import { Lunar } from 'lunar-javascript';

export interface CountdownResult {
  days: number;
  hours: number;
  minutes: number;
  seconds: number;
  nextDate: Date;
  isToday: boolean;
  isPast: boolean;
}

/**
 * 安全地创建日期，处理月末边界情况
 * 某些月份只有28/29/30/31天
 */
function safeCreateDate(year: number, month: number, day: number): Date {
  const date = new Date(year, month, day);
  // 如果日期溢出（如下个月），自动调整到月末
  if (date.getMonth() !== month % 12) {
    date.setMonth(month + 1, 0);
  }
  return date;
}

/**
 * 安全地创建农历日期，处理月末边界情况
 * 某些农历月份只有29或30天，需要检查并调整
 */
function safeCreateLunarDate(year: number, month: number, day: number): { lunar: Lunar; solar: Solar } | null {
  try {
    const lunar = Lunar.fromYmd(year, month, day);
    return { lunar, solar: lunar.getSolar() };
  } catch {
    // 如果日期不存在（如农历12月30日在只有29天的月份），
    // 尝试获取该月的最后一天
    try {
      // 获取下个月的农历日期，然后往前推一天
      const nextMonthLunar = Lunar.fromYmd(year, month + 1, 1);
      const lastDayOfMonth = nextMonthLunar.getLunar().getDay() - 1;
      if (lastDayOfMonth > 0) {
        const lunar = Lunar.fromYmd(year, month, lastDayOfMonth);
        return { lunar, solar: lunar.getSolar() };
      }
    } catch {
      // 仍然失败，返回null
    }
    return null;
  }
}

/**
 * 计算纪念日的倒计时
 * 考虑重复规则，计算下一个 occurrence 的倒计时
 */
export function calculateCountdown(
  dateStr: string,
  repeatType: 'yearly' | 'monthly' | 'daily' | 'weekly' | 'none',
  isLunar: boolean
): CountdownResult {
  const now = new Date();
  const today = new Date(now.getFullYear(), now.getMonth(), now.getDate());
  let targetDate: Date;
  let isPast = false;

  // 解析日期字符串
  // 格式假设为 ISO 格式 "YYYY-MM-DD" 或完整的 ISO datetime
  const dateParts = dateStr.split('T')[0].split('-').map(Number);
  const originalYear = dateParts[0];
  const originalMonth = dateParts[1] - 1; // JavaScript月份从0开始
  const originalDay = dateParts[2];

  // 获取原始时间（小时和分钟）
  const timeParts = dateStr.includes('T') ? dateStr.split('T')[1].split(':') : ['00', '00'];
  const originalHours = parseInt(timeParts[0]) || 0;
  const originalMinutes = parseInt(timeParts[1]) || 0;

  // 保存农历月份和日期（用于年度重复计算）
  let lunarMonth: number | null = null;
  let lunarDay: number | null = null;

  if (isLunar) {
    // 农历日期：使用安全方法创建，处理月末边界
    const result = safeCreateLunarDate(originalYear, originalMonth + 1, originalDay);
    if (result) {
      // 保存农历日期
      lunarMonth = result.lunar.getMonth();
      lunarDay = result.lunar.getDay();
      targetDate = new Date(result.solar.getYear(), result.solar.getMonth() - 1, result.solar.getDay(), originalHours, originalMinutes);
    } else {
      // 无法解析农历日期，使用原始公历日期作为后备
      targetDate = new Date(originalYear, originalMonth, originalDay, originalHours, originalMinutes);
    }
  } else {
    // 公历日期
    targetDate = new Date(originalYear, originalMonth, originalDay, originalHours, originalMinutes);
  }

  // 先判断是否今天（日期部分相等）
  const isToday = targetDate.toDateString() === today.toDateString();

  // 计算下一个 occurrence
  if (repeatType === 'yearly') {
    if (isLunar && lunarMonth !== null && lunarDay !== null) {
      // 农历年度重复：根据农历日期查找今年或明年的对应公历日期
      const thisYearResult = safeCreateLunarDate(today.getFullYear(), lunarMonth, lunarDay);
      if (thisYearResult) {
        targetDate = new Date(thisYearResult.solar.getYear(), thisYearResult.solar.getMonth() - 1, thisYearResult.solar.getDay(), originalHours, originalMinutes);
      }
      // 如果今年的农历日期已过，查找明年
      if (!targetDate || targetDate < today) {
        const nextYearResult = safeCreateLunarDate(today.getFullYear() + 1, lunarMonth, lunarDay);
        if (nextYearResult) {
          targetDate = new Date(nextYearResult.solar.getYear(), nextYearResult.solar.getMonth() - 1, nextYearResult.solar.getDay(), originalHours, originalMinutes);
        }
      }
    } else {
      // 公历年度重复：找到今年或明年的对应日期
      targetDate = safeCreateDate(today.getFullYear(), targetDate.getMonth(), targetDate.getDate());
      targetDate.setHours(originalHours, originalMinutes, 0, 0);
      if (targetDate < today) {
        targetDate = safeCreateDate(today.getFullYear() + 1, targetDate.getMonth(), targetDate.getDate());
        targetDate.setHours(originalHours, originalMinutes, 0, 0);
      }
    }
  } else if (repeatType === 'monthly') {
    // 月度重复：找到本月或之后月份的对应日期
    const originalDay = targetDate.getDate();
    let currentMonth = today.getMonth(); // 从当前月份开始
    targetDate = safeCreateDate(today.getFullYear(), currentMonth, originalDay);
    targetDate.setHours(originalHours, originalMinutes, 0, 0);

