import dayjs, { Dayjs } from 'dayjs';
import 'dayjs/locale/en';
import 'dayjs/locale/zh-cn';
import { MenstrualFlowSample } from './health';

export type MenstrualDayStatus = 'period' | 'predicted-period' | 'fertile' | 'ovulation-day';

export type CycleRecord = {
  startDate: string;
  periodLength?: number;
  cycleLength?: number;
  source?: 'healthkit' | 'manual';
};

export type MenstrualDayInfo = {
  date: Dayjs;
  status: MenstrualDayStatus;
  confirmed: boolean;
  dayOfCycle?: number;
};

export type MenstrualDayCell =
  | {
      type: 'placeholder';
      key: string;
    }
  | {
      type: 'day';
      key: string;
      label: number;
      date: Dayjs;
      info?: MenstrualDayInfo;
      isToday: boolean;
    };

export type MenstrualMonth = {
  id: string;
  title: string;
  subtitle: string;
  cells: MenstrualDayCell[];
};

export type MenstrualTimeline = {
  months: MenstrualMonth[];
  dayMap: Record<string, MenstrualDayInfo>;
  cycleLength: number;
  periodLength: number;
  todayInfo?: MenstrualDayInfo;
};

const STATUS_PRIORITY: Record<MenstrualDayStatus, number> = {
  'ovulation-day': 4,
  period: 3,
  'predicted-period': 2,
  fertile: 1,
};

export const DEFAULT_CYCLE_LENGTH = 28;
export const DEFAULT_PERIOD_LENGTH = 5;
const MIN_CYCLE_LENGTH = 21;
const MAX_CYCLE_LENGTH = 45;
const LOOKBACK_WINDOW = 6;
const LUTEAL_PHASE_MEAN = 13; // 12–14 天之间较为稳定

const clampCycleLength = (value: number, fallback: number) => {
  if (!Number.isFinite(value) || value <= 0) return fallback;
  return Math.max(MIN_CYCLE_LENGTH, Math.min(MAX_CYCLE_LENGTH, Math.round(value)));
};

const calcMedian = (values: number[]) => {
  if (!values.length) return undefined;
  const sorted = [...values].sort((a, b) => a - b);
  const mid = Math.floor(sorted.length / 2);
  if (sorted.length % 2 === 0) {
    return (sorted[mid - 1] + sorted[mid]) / 2;
  }
  return sorted[mid];
};

const calcTrimmedMean = (values: number[], trim = 1) => {
  if (!values.length) return undefined;
  const sorted = [...values].sort((a, b) => a - b);
  const start = Math.min(trim, sorted.length);
  const end = Math.max(sorted.length - trim, start);
  const sliced = sorted.slice(start, end);
  if (!sliced.length) return undefined;
  return sliced.reduce((sum, cur) => sum + cur, 0) / sliced.length;
};

const calcStdDev = (values: number[]) => {
  if (values.length < 2) return 0;
  const mean = values.reduce((s, v) => s + v, 0) / values.length;
  const variance =
    values.reduce((s, v) => s + (v - mean) * (v - mean), 0) / (values.length - 1);
  return Math.sqrt(variance);
};

const calcAverageCycleLength = (records: CycleRecord[], fallback = DEFAULT_CYCLE_LENGTH) => {
  if (records.length < 2) return fallback;
  const sorted = [...records].sort(
    (a, b) => dayjs(a.startDate).valueOf() - dayjs(b.startDate).valueOf()
  );
  const intervals: number[] = [];
  for (let i = 1; i < sorted.length; i += 1) {
    const diff = dayjs(sorted[i].startDate).diff(dayjs(sorted[i - 1].startDate), 'day');
    if (diff > 0) {
      intervals.push(diff);
    }
  }
  if (!intervals.length) return fallback;
  const recent = intervals.slice(-LOOKBACK_WINDOW);
  const median = calcMedian(recent);
  const trimmed = calcTrimmedMean(recent);
  const blended = median ?? trimmed ?? calcTrimmedMean(intervals) ?? fallback;
  return clampCycleLength(blended, fallback);
};

const calcAveragePeriodLength = (records: CycleRecord[], fallback = DEFAULT_PERIOD_LENGTH) => {
  const lengths = records
    .map((r) => r.periodLength)
    .filter((l): l is number => typeof l === 'number' && l > 0);
  if (!lengths.length) return fallback;
  const recent = lengths.slice(-LOOKBACK_WINDOW);
  const median = calcMedian(recent);
  const trimmed = calcTrimmedMean(recent);
  const blended = median ?? trimmed ?? calcTrimmedMean(lengths) ?? fallback;
  return Math.max(3, Math.round(blended)); // 极端短周期时仍保持生理期合理下限
};

const addDayInfo = (
  dayMap: Record<string, MenstrualDayInfo>,
  date: Dayjs,
  info: MenstrualDayInfo
) => {
  const key = date.format('YYYY-MM-DD');
  const existing = dayMap[key];

