const { POWER_CALC } = require('../config/constants');

/**
 * 战力值计算服务
 */
class PowerCalculator {
  /**
   * 计算单场比赛战力值变动
   * @param {Object} winner - 胜者信息 { powerScore, level, protectedMatches }
   * @param {Object} loser - 败者信息 { powerScore, level, protectedMatches }
   * @param {number} matchWeight - 比赛权重
   * @returns {Object} { winnerChange, loserChange }
   */
  static calculate(winner, loser, matchWeight = 1.0) {
    const { BASE_WIN, BASE_LOSE, UNDERDOG_THRESHOLD, UNDERDOG_RATE, MAX_CHANGE, NEWBIE_PROTECTION, NEWBIE_LOSE_RATE } = POWER_CALC;

    // 计算分差
    const diff = loser.powerScore - winner.powerScore;

    // 基础得分
    let winnerChange = BASE_WIN;
    let loserChange = BASE_LOSE;

    // 以下克上奖励
    if (diff >= UNDERDOG_THRESHOLD) {
      const bonus = Math.ceil(diff * UNDERDOG_RATE);
      winnerChange += bonus;
    }

    // 应用比赛权重
    winnerChange = Math.round(winnerChange * matchWeight);
    loserChange = Math.round(loserChange * matchWeight);

    // 新手保护（Lv1和Lv2，前5场）
    if (loser.level <= 2 && loser.protectedMatches < NEWBIE_PROTECTION) {
      loserChange = Math.round(loserChange * NEWBIE_LOSE_RATE);
    }

    // 封顶限制
    winnerChange = Math.min(winnerChange, MAX_CHANGE);
    loserChange = Math.max(loserChange, -MAX_CHANGE);

    return {
      winnerChange,
      loserChange
    };
  }

  /**
   * 检查挑战赛冷却期
   * @param {Date} lastMatchTime - 上次比赛时间
   * @returns {boolean} 是否可以挑战
   */
  static canChallenge(lastMatchTime) {
    if (!lastMatchTime) return true;

    const cooldownDays = POWER_CALC.CHALLENGE_COOLDOWN;
    const cooldownMs = cooldownDays * 24 * 60 * 60 * 1000;
    const timeDiff = Date.now() - new Date(lastMatchTime).getTime();

    return timeDiff >= cooldownMs;
  }

  /**
   * 获取冷却剩余天数
   * @param {Date} lastMatchTime - 上次比赛时间
   * @returns {number} 剩余天数
   */
  static getCooldownDays(lastMatchTime) {
    if (!lastMatchTime) return 0;

    const cooldownDays = POWER_CALC.CHALLENGE_COOLDOWN;
    const cooldownMs = cooldownDays * 24 * 60 * 60 * 1000;
    const timeDiff = Date.now() - new Date(lastMatchTime).getTime();

    if (timeDiff >= cooldownMs) return 0;

    return Math.ceil((cooldownMs - timeDiff) / (24 * 60 * 60 * 1000));
  }

  /**
   * 判断升降级（排位赛结束后）
   * 规则：
   * - 只有冠军晋级（+1 段位，最高不超过 5 段）
   * - 只有最后一名且当前段位为 4 或 5 时降级（-1 段位）
   * @param {number} rank - 排名 (1-based)
   * @param {number} totalPlayers - 总人数
   * @returns {string} 'promote' | 'demote' | 'stay'
   */
  static determinePromotion(rank, totalPlayers) {
    if (rank === 1) {
      return 'promote'; // 仅冠军晋级
    }
    if (rank === totalPlayers) {
      return 'demote'; // 仅最后一名有降级资格（具体是否降，看段位）
    }
    return 'stay'; // 其它名次保持不变
  }

  /**
   * 计算消费积分
   * @param {number} amount - 消费金额
   * @returns {number} 积分
   */
  static calculateConsumePoints(amount) {
    return Math.floor(amount / 10);
  }
}

module.exports = PowerCalculator;