export const is_empty = 'isEmpty';
/**
 * 机器人
 */
export const is_white = 'isWhite';
export const is_black = 'isBlack';
export const directions = [
  [1, 0],        // 水平方向
  [0, 1],        // 垂直方向
  [1, 1],        // 右下方向
  [1, -1]        // 左下方向
]

/**
 * 检查四个方向连续的棋子数
 * @param {object} param 
 * @param {number} param.row 行
 * @param {number} param.col 列
 * @param {(is_empty|is_white|is_black)[]} param.board 棋盘
 * @param {is_white|is_black} [param.player] 当前棋子类型
 * @param {number} param.win_size 需要几个棋子才赢
 * @param {[][]} [param.direction] 方向
 * @returns 
 */
export function checkWin({ row, col, board, player, win_size, direction }) {
  const _row = board.length;
  const _col = board[0].length
  const pieceType = player ?? board[row][col]
  let res = []


  const _directions = direction ? [direction] : directions;

  for (let i = 0; i < _directions.length; i++) {
    res = [[row, col]];
    const [dx, dy] = _directions[i];
    let x = row + dx;
    let y = col + dy;

    // 向正反两个方向扩展，检查是否有连续的五个相同棋子
    while (x >= 0 && x < _row && y >= 0 && y < _col && board[x][y] === pieceType) {
      res.push([x, y])
      x += dx;
      y += dy;
    }

    x = row - dx;
    y = col - dy;
    while (x >= 0 && x < _row && y >= 0 && y < _col && board[x][y] === pieceType) {
      res.push([x, y])
      x -= dx;
      y -= dy;
    }

    // 出现五连珠，返回胜利
    if (res.length >= win_size) {
      return res;
    }
  }
  // 当前空位，可以结成多少颗连珠
  return res;
}

/**
 * 机器人下棋位置
 * @param {(is_empty|is_white|is_black)[][]} board 棋盘
 * @param {is_white} robot 机器人
 * @param {number} win_size 赢棋的棋子颗数
 * @returns {number[]} 
 */
export function robotPlay(board, robot, win_size) {
  // 深度复制一份棋盘 
  const _board = JSON.parse(JSON.stringify(board))
  const maxScorePos = {};
  let maxScore = -1;
  // 空位
  const empty_points = _board.map((item, row) => {
    return item.flatMap((_item, col) => _item === is_empty ? [[row, col]] : [])
  }).flat(1)

  // 对每个空位进行评分
  for (let e_i = 0; e_i < empty_points.length; e_i++) {
    const point = empty_points[e_i]

    let score = 0;
    const [i, j] = point;

    // 判断下子后是否获胜
    _board[i][j] = is_white;
    const win = checkWin({ row: i, col: j, board: _board, player: robot, win_size });
    if (win.length >= win_size) {
      return [i, j]
    } else {
      // 判断对手是否能在下一步获胜
      const oppWin = checkWin({ row: i, col: j, board: _board, player: is_black, win_size });
      if (oppWin.length >= win_size) {
        return [i, j]
      } else {
        // 计算当前棋盘局面的得分
        const horizontal = checkWin({ row: i, col: j, board: _board, player: is_black, win_size, direction: getDirection("horizontal") });
        const vertical = checkWin({ row: i, col: j, board: _board, player: is_black, win_size, direction: getDirection("vertical") });
        const diagonalDown = checkWin({ row: i, col: j, board: _board, player: is_black, win_size, direction: getDirection("diagonalDown") });
        const diagonalUp = checkWin({ row: i, col: j, board: _board, player: is_black, win_size, direction: getDirection("diagonalUp") });

        score = Math.max(horizontal.length, vertical.length, diagonalDown.length, diagonalUp.length);
      }
    }

    _board[i][j] = is_empty; // 恢复棋盘状态

    // 选取分数最高的空位
    if (score > maxScore) {
      maxScorePos.x = i;
      maxScorePos.y = j;
      maxScore = score;
    }
  };

  return [maxScorePos.x, maxScorePos.y];
}

// 获取某个方向的偏移量
function getDirection(direction) {
  switch (direction) {
    case "horizontal":
      return [0, 1];
    case "vertical":
      return [1, 0];
    case "diagonalDown":
      return [1, 1];
    case "diagonalUp":
      return [1, -1];
    default:
      return [0, 0];
  }
}