const TZ_OFFSET_MIN = Number(process.env.TEMPORAL_RECALL_TZ_OFFSET_MIN ?? 480);

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

/** @param {Date} d */
function toLocalParts(d) {
  const shifted = new Date(d.getTime() + TZ_OFFSET_MIN * 60_000);
  return {
    year: shifted.getUTCFullYear(),
    month: shifted.getUTCMonth(),
    day: shifted.getUTCDate(),
    dow: shifted.getUTCDay(),
    hour: shifted.getUTCHours(),
  };
}

/** @param {{ year: number, month: number, day: number }} p @param {number} h @param {number} m */
function partsToIso(p, h = 0, m = 0) {
  const utcMs =
    Date.UTC(p.year, p.month, p.day, h, m, 0, 0) - TZ_OFFSET_MIN * 60_000;
  return new Date(utcMs).toISOString();
}

/** @param {Date} anchor */
function startOfDay(anchor) {
  const p = toLocalParts(anchor);
  return new Date(partsToIso(p, 0, 0));
}

/** @param {Date} anchor */
function endOfDay(anchor) {
  const p = toLocalParts(anchor);
  const start = Date.UTC(p.year, p.month, p.day + 1, 0, 0, 0, 0) - TZ_OFFSET_MIN * 60_000;
  return new Date(start);
}

/** @param {Date} anchor @param {number} deltaDays */
function addDays(anchor, deltaDays) {
  const p = toLocalParts(anchor);
  const ms = Date.UTC(p.year, p.month, p.day + deltaDays, 0, 0, 0, 0) - TZ_OFFSET_MIN * 60_000;
  return new Date(ms);
}

/** @param {Date} anchor */
function startOfWeek(anchor) {
  const p = toLocalParts(anchor);
  const mondayOffset = p.dow === 0 ? -6 : 1 - p.dow;
  const ms =
    Date.UTC(p.year, p.month, p.day + mondayOffset, 0, 0, 0, 0) -
    TZ_OFFSET_MIN * 60_000;
  return new Date(ms);
}

/** @param {Date} anchor */
function endOfWeek(anchor) {
  const start = startOfWeek(anchor);
  return addDays(start, 7);
}

/** @param {Date} anchor */
function startOfMonth(anchor) {
  const p = toLocalParts(anchor);
  return new Date(Date.UTC(p.year, p.month, 1, 0, 0, 0, 0) - TZ_OFFSET_MIN * 60_000);
}

/** @param {Date} anchor */
function endOfMonth(anchor) {
  const p = toLocalParts(anchor);
  return new Date(Date.UTC(p.year, p.month + 1, 1, 0, 0, 0, 0) - TZ_OFFSET_MIN * 60_000);
}

/**
 * @param {string} query
 * @param {Date} [now]
 * @returns {{ mention_range: { start: string, end: string }, event_range: { start: string, end: string } | null, relative_label: string | null, rule_hits: string[] }}
 */
export function parseTimeScope(query, now = new Date()) {
  const text = String(query ?? '');
  const rule_hits = [];
  let relative_label = null;
  let rangeStart = null;
  let rangeEnd = null;

  const patterns = [
    { re: /前天/, label: 'day_before_yesterday', apply: () => {
      const d = addDays(now, -2);
      return [startOfDay(d), endOfDay(d)];
    }},
    { re: /昨天|昨日/, label: 'yesterday', apply: () => {
      const d = addDays(now, -1);
      return [startOfDay(d), endOfDay(d)];
    }},
    { re: /今天|今日/, label: 'today', apply: () => [startOfDay(now), endOfDay(now)] },
    { re: /明天|明日/, label: 'tomorrow', apply: () => {
      const d = addDays(now, 1);
      return [startOfDay(d), endOfDay(d)];
    }},
    { re: /后天/, label: 'day_after_tomorrow', apply: () => {
      const d = addDays(now, 2);
      return [startOfDay(d), endOfDay(d)];
    }},
    { re: /上周|上星期|上个星期/, label: 'last_week', apply: () => {
      const thisWeek = startOfWeek(now);
      const lastStart = addDays(thisWeek, -7);
      return [lastStart, thisWeek];
    }},
    { re: /这周|本周|这个星期|这星期/, label: 'this_week', apply: () => [startOfWeek(now), endOfWeek(now)] },
    { re: /上个月/, label: 'last_month', apply: () => {
      const thisMonth = startOfMonth(now);
      const p = toLocalParts(thisMonth);
      const lastStart = new Date(Date.UTC(p.year, p.month - 1, 1, 0, 0, 0, 0) - TZ_OFFSET_MIN * 60_000);
      return [lastStart, thisMonth];
    }},
    { re: /这个月|本月/, label: 'this_month', apply: () => [startOfMonth(now), endOfMonth(now)] },
    { re: /最近(\d+)天/, label: 'recent_days', apply: (m) => {
      const days = Number(m[1]);
      return [addDays(now, -days), endOfDay(now)];
    }},
    { re: /最近一周|最近1周/, label: 'recent_week', apply: () => [addDays(now, -7), endOfDay(now)] },
  ];

  for (const { re, label, apply } of patterns) {
    const m = text.match(re);
    if (m) {
      [rangeStart, rangeEnd] = apply(m);
      relative_label = label;
      rule_hits.push(`time:${label}`);
      break;
    }
  }

  if (!rangeStart) {
    if (/最近|近期|这几天/.test(text)) {
      [rangeStart, rangeEnd] = [addDays(now, -7), endOfDay(now)];
      relative_label = 'recent_week';
      rule_hits.push('time:recent_fuzzy');
    } else {
      [rangeStart, rangeEnd] = [addDays(now, -7), endOfDay(now)];
      relative_label = 'this_week';
      rule_hits.push('time:default_week');
    }
  }

  const mention_range = {
    start: rangeStart.toISOString(),
    end: rangeEnd.toISOString(),
  };

  let event_range = null;
  if (/安排|行程|会议|约会|几点|日历/.test(text)) {
    event_range = { ...mention_range };
    rule_hits.push('time:event_range_linked');
  }

  return { mention_range, event_range, relative_label, rule_hits };
}