feat(engine): DuplicateGame core — boards, history, undo, draw clocks

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/engine/game.test.ts

@@ -0,0 +1,73 @@
+import { describe, it, expect } from 'vitest';
+import { DuplicateGame } from './game';
+
+const START = 'rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR';
+
+function placement(fen: string) {
+  return fen.split(' ')[0];
+}
+
+describe('DuplicateGame', () => {
+  it('starts with four boards in the standard position, North to move', () => {
+    const g = new DuplicateGame();
+    expect(g.ply).toBe(0);
+    expect(g.currentPlayer).toBe('N');
+    for (const id of ['NW', 'NE', 'SW', 'SE'] as const) {
+      expect(placement(g.boards[id].fen())).toBe(START);
+    }
+  });
+
+  it("applies a synchronized move to the current player's two boards only", () => {
+    const g = new DuplicateGame();
+    g.applyMove({ from: 'e2', to: 'e4' }); // North
+    expect(g.ply).toBe(1);
+    expect(g.currentPlayer).toBe('S');
+    expect(placement(g.boards.NW.fen())).toContain('4P3'); // pawn advanced
+    expect(placement(g.boards.NE.fen())).toContain('4P3');
+    expect(placement(g.boards.SW.fen())).toBe(START); // untouched
+    expect(placement(g.boards.SE.fen())).toBe(START);
+  });
+
+  it('cycles the current player N -> S -> E -> W -> N', () => {
+    const g = new DuplicateGame();
+    g.applyMove({ from: 'e2', to: 'e4' }); // N
+    g.applyMove({ from: 'e2', to: 'e4' }); // S
+    g.applyMove({ from: 'e7', to: 'e5' }); // E
+    g.applyMove({ from: 'e7', to: 'e5' }); // W
+    expect(g.currentPlayer).toBe('N');
+    expect(g.ply).toBe(4);
+  });
+
+  it("throws on a move not legal on both of the player's boards", () => {
+    const g = new DuplicateGame();
+    expect(() => g.applyMove({ from: 'e2', to: 'e5' })).toThrow();
+  });
+
+  it('undo removes the last move and restores the position', () => {
+    const g = new DuplicateGame();
+    g.applyMove({ from: 'e2', to: 'e4' });
+    g.undo();
+    expect(g.ply).toBe(0);
+    expect(g.currentPlayer).toBe('N');
+    expect(placement(g.boards.NW.fen())).toBe(START);
+  });
+
+  it('rebuilds from a history array passed to the constructor', () => {
+    const g = new DuplicateGame([
+      { player: 'N', from: 'e2', to: 'e4' },
+      { player: 'S', from: 'e2', to: 'e4' },
+    ]);
+    expect(g.ply).toBe(2);
+    expect(g.currentPlayer).toBe('E');
+  });
+
+  it('resets the progress clock on a pawn move or capture', () => {
+    const g = new DuplicateGame();
+    g.applyMove({ from: 'e2', to: 'e4' }); // pawn move -> clock stays 0
+    expect(g.pliesSinceProgress).toBe(0);
+    g.applyMove({ from: 'e2', to: 'e4' }); // pawn move
+    expect(g.pliesSinceProgress).toBe(0);
+    g.applyMove({ from: 'g8', to: 'f6' }); // knight move -> clock increments
+    expect(g.pliesSinceProgress).toBe(1);
+  });
+});