType } from '../schema';
import { squareToAlgebraic, squareOf, squareColor } from '../coord';
import type { LegalMove } from '../rules/types';
import type { ChessEngine } from '../engine';
import { Piece } from './Piece';
import { AnimatePresence, motion } from 'motion/react';
import { pieceAssets } from '../assets/pieces';
@ -11,6 +12,7 @@ import {
type PieceOverlayComponent,
type SquareOverlayComponent,
} from './preset-overlays';
import { VisualEffectLayer } from './VisualEffectLayer';
import '../presets/ui-overlays-index';
interface BoardProps {
@ -29,6 +31,9 @@ interface BoardProps {
/** Currently-active preset ids. Used to look up registered per-piece
* overlay components (e.g. HP pips for piece-hp). Order preserved. */
activePresetIds?: ReadonlyArray<string>;
/** Live engine reference for the visual effect stream. Optional —
* omit in tests or headless renders; no effects will render. */
engine?: ChessEngine;
}
interface PieceState {
@ -37,7 +42,7 @@ interface PieceState {
color: PieceColor;
}
export function Board({ facts, legalMoves, onMove, turn, myColor, lastMove, checkedKingSquare, activePresetIds }: BoardProps) {
export function Board({ facts, legalMoves, onMove, turn, myColor, lastMove, checkedKingSquare, activePresetIds, engine }: BoardProps) {
// Pre-compute overlay components once per render — lookup is cheap
// but doing it once in a useMemo keeps the Piece render path clean.
const overlays: PieceOverlayComponent[] = useMemo(
@ -351,6 +356,7 @@ export function Board({ facts, legalMoves, onMove, turn, myColor, lastMove, chec
<div className="grid grid-cols-8 grid-rows-8 w-full max-w-2xl mx-auto rounded shadow-[0_20px_40px_-20px_rgba(0,0,0,0.3),_0_4px_8px_-2px_rgba(0,0,0,0.1)] bg-neutral-900 border-4 border-neutral-800">
{squares}
</div>
{engine !== undefined && <VisualEffectLayer engine={engine} />}
<AnimatePresence>
{promotionMove && (

View file

@ -382,6 +382,7 @@ function GameLayout({
lastMove={lastMove}
checkedKingSquare={checkedKingSquare}
activePresetIds={activations.map((a) => a.id)}
{...(state.engine !== null ? { engine: state.engine } : {})}
/>
{/* Overlay for game over to prevent further interaction visually */}

View file

@ -1,5 +1,6 @@
import type { ChessAttrMap, ChessFact, PieceColor, PieceType } from '../schema';
import { pieceAssets } from '../assets/pieces';
import { PIECE_TYPE_REGISTRY } from '../presets/piece-type-registry';
import {
motion,
useMotionValue,
@ -95,7 +96,12 @@ export function Piece({
onDragStart,
onDragEnd,
}: PieceProps) {
const imgSrc = pieceAssets[color][type];
// Look up asset via the piece-type registry so custom types (Cannon,
// Amazon, etc) render correctly. Fall back to the built-in asset
// map for safety — it's the same data source either way for FIDE
// pieces.
const registryDef = PIECE_TYPE_REGISTRY.get(type);
const imgSrc = registryDef?.assets[color] ?? pieceAssets[color][type];
// Raw pointer offset from drag origin, updated on every `dragover`.
const xRaw = useMotionValue(0);

