// Compute which Kimai entries to create so that, per day, Kimai total == Abacus total.
//
// For each day:
//   need  = abacus minutes - minutes already in Kimai
//   slots = abacus intervals (or [dayStart, 24:00] if only a total is known) minus existing Kimai entries
//   1. fixed recurring rules (with start time first, then the others)
//   2. the rest goes to the "remainder" rule of that day, or the default project/activity
var Planner = (() => {
  function ruleApplies(rule, date) {
    if (!rule.enabled) return false;
    if (rule.validFrom && date < rule.validFrom) return false;
    if (rule.validTo && date > rule.validTo) return false;
    if (!(rule.weekdays || []).includes(U.weekday(date))) return false;
    const n = +rule.everyNWeeks || 1;
    if (n > 1) {
      const w = U.weeksBetween(rule.anchorDate || '2026-01-05', date);
      if (((w % n) + n) % n !== 0) return false;
    }
    return true;
  }

  // Carve `minutes` out of free slots (mutates slots). Starts at `from` when given.
  function take(slots, minutes, from = null) {
    const pieces = [];
    let left = minutes;
    for (let i = 0; i < slots.length && left > 0; i++) {
      const s = slots[i];
      const st = from != null ? Math.max(s.start, from) : s.start;
      if (st >= s.end) continue;
      const en = Math.min(s.end, st + left);
      pieces.push({ start: st, end: en });
      left -= en - st;
      const repl = [];
      if (s.start < st) repl.push({ start: s.start, end: st });
      if (en < s.end) repl.push({ start: en, end: s.end });
      slots.splice(i, 1, ...repl);
      i += repl.length - 1;
    }
    return { pieces, left };
  }

  function subtract(slots, busy) {
    let out = slots.map((s) => ({ ...s }));
    for (const b of busy) {
      out = out.flatMap((s) => {
        if (b.end <= s.start || b.start >= s.end) return [s];
        const r = [];
        if (s.start < b.start) r.push({ start: s.start, end: b.start });
        if (b.end < s.end) r.push({ start: b.end, end: s.end });
        return r;
      });
    }
    return out;
  }

  /**
   * days:     [{date, intervals, minutes}]
   * existing: Map date -> [{start, end, project, activity}]
   * rules:    recurring rules
   * settings: {defaultProject, defaultActivity, defaultDescription, dayStart, skipIfRulePresent}
   */
  function plan(days, existing, rules, settings) {
    const dayStart = U.toMin(settings.dayStart) ?? 8 * 60;

    return days.map((day) => {
      const ex = existing.get(day.date) || [];
      const existingMin = ex.reduce((a, e) => a + (e.end - e.start), 0);
      const res = { date: day.date, target: day.minutes, existingMin, existing: ex, entries: [], warnings: [] };
      let need = day.minutes - existingMin;
      if (need < 0) res.warnings.push(`Kimai has ${U.fmtDur(-need)} more than Abacus`);
      if (need <= 0) return finish(res);

      const base = day.intervals.length ? day.intervals : [{ start: dayStart, end: 24 * 60 }];
      const slots = subtract(base, [...ex].sort((a, b) => a.start - b.start));

      const applicable = rules.filter((r) => ruleApplies(r, day.date));
      const fixed = applicable
        .filter((r) => +r.minutes > 0)
        .sort((a, b) => (a.startTime ? 0 : 1) - (b.startTime ? 0 : 1) || (U.toMin(a.startTime) || 0) - (U.toMin(b.startTime) || 0));
      const remainder = applicable.find((r) => !(+r.minutes > 0));

      const push = (pieces, src) => {
        for (const p of pieces) {
          res.entries.push({
            start: p.start, end: p.end,
            project: src.project, activity: src.activity,
            projectLabel: src.projectLabel, activityLabel: src.activityLabel,
            description: src.description || '', source: src.name || 'default',
          });
        }
      };

      for (const r of fixed) {
        if (need <= 0) break;
        if (settings.skipIfRulePresent && ex.some((e) => e.project == r.project && e.activity == r.activity)) continue;
        const want = Math.min(+r.minutes, need);
        let { pieces, left } = take(slots, want, U.toMin(r.startTime));
        if (left > 0 && r.startTime) {
          const more = take(slots, left);
          pieces = pieces.concat(more.pieces);
          left = more.left;
        }
        push(pieces, r);
        need -= want - left;
        if (left > 0) res.warnings.push(`no free time left for "${r.name}" (${U.fmtDur(left)} missing)`);
      }

      if (need > 0) {
        const src = remainder || (settings.defaultProject && settings.defaultActivity
          ? { name: 'default', project: settings.defaultProject, activity: settings.defaultActivity,
              projectLabel: settings.defaultProjectLabel, activityLabel: settings.defaultActivityLabel,
              description: settings.defaultDescription }
          : null);
        if (!src) {
          res.warnings.push(`${U.fmtDur(need)} unassigned: set a default project/activity or a remainder rule`);
        } else {
          const { pieces, left } = take(slots, need);
          push(pieces, src);
          if (left > 0) res.warnings.push(`${U.fmtDur(left)} could not be placed (no free slot)`);
        }
      }
      return finish(res);
    });
  }

  function finish(res) {
    res.entries.sort((a, b) => a.start - b.start);
    res.plannedMin = res.entries.reduce((a, e) => a + e.end - e.start, 0);
    res.diff = res.target - res.existingMin - res.plannedMin;
    return res;
  }

  return { plan, ruleApplies, take, subtract };
})();

if (typeof module !== 'undefined') module.exports = Planner;