import { describe, it, expect } from 'vitest';
import { DuplicateGame } from './game';
import { playSymmetric } from './test-helpers';
import { ghosts } from './ghosts';

describe('ghosts', () => {
  it('reports no ghosts at the start', () => {
    expect(ghosts(new DuplicateGame())).toEqual([]);
  });

  it('forms a ghost when a piece is captured on one board but not its twin', () => {
    const g = new DuplicateGame();
    // Symmetric opening so all four boards stay identical...
    playSymmetric(g, [
      [{ from: 'e2', to: 'e4' }, { from: 'e7', to: 'e5' }],
      [{ from: 'g1', to: 'f3' }, { from: 'b8', to: 'c6' }],
    ]);
    // ...then North & South each play Nxe5 (capturing the e5 pawn),
    // and East captures that knight only on its boards (NE, SE).
    g.applyMove({ from: 'f3', to: 'e5' }); // N: Nf3xe5 on NW, NE
    g.applyMove({ from: 'f3', to: 'e5' }); // S: Nf3xe5 on SW, SE
    g.applyMove({ from: 'c6', to: 'e5' }); // E: Nc6xe5 on NE, SE — captures the white knight
    // North's knight on e5 survives on NW but was captured on NE -> NW/e5 is a ghost.
    // South's knight on e5 survives on SW but was captured on SE -> SW/e5 is a ghost.
    const result = ghosts(g).sort((x, y) => (x.board < y.board ? -1 : 1));
    expect(result).toEqual([
      { board: 'NW', square: 'e5' },
      { board: 'SW', square: 'e5' },
    ]);
  });
});