  if (existing && STATUS_PRIORITY[existing.status] >= STATUS_PRIORITY[info.status]) {
    return;
  }

  dayMap[key] = info;
};

const getOvulationDay = (cycleStart: Dayjs, cycleLength: number) => {
  // 排卵日约在下次月经前 12-14 天，较稳定；对极端周期做边界约束
  const daysFromStart = cycleLength - LUTEAL_PHASE_MEAN;
  const offset = Math.min(Math.max(daysFromStart, 11), 16);
  return cycleStart.add(offset, 'day');
};

export const buildMenstrualTimeline = (options?: {
  records?: CycleRecord[];
  monthsBefore?: number;
  monthsAfter?: number;
  defaultCycleLength?: number;
  defaultPeriodLength?: number;
  locale?: 'zh' | 'en';
  monthTitleFormat?: string;
  monthSubtitleFormat?: string;
}): MenstrualTimeline => {
  const today = dayjs();
  const monthsBefore = options?.monthsBefore ?? 2;
  const monthsAfter = options?.monthsAfter ?? 3;
  const startMonth = today.subtract(monthsBefore, 'month').startOf('month');
  const endMonth = today.add(monthsAfter, 'month').endOf('month');

  const records = (options?.records ?? []).sort(
    (a, b) => dayjs(a.startDate).valueOf() - dayjs(b.startDate).valueOf()
  );

  const avgCycleLength =
    options?.defaultCycleLength ?? calcAverageCycleLength(records, DEFAULT_CYCLE_LENGTH);
  const avgPeriodLength =
    options?.defaultPeriodLength ?? calcAveragePeriodLength(records, DEFAULT_PERIOD_LENGTH);
  const sortedStarts = [...records]
    .sort((a, b) => dayjs(a.startDate).valueOf() - dayjs(b.startDate).valueOf())
    .map((r) => dayjs(r.startDate));
  const cycleIntervals: number[] = [];
  for (let i = 1; i < sortedStarts.length; i += 1) {
    const diff = sortedStarts[i].diff(sortedStarts[i - 1], 'day');
    if (diff > 0) cycleIntervals.push(diff);
  }
  const recentIntervals = cycleIntervals.slice(-LOOKBACK_WINDOW);
  const cycleVariability = calcStdDev(recentIntervals);
  const lastInterval =
    recentIntervals.length > 0 ? recentIntervals[recentIntervals.length - 1] : avgCycleLength;
  // 对未来预测使用稳健均值 + 最新趋势的折中，以避免单次异常牵动过大
  const predictedCycleLength = clampCycleLength(
    0.55 * avgCycleLength + 0.45 * lastInterval,
    avgCycleLength
  );

  const cycles = records.map((record) => ({
    start: dayjs(record.startDate),
    confirmed: true,
    periodLength: record.periodLength ?? avgPeriodLength,
    cycleLength: record.cycleLength ?? avgCycleLength,
  }));

  // 基于真实相邻开始日期矫正已记录周期长度，便于后续计算排卵日/易孕期
  for (let i = 0; i < cycles.length; i += 1) {
    const next = cycles[i + 1];
    if (next) {
      const interval = next.start.diff(cycles[i].start, 'day');
      if (interval > 0) {
        cycles[i].cycleLength = clampCycleLength(interval, cycles[i].cycleLength);
      }
    }
  }

  // 只有当存在历史记录时，才进行后续预测
  if (cycles.length > 0) {
    const lastConfirmed = cycles[cycles.length - 1];
    let cursorStart = lastConfirmed.start;
    let nextCycleLength = predictedCycleLength;

    while (cursorStart.isBefore(endMonth)) {
      cursorStart = cursorStart.add(nextCycleLength, 'day');
      cycles.push({
        start: cursorStart,
        confirmed: false,
        periodLength: avgPeriodLength,
        cycleLength: nextCycleLength,
      });
      // 趋势逐步回归稳健均值，避免长期漂移
      nextCycleLength = clampCycleLength(
        Math.round(nextCycleLength * 0.65 + avgCycleLength * 0.35),
        avgCycleLength
      );
    }
  }

  const dayMap: Record<string, MenstrualDayInfo> = {};

  cycles.forEach((cycle) => {
    const ovulationDay = getOvulationDay(cycle.start, cycle.cycleLength);
    // 经前 luteal 稳定，易孕窗口 5-7 天：排卵日前 5 天 + 排卵日当日；高波动人群额外向前扩 1 天
    const fertileWindow = Math.min(7, 6 + (cycle.confirmed ? 0 : Math.round(cycleVariability)));
    const fertileStart = ovulationDay.subtract(fertileWindow, 'day');

    for (let i = 0; i < cycle.periodLength; i += 1) {
      const date = cycle.start.add(i, 'day');
      if (date.isBefore(startMonth) || date.isAfter(endMonth)) continue;
      addDayInfo(dayMap, date, {
        date,
        status: cycle.confirmed ? 'period' : 'predicted-period',
        confirmed: cycle.confirmed,
        dayOfCycle: i + 1,
      });
    }

