import type { RoutineRecurrence } from '@mento/shared';
import { ROUTINE_WEEKDAY_LABELS } from '@mento/shared';
import {
  addDays,
  dayDiff,
  jalaliDayOfMonth,
  persianWeekday,
  toFaDigits,
  weekStartKey,
} from './routine-dates';

export type RecurrenceRule = {
  recurrence: RoutineRecurrence;
  startDate: string;
  endDate: string | null;
  weekdays: number[];
  intervalDays: number | null;
  monthDay: number | null;
  specificDates: string[];
};

function weeklyDays(rule: RecurrenceRule): number[] {
  return rule.weekdays.length ? rule.weekdays : [persianWeekday(rule.startDate)];
}

export function occursOn(rule: RecurrenceRule, day: string): boolean {
  if (day < rule.startDate) return false;
  if (rule.endDate && day > rule.endDate) return false;

  switch (rule.recurrence) {
    case 'daily':
      return true;
    case 'weekdays':
    case 'weekly':
      return weeklyDays(rule).includes(persianWeekday(day));
    case 'biweekly': {
      if (!weeklyDays(rule).includes(persianWeekday(day))) return false;
      const weeks = Math.floor(
        dayDiff(weekStartKey(rule.startDate), weekStartKey(day)) / 7,
      );
      return weeks % 2 === 0;
    }
    case 'monthly': {
      const target = rule.monthDay ?? jalaliDayOfMonth(rule.startDate);
      const current = jalaliDayOfMonth(day);
      if (current === target) return true;
      // ماه‌هایی که روز هدف را ندارند (مثلاً ۳۱ در مهر): آخرین روز ماه
      const isLastDay = jalaliDayOfMonth(addDays(day, 1)) === 1;
      return isLastDay && target > current;
    }
    case 'every_n_days': {
      const n = Math.max(1, rule.intervalDays ?? 1);
      return dayDiff(rule.startDate, day) % n === 0;
    }
    case 'specific_dates':
      return rule.specificDates.includes(day);
    default:
      return false;
  }
}

function joinFa(items: string[]): string {
  if (items.length <= 1) return items.join('');
  return `${items.slice(0, -1).join('، ')} و ${items[items.length - 1]}`;
}

function describeWeekdays(days: number[]): string {
  const sorted = [...new Set(days)].sort((a, b) => a - b);
  if (sorted.length === 7) return 'هر روز';
  const contiguous =
    sorted.length >= 3 &&
    sorted.every((d, i) => i === 0 || d === sorted[i - 1]! + 1);
  if (contiguous) {
    return `${ROUTINE_WEEKDAY_LABELS[sorted[0]!]} تا ${ROUTINE_WEEKDAY_LABELS[sorted[sorted.length - 1]!]}`;
  }
  return `هر ${joinFa(sorted.map((d) => ROUTINE_WEEKDAY_LABELS[d]!))}`;
}

export function describeRecurrence(rule: RecurrenceRule): string {
  switch (rule.recurrence) {
    case 'daily':
      return 'هر روز';
    case 'weekdays':
    case 'weekly':
      return describeWeekdays(weeklyDays(rule));
    case 'biweekly':
      return `هر دو هفته، ${joinFa(weeklyDays(rule).map((d) => ROUTINE_WEEKDAY_LABELS[d]!))}`;
    case 'monthly': {
      const day = rule.monthDay ?? jalaliDayOfMonth(rule.startDate);
      return day === 1 ? 'اول هر ماه' : `روز ${toFaDigits(day)} هر ماه`;
    }
    case 'every_n_days': {
      const n = Math.max(1, rule.intervalDays ?? 1);
      return n === 1 ? 'هر روز' : `هر ${toFaDigits(n)} روز یک‌بار`;
    }
    case 'specific_dates':
      return `${toFaDigits(rule.specificDates.length)} تاریخ مشخص`;
    default:
      return '';
  }
}