View file

@ -0,0 +1,152 @@
/**
* Visual effect layer for the chess board.
*
* Subscribes to the engine's effect stream and renders ephemeral
* overlays (explosions, heal shimmers, poison bubbles, …) at the
* appropriate squares. Effects auto-expire after their TTL.
*
* ## Adding a new effect kind
*
* 1. In your preset, call `engine.emitEffect({ kind: "lightning", square, ttl, data })`.
* 2. Register a renderer below in `EFFECT_RENDERERS`. The renderer
* is a React component receiving `(effect: VisualEffect)` and
* returning the overlay JSX.
* 3. Unknown `kind`s fall back to a generic pulse so missing
* renderers are a visual no-op, not a crash.
*
* ## Positioning
*
* The layer is absolutely positioned to fill its parent (the Board
* container). Each effect is positioned within the 8x8 grid using
* `top/left` percentages derived from the square index. `square: null`
* positions the effect as a full-board overlay.
*/
import { cloneElement, useEffect, useState } from "react";
import { AnimatePresence, motion } from "motion/react";
import type { ChessEngine, VisualEffect } from "../engine";
/** An effect plus a unique id so React keys stay stable during TTL. */
interface TaggedEffect {
readonly id: number;
readonly effect: VisualEffect;
}
/**
* Square → {top%, left%} in the 8x8 grid. Uses the same orientation
* as Board.tsx (rank 8 at top, file a at left) — both treat
* `squareOf(file, rank)` identically so this math lines up.
*/
function squareStyle(square: number): { top: string; left: string } {
const file = square % 8;
const rank = Math.floor(square / 8);
// Rank 8 is top (visualRank 0); we invert.
const visualRank = 7 - rank;
return {
top: `${(visualRank * 100) / 8}%`,
left: `${(file * 100) / 8}%`,
};
}
/** Renderer type for a named effect kind. */
type EffectRenderer = (effect: VisualEffect) => React.ReactElement;
const EFFECT_RENDERERS: Record<string, EffectRenderer> = {
explosion: (effect) => (
<motion.div
initial={{ scale: 0.3, opacity: 0.9 }}
animate={{ scale: 2, opacity: 0 }}
transition={{ duration: (effect.ttl ?? 600) / 1000, ease: "easeOut" }}
className="absolute w-[12.5%] aspect-square rounded-full bg-gradient-radial from-orange-300 via-red-500 to-red-900/0"
style={{ ...squareStyle(effect.square ?? 0), mixBlendMode: "screen" }}
data-effect="explosion"
data-effect-square={effect.square ?? ""}
/>
),
heal: (effect) => (
<motion.div
initial={{ scale: 0.8, opacity: 0.8 }}
animate={{ scale: 1.3, opacity: 0 }}
transition={{ duration: (effect.ttl ?? 400) / 1000, ease: "easeOut" }}
className="absolute w-[12.5%] aspect-square rounded-full bg-gradient-radial from-emerald-200 via-emerald-400/60 to-emerald-400/0"
style={{ ...squareStyle(effect.square ?? 0) }}
data-effect="heal"
data-effect-square={effect.square ?? ""}
/>
),
poison: (effect) => (
<motion.div
initial={{ scale: 0.6, opacity: 0.7, y: 4 }}
animate={{ scale: 1.1, opacity: 0, y: -6 }}
transition={{ duration: (effect.ttl ?? 250) / 1000, ease: "easeOut" }}
className="absolute w-[12.5%] aspect-square rounded-full bg-gradient-radial from-fuchsia-300 via-fuchsia-600/60 to-fuchsia-900/0"
style={{ ...squareStyle(effect.square ?? 0) }}
data-effect="poison"
data-effect-square={effect.square ?? ""}
/>
),
};
/** Fallback for effects with no registered renderer. */
function GenericPulse({ effect }: { effect: VisualEffect }) {
return (
<motion.div
initial={{ scale: 0.8, opacity: 0.6 }}
animate={{ scale: 1.4, opacity: 0 }}
transition={{ duration: (effect.ttl ?? 300) / 1000 }}
className="absolute w-[12.5%] aspect-square rounded-full bg-white/50"
style={effect.square !== null ? squareStyle(effect.square) : { inset: 0, width: "100%" }}
data-effect={effect.kind}
data-effect-square={effect.square ?? ""}
/>
);
}
interface VisualEffectLayerProps {
readonly engine: ChessEngine;
}
export function VisualEffectLayer({ engine }: VisualEffectLayerProps) {
const [effects, setEffects] = useState<TaggedEffect[]>([]);
useEffect(() => {
let nextId = 1;
const unsubscribe = engine.subscribeEffects((effect) => {
const tagged: TaggedEffect = { id: nextId++, effect };
setEffects((prev) => [...prev, tagged]);
// Schedule removal after TTL. Using setTimeout with the
// engine's declared TTL — renderers use the same value to
// drive their animation, so DOM removal matches the end of
// the anim.
const timer = window.setTimeout(() => {
setEffects((prev) => prev.filter((e) => e.id !== tagged.id));
}, effect.ttl);
// If the component unmounts before the timer fires, React's
// own unmount path nukes the setTimeout-driven update (the
// component is gone by then). We don't need explicit cleanup.
void timer;
});
return () => {
unsubscribe();
};
}, [engine]);
return (
<div
className="absolute inset-0 pointer-events-none"
data-testid="visual-effect-layer"
>
<AnimatePresence>
{effects.map(({ id, effect }) => {
const renderer = EFFECT_RENDERERS[effect.kind];
const element = renderer !== undefined
? renderer(effect)
: GenericPulse({ effect });
// `cloneElement` with a key is the cleanest way to attach a
// React key to a pre-rendered element so AnimatePresence can
// track mount/unmount. Each tagged effect has a unique id.
return cloneElement(element, { key: id });
})}
</AnimatePresence>
</div>
);
}