feat(bot): CasualBrain with capture/development/center heuristics

2026-04-28 13:48:34 -04:00
parent f48e0a9cdf
commit aa7bc30ee1
2 changed files with 282 additions and 0 deletions
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+import { describe, it, expect } from 'vitest';
+import { CasualBrain } from '../../../src/bot/casual-brain.js';
+import type { BrainInput, CandidateMove } from '../../../src/bot/brain.js';
+import type { BoardView } from '@blind-chess/shared';
+
+function makeInput(overrides: Partial<BrainInput> = {}): BrainInput {
+  const view: BoardView = {
+    pieces: { e2: { color: 'w', type: 'p' } },
+    toMove: 'w',
+    inCheck: false,
+  };
+  return {
+    view,
+    newAnnouncements: [],
+    legalCandidates: [{ from: 'e2', to: 'e4' }],
+    attemptHistory: [],
+    drawOfferFromOpponent: false,
+    ply: 0,
+    ...overrides,
+  };
+}
+
+describe('CasualBrain', () => {
+  it('init() resolves', async () => {
+    const brain = new CasualBrain({ seed: 1 });
+    await brain.init({ color: 'w', mode: 'blind', gameId: 'casualab' });
+  });
+
+  it('single candidate -> picks it', async () => {
+    const brain = new CasualBrain({ seed: 1 });
+    await brain.init({ color: 'w', mode: 'blind', gameId: 'g1' });
+    const action = await brain.decide(makeInput());
+    expect(action.type).toBe('commit');
+    if (action.type === 'commit') {
+      expect(action.from).toBe('e2');
+      expect(action.to).toBe('e4');
+    }
+  });
+
+  it('zero candidates -> throws', async () => {
+    const brain = new CasualBrain({ seed: 1 });
+    await brain.init({ color: 'w', mode: 'blind', gameId: 'g1' });
+    await expect(brain.decide(makeInput({ legalCandidates: [] }))).rejects.toThrow();
+  });
+
+  it('attemptHistory excludes the rejected move', async () => {
+    const brain = new CasualBrain({ seed: 1 });
+    await brain.init({ color: 'w', mode: 'blind', gameId: 'g1' });
+    const input = makeInput({
+      legalCandidates: [
+        { from: 'e2', to: 'e4' },
+        { from: 'd2', to: 'd4' },
+      ],
+      attemptHistory: [{ move: { from: 'e2', to: 'e4' }, rejection: 'wont_help' }],
+    });
+    const action = await brain.decide(input);
+    expect(action.type).toBe('commit');
+    if (action.type === 'commit') {
+      expect(action.from).toBe('d2');
+      expect(action.to).toBe('d4');
+    }
+  });
+
+  it('promotion: when multiple candidates differ only by promotion, picks queen', async () => {
+    const brain = new CasualBrain({ seed: 1 });
+    await brain.init({ color: 'w', mode: 'blind', gameId: 'g1' });
+    const candidates: CandidateMove[] = [
+      { from: 'a7', to: 'a8', promotion: 'q' },
+      { from: 'a7', to: 'a8', promotion: 'r' },
+      { from: 'a7', to: 'a8', promotion: 'b' },
+      { from: 'a7', to: 'a8', promotion: 'n' },
+    ];
+    const action = await brain.decide(makeInput({ legalCandidates: candidates }));
+    if (action.type === 'commit') expect(action.promotion).toBe('q');
+  });
+
+  it('draw offer at material parity -> accept', async () => {
+    const brain = new CasualBrain({ seed: 1 });
+    await brain.init({ color: 'w', mode: 'blind', gameId: 'g1' });
+    // White has 1 king + 1 rook = 5 material; Casual heuristic accepts when own material < 15.
+    const view: BoardView = {
+      pieces: {
+        e1: { color: 'w', type: 'k' },
+        a1: { color: 'w', type: 'r' },
+      },
+      toMove: 'w', inCheck: false,
+    };
+    const action = await brain.decide({
+      view, newAnnouncements: [], legalCandidates: [{ from: 'e1', to: 'e2' }],
+      attemptHistory: [], drawOfferFromOpponent: true, ply: 30,
+    });
+    expect(action.type).toBe('respond-draw');
+    if (action.type === 'respond-draw') expect(action.accept).toBe(true);
+  });
+
+  it('never voluntarily offers resign', async () => {
+    const brain = new CasualBrain({ seed: 1 });
+    await brain.init({ color: 'w', mode: 'blind', gameId: 'g1' });
+    for (let i = 0; i < 50; i++) {
+      const action = await brain.decide(makeInput({ ply: i }));
+      expect(action.type).not.toBe('resign');
+    }
+  });
+
+  it('seeded determinism: same seed + same input -> same move', async () => {
+    const candidates: CandidateMove[] = [
+      { from: 'e2', to: 'e4' },
+      { from: 'd2', to: 'd4' },
+      { from: 'g1', to: 'f3' },
+    ];
+    const a = new CasualBrain({ seed: 42 });
+    await a.init({ color: 'w', mode: 'blind', gameId: 'g1' });
+    const b = new CasualBrain({ seed: 42 });
+    await b.init({ color: 'w', mode: 'blind', gameId: 'g1' });
+    const aAct = await a.decide(makeInput({ legalCandidates: candidates }));
+    const bAct = await b.decide(makeInput({ legalCandidates: candidates }));
+    expect(aAct).toEqual(bAct);
+  });
+
+  it('opening moves favor center pawns over flank pawns (e/d > a/h)', async () => {
+    const candidates: CandidateMove[] = [
+      { from: 'a2', to: 'a3' },
+      { from: 'h2', to: 'h3' },
+      { from: 'e2', to: 'e4' },
+      { from: 'd2', to: 'd4' },
+    ];
+    // Many seeds → assert e2 or d2 wins majority. The score gap (center pawn
+    // scores ~25 + 15*2 = 55 over flank pawn ~15*1 = 15) is well over the
+    // 0.01 random tiebreak, so center should win nearly always.
+    let centerHits = 0;
+    for (let s = 0; s < 20; s++) {
+      const b = new CasualBrain({ seed: s });
+      await b.init({ color: 'w', mode: 'blind', gameId: 'g1' });
+      const a = await b.decide(makeInput({ legalCandidates: candidates, ply: 0 }));
+      if (a.type === 'commit' && (a.from === 'e2' || a.from === 'd2')) centerHits++;
+    }
+    expect(centerHits).toBeGreaterThan(15);
+  });
+});