import {
  addShanghaiDays,
  parseShanghaiYmd,
  shanghaiMonthRange,
  shanghaiWeekRange,
  shanghaiYearMonth,
  shanghaiYmd,
  startOfShanghaiDay,
} from './shanghai-date';

export const DASHBOARD_GRANULARITIES = ['day', 'week', 'month', 'quarter', 'year'] as const;
export type DashboardGranularity = (typeof DASHBOARD_GRANULARITIES)[number];

function pad2(n: number): string {
  return String(n).padStart(2, '0');
}

export function shanghaiQuarterIndex(d: Date): { year: number; quarter: number } {
  const [y, m] = shanghaiYmd(d).split('-').map(Number);
  return { year: y, quarter: Math.ceil(m / 3) };
}

export function shanghaiQuarterRange(
  year: number,
  quarter: number,
): { start: Date; endExclusive: Date } {
  const startMonth = (quarter - 1) * 3 + 1;
  const endMonth = startMonth + 3;
  const endYear = endMonth > 12 ? year + 1 : year;
  const em = endMonth > 12 ? endMonth - 12 : endMonth;
  return {
    start: new Date(`${year}-${pad2(startMonth)}-01T00:00:00+08:00`),
    endExclusive: new Date(`${endYear}-${pad2(em)}-01T00:00:00+08:00`),
  };
}

export function shanghaiBucketKey(d: Date, grain: DashboardGranularity): string {
  const ymd = shanghaiYmd(d);
  const [y, m] = ymd.split('-').map(Number);
  switch (grain) {
    case 'day':
      return ymd;
    case 'week':
      return shanghaiYmd(shanghaiWeekRange(d).start);
    case 'month':
      return `${y}-${pad2(m)}`;
    case 'quarter':
      return `${y}-Q${Math.ceil(m / 3)}`;
    case 'year':
      return String(y);
  }
}

export function shanghaiBucketLabel(key: string, grain: DashboardGranularity): string {
  switch (grain) {
    case 'day':
      return key.slice(5);
    case 'week':
      return `${key.slice(5)}周`;
    default:
      return key;
  }
}

export type ShanghaiBucket = {
  key: string;
  label: string;
  start: Date;
  endExclusive: Date;
};

export function eachShanghaiBuckets(
  from: Date,
  to: Date,
  grain: DashboardGranularity,
): ShanghaiBucket[] {
  const startDay = startOfShanghaiDay(from);
  const endDay = startOfShanghaiDay(to);
  const out: ShanghaiBucket[] = [];

  if (grain === 'day') {
    for (let d = startDay; d.getTime() <= endDay.getTime(); d = addShanghaiDays(d, 1)) {
      const key = shanghaiYmd(d);
      out.push({
        key,
        label: shanghaiBucketLabel(key, grain),
        start: d,
        endExclusive: addShanghaiDays(d, 1),
      });
    }
    return out;
  }

  if (grain === 'week') {
    let { start } = shanghaiWeekRange(startDay);
    const lastStart = shanghaiWeekRange(endDay).start;
    while (start.getTime() <= lastStart.getTime()) {
      const key = shanghaiYmd(start);
      const endExclusive = addShanghaiDays(start, 7);
      out.push({ key, label: shanghaiBucketLabel(key, grain), start, endExclusive });
      start = endExclusive;
    }
    return out;
  }

  if (grain === 'month') {
    let { year, month } = shanghaiYearMonth(startDay);
    const end = shanghaiYearMonth(endDay);
    while (year < end.year || (year === end.year && month <= end.month)) {
      const range = shanghaiMonthRange(year, month);
      const key = `${year}-${pad2(month)}`;
      out.push({ key, label: key, start: range.start, endExclusive: range.endExclusive });
      month += 1;
      if (month > 12) {
        month = 1;
        year += 1;
      }
    }
    return out;
  }

  if (grain === 'quarter') {
    let { year, quarter } = shanghaiQuarterIndex(startDay);
    const end = shanghaiQuarterIndex(endDay);
    while (year < end.year || (year === end.year && quarter <= end.quarter)) {
      const range = shanghaiQuarterRange(year, quarter);
      const key = `${year}-Q${quarter}`;
      out.push({ key, label: key, start: range.start, endExclusive: range.endExclusive });
      quarter += 1;
      if (quarter > 4) {
        quarter = 1;
        year += 1;
      }
    }
    return out;
  }