    // 持续递增月份直到找到未来日期
    while (targetDate < today) {
      currentMonth++;
      targetDate = safeCreateDate(today.getFullYear(), currentMonth, originalDay);
      targetDate.setHours(originalHours, originalMinutes, 0, 0);
    }
  } else if (repeatType === 'daily') {
    // 每日重复：找到今天或明天的对应时间点
    targetDate = new Date(today);
    targetDate.setHours(originalHours, originalMinutes, 0, 0);
    if (targetDate < now) {
      targetDate = new Date(today);
      targetDate.setDate(targetDate.getDate() + 1);
      targetDate.setHours(originalHours, originalMinutes, 0, 0);
    }
  } else if (repeatType === 'weekly') {
    // 每周重复：找到本周或下周对应星期几的时间点
    const dayOfWeek = new Date(originalYear, originalMonth, originalDay).getDay();
    targetDate = new Date(today);
    const daysUntilTarget = (dayOfWeek - today.getDay() + 7) % 7;
    targetDate.setDate(targetDate.getDate() + daysUntilTarget);
    targetDate.setHours(originalHours, originalMinutes, 0, 0);
    if (targetDate < now) {
      targetDate.setDate(targetDate.getDate() + 7);
    }
  } else {
    // 不重复
    if (targetDate < today) {
      isPast = true;
    }
  }

  // 计算时间差
  const diff = targetDate.getTime() - now.getTime();

  // 如果是今天，即使是负数（已过），也显示为 0 而不是"已过"
  // 只要 isToday 为 true，就不算"已过"，显示为"今天"
  if (diff < 0 && !isPast) {
    if (!isToday) {
      isPast = true;
    }
  }

  const absDiff = Math.abs(diff);
  // 如果是今天，直接返回0天
  let days: number;
  let hours = 0;
  let minutes = 0;
  let seconds = 0;

  if (isToday) {
    days = 0;
    hours = 0;
    minutes = 0;
    seconds = 0;
    isPast = false; // 今天不算已过
  } else {
    // 使用 ceil 来计算天数，这样用户看到的是"还有X天"的直观感受
    // 例如：2/12 18:00 到 2/15 00:00 应该显示"还有3天"而不是"还有2天"
    days = Math.ceil(absDiff / (1000 * 60 * 60 * 24));
    // 重新计算剩余的小时、分钟、秒（使用 ceil 后剩余时间需要调整）
    const remainingAfterDays = absDiff - (days - 1) * (1000 * 60 * 60 * 24);
    hours = Math.floor((remainingAfterDays % (1000 * 60 * 60 * 24)) / (1000 * 60 * 60));
    minutes = Math.floor((remainingAfterDays % (1000 * 60 * 60)) / (1000 * 60));
    seconds = Math.floor((remainingAfterDays % (1000 * 60)) / 1000);
  }

  return {
    days: isPast ? -days : days,
    hours,
    minutes,
    seconds,
    nextDate: targetDate,
    isToday,
    isPast,
  };
}

/**
 * 格式化倒计时显示
 */
export function formatCountdown(countdown: CountdownResult): string {
  if (countdown.isPast) {
    return '已过';
  }

  if (countdown.isToday) {
    return '今天';
  }

  if (countdown.days > 0) {
    return `${countdown.days}天`;
  }

  if (countdown.hours > 0) {
    return `${countdown.hours}时${countdown.minutes}分`;
  }

  return `${countdown.minutes}分${countdown.seconds}秒`;
}

/**
 * 获取友好的日期描述
 */
export function getFriendlyDateDescription(
  dateStr: string,
  repeatType: 'yearly' | 'monthly' | 'daily' | 'weekly' | 'none',
  isLunar: boolean
): string {
  const countdown = calculateCountdown(dateStr, repeatType, isLunar);
  const targetDate = countdown.nextDate;

  if (countdown.isPast) {
    return '已过';
  }

  if (countdown.isToday) {
    return '今天';
  }

  const now = new Date();
  const tomorrow = new Date(now);
  tomorrow.setDate(tomorrow.getDate() + 1);

  if (targetDate.toDateString() === tomorrow.toDateString()) {
    return '明天';
  }

  if (countdown.days < 7) {
    return `${countdown.days}天后`;
  }

  // 返回格式化日期
  const month = targetDate.getMonth() + 1;
  const day = targetDate.getDate();

  if (isLunar) {
    // 显示农历
    const result = safeCreateLunarDate(targetDate.getFullYear(), month, day);
    if (result) {
      return `${result.lunar.getMonthInChinese()}月${result.lunar.getDayInChinese()}`;
    }
    return `${month}月${day}日`;
  }

  return `${month}月${day}日`;
}

/**
 * 获取农历日期的公历日期
 */
export function getSolarFromLunar(lunarMonth: number, lunarDay: number, year?: number): Date {
  const targetYear = year || new Date().getFullYear();
  const lunar = Lunar.fromYmd(targetYear, lunarMonth, lunarDay);
  const solar = lunar.getSolar();
  return new Date(solar.getYear(), solar.getMonth() - 1, solar.getDay());
}

/**
 * 获取公历日期的农历日期
 */
export function getLunarFromSolar(solarDate: Date): { month: number; day: number; monthInChinese: string; dayInChinese: string } {
  const lunar = Lunar.fromYmd(solarDate.getFullYear(), solarDate.getMonth() + 1, solarDate.getDate());
  return {
    month: lunar.getMonth(),
    day: lunar.getDay(),
    monthInChinese: lunar.getMonthInChinese(),
    dayInChinese: lunar.getDayInChinese(),
  };
}