/*
 * 五子棋规则引擎（纯逻辑，无 DOM）
 * 浏览器中挂到 window.GomokuEngine，Node 中通过 module.exports 导出供测试使用。
 * 规则：无禁手自由规则，任意方向连成五子及以上即胜。
 */
(function (root, factory) {
  const api = factory();
  if (typeof module !== 'undefined' && module.exports) {
    module.exports = api;
  } else {
    root.GomokuEngine = api;
  }
})(typeof window !== 'undefined' ? window : globalThis, function () {

  const SIZE = 15;
  const EMPTY = 0;
  const BLACK = 1;
  const WHITE = 2;

  // 横、竖、两条斜线
  const DIRECTIONS = [[1, 0], [0, 1], [1, 1], [1, -1]];

  function inBounds(x, y) {
    return x >= 0 && x < SIZE && y >= 0 && y < SIZE;
  }

  function createGame() {
    return {
      size: SIZE,
      board: Array.from({ length: SIZE }, () => new Array(SIZE).fill(EMPTY)),
      currentPlayer: BLACK, // 黑先
      winner: 0,            // 1 黑胜，2 白胜，0 未分
      draw: false,
      gameOver: false,
      winningLine: null,    // 获胜连线的坐标数组 [{x, y}, ...]
      moveHistory: [],      // {x, y, player}，为悔棋功能预留
    };
  }

  // 从 (x, y) 出发沿 4 个方向数连子，返回获胜连线（≥5 个）或 null
  function checkWinAt(game, x, y) {
    const player = game.board[y][x];
    if (player === EMPTY) return null;
    for (const [dx, dy] of DIRECTIONS) {
      const line = [{ x, y }];
      for (let nx = x + dx, ny = y + dy; inBounds(nx, ny) && game.board[ny][nx] === player; nx += dx, ny += dy) {
        line.push({ x: nx, y: ny });
      }
      for (let nx = x - dx, ny = y - dy; inBounds(nx, ny) && game.board[ny][nx] === player; nx -= dx, ny -= dy) {
        line.unshift({ x: nx, y: ny });
      }
      if (line.length >= 5) return line;
    }
    return null;
  }

  function isBoardFull(game) {
    return game.board.every(row => row.every(c => c !== EMPTY));
  }

  function place(game, x, y) {
    if (game.gameOver) return { ok: false, reason: '游戏已结束' };
    if (!inBounds(x, y)) return { ok: false, reason: '超出棋盘范围' };
    if (game.board[y][x] !== EMPTY) return { ok: false, reason: '该位置已有棋子' };

    game.board[y][x] = game.currentPlayer;
    game.moveHistory.push({ x, y, player: game.currentPlayer });

    const line = checkWinAt(game, x, y);
    if (line) {
      game.winner = game.currentPlayer;
      game.winningLine = line;
      game.gameOver = true;
      return { ok: true, win: true };
    }
    if (isBoardFull(game)) {
      game.draw = true;
      game.gameOver = true;
      return { ok: true, draw: true };
    }
    game.currentPlayer = game.currentPlayer === BLACK ? WHITE : BLACK;
    return { ok: true };
  }

  return {
    SIZE,
    EMPTY,
    BLACK,
    WHITE,
    createGame,
    place,
    checkWinAt,
    inBounds,
  };
});