/** کلید روز (YYYY-MM-DD) و زمان‌ها همگی به وقت تهران (بدون ساعت تابستانی، +03:30). */
export const TEHRAN_OFFSET = '+03:30';

const DAY_FMT = new Intl.DateTimeFormat('en-CA', {
  timeZone: 'Asia/Tehran',
  year: 'numeric',
  month: '2-digit',
  day: '2-digit',
});

const HOUR_FMT = new Intl.DateTimeFormat('en-US', {
  timeZone: 'Asia/Tehran',
  hour: '2-digit',
  hourCycle: 'h23',
});

const JALALI_DAY_FMT = new Intl.DateTimeFormat('en-US-u-ca-persian', {
  timeZone: 'UTC',
  day: 'numeric',
});

const DAY_KEY_RE = /^\d{4}-\d{2}-\d{2}$/;
const TIME_RE = /^([01]\d|2[0-3]):[0-5]\d$/;

export function isDayKey(value: unknown): value is string {
  return typeof value === 'string' && DAY_KEY_RE.test(value);
}

export function isTimeOfDay(value: unknown): value is string {
  return typeof value === 'string' && TIME_RE.test(value);
}

export function tehranDayKey(d: Date = new Date()): string {
  return DAY_FMT.format(d);
}

export function tehranHour(d: Date = new Date()): number {
  return Number(HOUR_FMT.format(d)) % 24;
}

/** مقدار مناسب برای ستون‌های @db.Date */
export function dayKeyToDate(key: string): Date {
  return new Date(`${key}T00:00:00.000Z`);
}

/** خواندن ستون‌های @db.Date */
export function dateToDayKey(d: Date): string {
  return d.toISOString().slice(0, 10);
}

export function addDays(key: string, n: number): string {
  const d = dayKeyToDate(key);
  d.setUTCDate(d.getUTCDate() + n);
  return dateToDayKey(d);
}

/** b - a بر حسب روز */
export function dayDiff(a: string, b: string): number {
  return Math.round(
    (dayKeyToDate(b).getTime() - dayKeyToDate(a).getTime()) / 86_400_000,
  );
}

/** ۰ = شنبه … ۶ = جمعه */
export function persianWeekday(key: string): number {
  return (dayKeyToDate(key).getUTCDay() + 1) % 7;
}

/** شنبهٔ همان هفته */
export function weekStartKey(key: string): string {
  return addDays(key, -persianWeekday(key));
}

export function jalaliDayOfMonth(key: string): number {
  return Number(JALALI_DAY_FMT.format(dayKeyToDate(key)));
}

export function tehranDateTime(key: string, hhmm: string): Date {
  return new Date(`${key}T${hhmm}:00${TEHRAN_OFFSET}`);
}

export function tehranDayStart(key: string): Date {
  return tehranDateTime(key, '00:00');
}

export function eachDay(from: string, to: string): string[] {
  const out: string[] = [];
  let cur = from;
  let guard = 0;
  while (cur <= to && guard < 800) {
    out.push(cur);
    cur = addDays(cur, 1);
    guard += 1;
  }
  return out;
}

export function toFaDigits(value: number | string): string {
  return String(value).replace(/\d/g, (d) => '۰۱۲۳۴۵۶۷۸۹'[Number(d)]!);
}