test(chess): replay 5 classic FIDE games; Phase 2 acceptance gate (P2.23)

- packages/chess/src/engine.ts — ChessEngine integrates all rule modules
  (pawn, knight, sliding, king, castling, en-passant, promotion, check,
  checkmate, stalemate, draws) into a playable game without the Rete
  production network
- packages/chess/src/pgn.ts — minimal SAN/PGN parser with full
  disambiguation support (file/rank hints, full from-square)
- packages/chess/tests/fide-games/classic-games.test.ts — 5 game tests:
  Fool's Mate, Scholar's Mate, Ruy López, Sicilian Defence, Italian Game

All 5 tests green; typecheck clean.
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Joey Yakimowich-Payne 2026-04-16 15:18:57 -06:00
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/**
* ChessEngine integrates all rule modules into a playable chess game.
*
* Uses Session as working memory; calls rule functions directly (no Rete
* production network that integration is future work).
*/
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";
import {
getCastlingMoves,
applyCastlingMove,
type CastlingMove,
} from "./rules/castling.js";
import {
getEnPassantMoves,
setEnPassantTarget,
clearEnPassantTarget,
applyEnPassantCapture,
} from "./rules/enpassant.js";
import {
isPromotionMove,
applyPromotion,
getPromotionMoves,
} from "./rules/promotion.js";
import {
filterSelfCheckMoves,
isSquareAttacked,
} from "./rules/check.js";
import { isCheckmate } from "./rules/checkmate.js";
import { isStalemate } from "./rules/stalemate.js";
import { isInsufficientMaterial } from "./rules/insufficient.js";
import {
isFiftyMoveDraw,
updateHalfmoveClock,
recordPosition,
isThreefoldRepetition,
} from "./rules/draws.js";
import { applyCapture } from "./rules/capture.js";
import type { LegalMove } from "./rules/types.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,
};
export type GameResult =
| "checkmate"
| "stalemate"
| "draw-50"
| "draw-3fold"
| "draw-insufficient"
| "ongoing";
export class ChessEngine {
public readonly session: Session;
constructor() {
this.session = new Session({ autoFire: false });
generateStartingPosition(this.session);
recordPosition(this.session);
}
getCurrentTurn(): PieceColor {
return (this.session.get(GAME_ENTITY, "Turn") as PieceColor) ?? "white";
}
getAllLegalMoves(): LegalMove[] {
const color = this.getCurrentTurn();
const facts = this.session.allFacts();
const moves: LegalMove[] = [];
const pieces = facts
.filter(f => f.attr === "Color" && f.value === color && (f.id as number) > 0)
.map(f => ({
id: f.id as EntityId,
type: facts.find(t => t.id === f.id && t.attr === "PieceType")
?.value as PieceType,
}))
.filter(p => p.type !== undefined);
for (const piece of pieces) {
const getter = PIECE_MOVE_GETTERS[piece.type];
if (!getter) continue;
let pieceMoves = getter(this.session, piece.id);
// Add en passant for pawns
if (piece.type === "pawn") {
pieceMoves = [
...pieceMoves,
...getEnPassantMoves(this.session, piece.id),
];
}
// Add castling for kings
if (piece.type === "king") {
const enemyColor: PieceColor = color === "white" ? "black" : "white";
const castling = getCastlingMoves(
this.session,
piece.id,
(s, sq) => isSquareAttacked(s, sq, enemyColor),
);
pieceMoves = [...pieceMoves, ...castling];
}
// Replace raw promotion-rank pawn moves with promotion-tagged variants
if (piece.type === "pawn") {
const promotions = getPromotionMoves(this.session, piece.id);
if (promotions.length > 0) {
const promotionTos = new Set(promotions.map(m => m.to));
pieceMoves = pieceMoves.filter(m => !promotionTos.has(m.to));
pieceMoves = [...pieceMoves, ...promotions];
}
}
moves.push(...pieceMoves);
}
// Filter self-check moves
return filterSelfCheckMoves(this.session, moves, color);
}
applyMove(move: LegalMove, promoteTo: PieceType = "queen"): GameResult {
const color = this.getCurrentTurn();
const facts = this.session.allFacts();
const movingType = facts.find(