  let year = Number(shanghaiYmd(startDay).slice(0, 4));
  const endYear = Number(shanghaiYmd(endDay).slice(0, 4));
  while (year <= endYear) {
    out.push({
      key: String(year),
      label: String(year),
      start: new Date(`${year}-01-01T00:00:00+08:00`),
      endExclusive: new Date(`${year + 1}-01-01T00:00:00+08:00`),
    });
    year += 1;
  }
  return out;
}

/** 按粒度把日期往前挪一档（日/周/月/季/年），用于环比窗口 */
export function addShanghaiGrain(d: Date, grain: DashboardGranularity, delta: number): Date {
  const start = startOfShanghaiDay(d);
  switch (grain) {
    case 'day':
      return addShanghaiDays(start, delta);
    case 'week':
      return addShanghaiDays(start, delta * 7);
    case 'month':
      return addShanghaiMonths(start, delta);
    case 'quarter':
      return addShanghaiMonths(start, delta * 3);
    case 'year':
      return addShanghaiMonths(start, delta * 12);
  }
}

function addShanghaiMonths(d: Date, delta: number): Date {
  const [y, m, day] = shanghaiYmd(d).split('-').map(Number);
  const utc = new Date(Date.UTC(y, m - 1 + delta, 1));
  const ty = utc.getUTCFullYear();
  const tm = utc.getUTCMonth() + 1;
  const last = new Date(Date.UTC(ty, tm, 0)).getUTCDate();
  return parseShanghaiYmd(`${ty}-${pad2(tm)}-${pad2(Math.min(day, last))}`);
}

/** 整段起止按粒度回退一档：日窗口昨天~今天 → 前天~昨天 */
export function previousShanghaiRangeByGrain(
  from: Date,
  to: Date,
  grain: DashboardGranularity,
): { from: Date; to: Date } {
  return {
    from: addShanghaiGrain(from, grain, -1),
    to: addShanghaiGrain(to, grain, -1),
  };
}

/** 环比：(本期 − 上期) / 上期；上期 0 且本期 0 → null；上期 0 且本期 > 0 → 1 */
export function periodMomRatio(curr: number, prev: number): number | null {
  if (prev === 0) return curr === 0 ? null : 1;
  return (curr - prev) / prev;
}

/** 默认窗口 = 上一档起点 ～ 今天（日=昨天~今天，周=上周一~今天，以此类推） */
export function defaultShanghaiRange(
  grain: DashboardGranularity,
  anchor = new Date(),
): { from: Date; to: Date } {
  const to = startOfShanghaiDay(anchor);
  switch (grain) {
    case 'day':
      return { from: addShanghaiDays(to, -1), to };
    case 'week': {
      const thisMonday = shanghaiWeekRange(to).start;
      return { from: addShanghaiDays(thisMonday, -7), to };
    }
    case 'month': {
      const { year, month } = shanghaiYearMonth(to);
      const prev = month === 1 ? { year: year - 1, month: 12 } : { year, month: month - 1 };
      return { from: shanghaiMonthRange(prev.year, prev.month).start, to };
    }
    case 'quarter': {
      const { year, quarter } = shanghaiQuarterIndex(to);
      let y = year;
      let q = quarter - 1;
      if (q <= 0) {
        q = 4;
        y -= 1;
      }
      return { from: shanghaiQuarterRange(y, q).start, to };
    }
    case 'year': {
      const y = Number(shanghaiYmd(to).slice(0, 4));
      return { from: new Date(`${y - 1}-01-01T00:00:00+08:00`), to };
    }
  }
}

export function defaultShanghaiRangeYmds(
  grain: DashboardGranularity,
  anchor = new Date(),
): { from: string; to: string } {
  const r = defaultShanghaiRange(grain, anchor);
  return { from: shanghaiYmd(r.from), to: shanghaiYmd(r.to) };
}