houserules/packages/chess/tests/fide-games/classic-games.test.ts

/**
 * 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");
  });
});