    for (let i = 0; i < fertileWindow; i += 1) {
      const date = fertileStart.add(i, 'day');
      if (date.isBefore(startMonth) || date.isAfter(endMonth)) continue;
      addDayInfo(dayMap, date, {
        date,
        status: 'fertile',
        confirmed: cycle.confirmed,
      });
    }

    if (!ovulationDay.isBefore(startMonth) && !ovulationDay.isAfter(endMonth)) {
      addDayInfo(dayMap, ovulationDay, {
        date: ovulationDay,
        status: 'ovulation-day',
        confirmed: cycle.confirmed,
      });
    }
  });

  const months: MenstrualMonth[] = [];
  let monthCursor = startMonth.startOf('month');

  const locale = options?.locale ?? 'zh';
  const localeKey = locale === 'en' ? 'en' : 'zh-cn';
  const monthTitleFormat = options?.monthTitleFormat ?? (locale === 'en' ? 'MMM' : 'M月');
  const monthSubtitleFormat = options?.monthSubtitleFormat ?? (locale === 'en' ? 'YYYY' : 'YYYY年');

  while (monthCursor.isBefore(endMonth) || monthCursor.isSame(endMonth, 'month')) {
    const firstDay = monthCursor.startOf('month');
    const daysInMonth = firstDay.daysInMonth();
    // 以周一为周首，符合设计稿呈现
    const firstWeekday = (firstDay.day() + 6) % 7; // 0(一) - 6(日)
    const cells: MenstrualDayCell[] = [];

    for (let i = 0; i < firstWeekday; i += 1) {
      cells.push({ type: 'placeholder', key: `${firstDay.format('YYYY-MM')}-p-${i}` });
    }

    for (let day = 1; day <= daysInMonth; day += 1) {
      const date = firstDay.date(day);
      const key = date.format('YYYY-MM-DD');
      cells.push({
        type: 'day',
        key,
        label: day,
        date,
        info: dayMap[key],
        isToday: date.isSame(today, 'day'),
      });
    }

    while (cells.length % 7 !== 0) {
      cells.push({
        type: 'placeholder',
        key: `${firstDay.format('YYYY-MM')}-t-${cells.length}`,
      });
    }

    const formattedMonth = firstDay.locale(localeKey);

    months.push({
      id: firstDay.format('YYYY-MM'),
      title: formattedMonth.format(monthTitleFormat),
      subtitle: formattedMonth.format(monthSubtitleFormat),
      cells,
    });

    monthCursor = monthCursor.add(1, 'month');
  }

  const todayKey = today.format('YYYY-MM-DD');

  return {
    months,
    dayMap,
    cycleLength: predictedCycleLength,
    periodLength: avgPeriodLength,
    todayInfo: dayMap[todayKey],
  };
};

export const getMenstrualSummaryForDate = (
  date: Dayjs,
  dayMap: Record<string, MenstrualDayInfo>
) => {
  const key = date.format('YYYY-MM-DD');
  return dayMap[key];
};

export const convertHealthKitSamplesToCycleRecords = (
  samples: MenstrualFlowSample[]
): CycleRecord[] => {
  if (!samples.length) return [];

  // 1. Sort samples by date
  const sortedSamples = [...samples].sort(
    (a, b) => dayjs(a.startDate).valueOf() - dayjs(b.startDate).valueOf()
  );

  const records: CycleRecord[] = [];
  let currentStart: Dayjs | null = null;
  let currentEnd: Dayjs | null = null;

  // 2. Iterate and merge consecutive days
  for (const sample of sortedSamples) {
    const sampleDate = dayjs(sample.startDate);

    // If we have no current period being tracked, start a new one
    if (!currentStart) {
      currentStart = sampleDate;
      currentEnd = sampleDate;
      continue;
    }

    // Check if this sample is contiguous with the current period
    // Allow 1 day gap? Standard logic usually assumes contiguous days for a single period.
    // However, spotting might cause gaps. For now, we'll merge if gap <= 1 day.
    const diff = sampleDate.diff(currentEnd, 'day');

    if (diff <= 1) {
      // Extend current period
      currentEnd = sampleDate;
    } else {
      // Gap is too large, finalize current period and start new one
      if (currentStart && currentEnd) {
        records.push({
          startDate: currentStart.format('YYYY-MM-DD'),
          periodLength: currentEnd.diff(currentStart, 'day') + 1,
          source: 'healthkit',
        });
      }
      currentStart = sampleDate;
      currentEnd = sampleDate;
    }
  }

  // Push the last record
  if (currentStart && currentEnd) {
    records.push({
      startDate: currentStart.format('YYYY-MM-DD'),
      periodLength: currentEnd.diff(currentStart, 'day') + 1,
      source: 'healthkit',
    });
  }

  return records;
};