f => f.id === move.pieceId && f.attr === "PieceType",
)?.value as PieceType;
const epTarget = this.session.get(GAME_ENTITY, "EnPassantTarget");
const isEnPassant =
movingType === "pawn" &&
epTarget !== null &&
epTarget !== undefined &&
epTarget === move.to;
const isCastling = (move as CastlingMove).isCastling === true;
if (isEnPassant) {
applyEnPassantCapture(this.session, move, color);
} else if (isCastling) {
applyCastlingMove(this.session, move as CastlingMove);
} else {
// Normal move: handle capture, then update position
if (move.isCapture) {
const capturedId = this.getPieceAt(move.to);
if (capturedId !== null) {
applyCapture(this.session, capturedId);
}
}
this.session.insert(move.pieceId, "Position", move.to);
this.session.insert(move.pieceId, "HasMoved", true);
}
// Handle promotion (pawn reaching last rank)
const effectiveTo = isCastling ? (move as CastlingMove).to : move.to;
if (movingType === "pawn" && isPromotionMove(effectiveTo, color)) {
const promoteAs =
(move as LegalMove & { promoteTo?: PieceType }).promoteTo ?? promoteTo;
applyPromotion(this.session, move.pieceId, promoteAs);
}
// Set/clear en passant target
if (movingType === "pawn" && Math.abs(move.to - move.from) === 16) {
setEnPassantTarget(this.session, move.from, move.to);
} else {
clearEnPassantTarget(this.session);
}
// Update halfmove clock
updateHalfmoveClock(this.session, move, movingType === "pawn");
// Switch turn
const nextColor: PieceColor = color === "white" ? "black" : "white";
this.session.insert(GAME_ENTITY, "Turn", nextColor);
// Increment fullmove number after black's move
if (color === "black") {
const fn =
((this.session.get(GAME_ENTITY, "FullmoveNumber") as number) ?? 1) + 1;
this.session.insert(GAME_ENTITY, "FullmoveNumber", fn);
}
// Record position for threefold repetition
recordPosition(this.session);
return this.checkGameResult();
}
checkGameResult(): GameResult {
const nextColor = this.getCurrentTurn();
if (isCheckmate(this.session, nextColor)) return "checkmate";
if (isStalemate(this.session, nextColor)) return "stalemate";
if (isFiftyMoveDraw(this.session)) return "draw-50";
if (isThreefoldRepetition(this.session)) return "draw-3fold";
if (isInsufficientMaterial(this.session)) return "draw-insufficient";
return "ongoing";
}
/** Find first legal move matching from+to squares and optional promoteTo. */
findMove(from: number, to: number, promoteTo?: PieceType): LegalMove | null {
return (
this.getAllLegalMoves().find(
m =>
m.from === from &&
m.to === to &&
(!m.promoteTo || m.promoteTo === (promoteTo ?? "queen")),
) ?? null
);
}
private getPieceAt(square: number): EntityId | null {
const f = this.session
.allFacts()
.find(x => x.attr === "Position" && x.value === square && (x.id as number) > 0);
return f ? (f.id as EntityId) : null;
}
}

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packages/chess/src/pgn.ts Normal file
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/**
* Minimal PGN/SAN parser for @paratype/chess.
* Parses standard algebraic notation moves no external dependencies.
*/
import { algebraicToSquare } from "./coord.js";
import type { PieceType } from "./schema.js";
export interface ParsedMove {
/** Full from-square when fully disambiguated (e.g. "Nb3d5"). */
from?: number;
/** File hint (0-7) when only file is given (e.g. "exd5" → fromFile=4). */
fromFile?: number;
/** Rank hint (0-7) when only rank is given (e.g. "N3d5" → fromRank=2). */
fromRank?: number;
/** Target square. -1 for castling (use isCastlingKingside/Queenside). */
to: number;
pieceType: PieceType;
isCapture: boolean;
promoteTo?: PieceType;
isCastlingKingside?: boolean;
isCastlingQueenside?: boolean;
}
const PIECE_MAP: Record<string, PieceType> = {
N: "knight",
B: "bishop",
R: "rook",
Q: "queen",
K: "king",
};
/**
* Parse a SAN move string into a ParsedMove.
* Handles: e4, Nf3, exd5, Nbd7, N3d5, Nb3d5, O-O, O-O-O, e8=Q, exd8=R, etc.
* Strips trailing +, #, !, ? annotation characters.
*/
export function parseSanMove(san: string): ParsedMove {
// Strip check/checkmate/annotation indicators
const clean = san.replace(/[+#!?]+$/g, "");
// ── Castling ──────────────────────────────────────────────────────────────
if (clean === "O-O" || clean === "0-0") {
return {
to: -1,
pieceType: "king",
isCapture: false,
isCastlingKingside: true,
};
}
if (clean === "O-O-O" || clean === "0-0-0") {
return {
to: -1,
pieceType: "king",
isCapture: false,
isCastlingQueenside: true,
};
}
let remaining = clean;
// ── Promotion: trailing =Q or Q ──────────────────────────────────────────
let promoteTo: PieceType | undefined;
const promoMatch = remaining.match(/=?([NBRQ])$/);
if (promoMatch && !PIECE_MAP[remaining[0]!]) {
// Only treat it as promotion when the first character is NOT a piece letter
// (i.e., this is a pawn move, not e.g. "Qe8" where 'Q' is the piece type)
const promoPiece = PIECE_MAP[promoMatch[1]!];
if (promoPiece) {
promoteTo = promoPiece;
remaining = remaining.slice(0, promoMatch.index);
}
}
// ── Piece type ────────────────────────────────────────────────────────────
let pieceType: PieceType = "pawn";
if (PIECE_MAP[remaining[0]!]) {
pieceType = PIECE_MAP[remaining[0]!]!;
remaining = remaining.slice(1);
}
// ── Capture indicator ─────────────────────────────────────────────────────
const isCapture = remaining.includes("x");
remaining = remaining.replace("x", "");
// ── Target square (always last 2 chars) ───────────────────────────────────
if (remaining.length < 2) {
throw new Error(`Cannot parse SAN: "${san}"`);
}
const toNotation = remaining.slice(-2);
const to = algebraicToSquare(toNotation);
if (to < 0) {
throw new Error(`Invalid target square "${toNotation}" in SAN: "${san}"`);
}
// ── Disambiguation prefix ─────────────────────────────────────────────────
const disambiguation = remaining.slice(0, -2);
let from: number | undefined;
let fromFile: number | undefined;
let fromRank: number | undefined;
if (disambiguation.length === 2) {
// Full from-square disambiguation: e.g. "b3" in "Nb3d5"
const sq = algebraicToSquare(disambiguation);
if (sq >= 0) from = sq;
} else if (disambiguation.length === 1) {
const ch = disambiguation[0]!;
if (ch >= "a" && ch <= "h") {
fromFile = ch.charCodeAt(0) - 97; // 'a'=0
} else if (ch >= "1" && ch <= "8") {
fromRank = parseInt(ch, 10) - 1; // rank 1 → 0
}
}
return {
to,
pieceType,
isCapture,
...(from !== undefined && { from }),
...(fromFile !== undefined && { fromFile }),
...(fromRank !== undefined && { fromRank }),
...(promoteTo !== undefined && { promoteTo }),
};
}
/**
* Extract SAN move tokens from a PGN string.
* Strips move numbers, comments, variations, and result strings.
*/
export function extractMoves(pgn: string): string[] {
return pgn
.replace(/\{[^}]*\}/g, "") // remove { comments }
.replace(/\([^)]*\)/g, "") // remove (variations)
.replace(/\d+\.\.\./g, "") // remove "1..." black move numbers
.replace(/\d+\./g, "") // remove "1." move numbers
.replace(/1-0|0-1|1\/2-1\/2|\*/g, "") // remove result tokens
.split(/\s+/)
.map(s => s.trim())
.filter(s => s.length > 0 && !/^\d+$/.test(s));
}

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/**
* FIDE game replay integration tests (P2.23).
*
* Each test replays a real chess game (or opening sequence) through the
* rules engine, asserting that every move is accepted without error and
* that the correct terminal state is detected.
*/
import { describe, it, expect } from "vitest";
import { ChessEngine, type GameResult } from "../../src/engine.js";
import { parseSanMove } from "../../src/pgn.js";
import type { LegalMove } from "../../src/rules/types.js";
import type { CastlingMove } from "../../src/rules/castling.js";
// ── Move resolution ─────────────────────────────────────────────────────────
/**
* Resolve a SAN string against the engine's current legal moves.
* Uses piece-type, target square, and available disambiguation fields
* (full from-square, file hint, rank hint) to identify the unique legal move.
*/
function resolveMove(engine: ChessEngine, san: string): LegalMove {
const parsed = parseSanMove(san);
const legalMoves = engine.getAllLegalMoves();
// ── Castling ──
if (parsed.isCastlingKingside || parsed.isCastlingQueenside) {
const m = legalMoves.find(
mv =>
(mv as CastlingMove).isCastling === true &&
((parsed.isCastlingKingside && (mv as CastlingMove).side === "kingside") ||
(parsed.isCastlingQueenside && (mv as CastlingMove).side === "queenside")),
);
if (!m) {
throw new Error(
`Castling not available for "${san}" (turn=${engine.getCurrentTurn()})`,
);
}
return m;
}
// ── Piece/pawn moves ──
const facts = engine.session.allFacts();
const candidates = legalMoves.filter(mv => {
// Filter by target square
if (mv.to !== parsed.to) return false;
// Filter by piece type
const typeFact = facts.find(
f => f.id === mv.pieceId && f.attr === "PieceType",
);
if (typeFact?.value !== parsed.pieceType) return false;
// Disambiguation: full from-square
if (parsed.from !== undefined && mv.from !== parsed.from) return false;
// Disambiguation: file hint
if (parsed.fromFile !== undefined && (mv.from % 8) !== parsed.fromFile) {
return false;
}
// Disambiguation: rank hint
if (
parsed.fromRank !== undefined &&
Math.floor(mv.from / 8) !== parsed.fromRank
) {
return false;
}
return true;
});
if (candidates.length === 0) {
const turn = engine.getCurrentTurn();
const allMovesSummary = legalMoves
.slice(0, 8)
.map(mv => `${mv.from}${mv.to}`)
.join(", ");
throw new Error(
`No legal move found for "${san}" ` +
`(to=${parsed.to}, type=${parsed.pieceType}, turn=${turn}). ` +
`First 8 legal moves: ${allMovesSummary}`,
);
}
// If promotion, prefer the matching promoteTo variant
if (parsed.promoteTo) {
const promo = candidates.find(mv => mv.promoteTo === parsed.promoteTo);
if (promo) return promo;
}
return candidates[0]!;
}
/**
* Play a sequence of SAN moves on a fresh engine.
* Returns the engine and the result string after the last move.
*/
function playGame(moves: string[]): { engine: ChessEngine; result: GameResult } {
const engine = new ChessEngine();
let result: GameResult = "ongoing";
for (const san of moves) {
const move = resolveMove(engine, san);
result = engine.applyMove(move, move.promoteTo ?? "queen");
}
return { engine, result };
}
// ── Tests ───────────────────────────────────────────────────────────────────
describe("Classic chess games — FIDE replay (P2.23)", () => {
// ── 1. Fool's Mate ────────────────────────────────────────────────────────
// Shortest possible checkmate: white self-destructs in 2 moves.
it("Fool's Mate (2 white moves, white checkmated)", () => {
// 1. f3 e5 2. g4 Qh4#
const { result } = playGame(["f3", "e5", "g4", "Qh4"]);
expect(result).toBe("checkmate");
});
// ── 2. Scholar's Mate ─────────────────────────────────────────────────────
// Classic 4-move checkmate against a careless black.
it("Scholar's Mate (4 moves, black checkmated)", () => {
// 1. e4 e5 2. Bc4 Nc6 3. Qh5 Nf6?? 4. Qxf7#
const { result } = playGame(["e4", "e5", "Bc4", "Nc6", "Qh5", "Nf6", "Qxf7"]);
expect(result).toBe("checkmate");
});
// ── 3. Ruy López opening (6 moves) ───────────────────────────────────────
it("Ruy López opening plays 6 moves without error", () => {
// 1. e4 e5 2. Nf3 Nc6 3. Bb5 a6
const { engine, result } = playGame(["e4", "e5", "Nf3", "Nc6", "Bb5", "a6"]);
expect(result).toBe("ongoing");
// After 6 half-moves (3 full), white to move
expect(engine.getCurrentTurn()).toBe("white");
});
// ── 4. Sicilian Defense — capture on d4 ───────────────────────────────────
it("Sicilian Defense — pawn capture cxd4 on move 3", () => {
// 1. e4 c5 2. Nf3 d6 3. d4 cxd4
const { engine, result } = playGame(["e4", "c5", "Nf3", "d6", "d4", "cxd4"]);
expect(result).toBe("ongoing");
// 6 half-moves played; white to move
expect(engine.getCurrentTurn()).toBe("white");
});
// ── 5. Italian Game — 10 moves with bishop capture ───────────────────────
it("Italian Game / Evans Gambit opening — 10 moves, bishop capture", () => {
// 1. e4 e5 2. Nf3 Nc6 3. Bc4 Bc5 4. b4 Bxb4 5. c3 Ba5
const moves = ["e4", "e5", "Nf3", "Nc6", "Bc4", "Bc5", "b4", "Bxb4", "c3", "Ba5"];
const { engine, result } = playGame(moves);
expect(result).toBe("ongoing");
// 10 half-moves (5 full), white to move
expect(engine.getCurrentTurn()).toBe("white");
});
});