import { format, type Locale } from 'date-fns'
import { toJalaali } from 'jalaali-js'

const JALALI_MONTHS_FA = [
  'فروردین',
  'اردیبهشت',
  'خرداد',
  'تیر',
  'مرداد',
  'شهریور',
  'مهر',
  'آبان',
  'آذر',
  'دی',
  'بهمن',
  'اسفند',
] as const

const PERSIAN_DIGITS = ['۰', '۱', '۲', '۳', '۴', '۵', '۶', '۷', '۸', '۹'] as const

/** Western digits → Persian (Extended Arabic-Indic) numerals, e.g. 1405 → ۱۴۰۵ */
export function toPersianDigits(input: string): string {
  return input.replace(/\d/g, (ch) => PERSIAN_DIGITS[Number(ch)] ?? ch)
}

function pad2(n: number): string {
  return n < 10 ? `0${n}` : `${n}`
}

function formatJalaliAbsolute(date: Date, pattern: string): string {
  const { jy, jm, jd } = toJalaali(date)
  const monthName = JALALI_MONTHS_FA[jm - 1]
  const h = pad2(date.getHours())
  const min = pad2(date.getMinutes())

  let s: string
  switch (pattern) {
    case 'd MMM yyyy':
      s = `${jd} ${monthName} ${jy}`
      break
    case 'd MMM yyyy · HH:mm':
      s = `${jd} ${monthName} ${jy} · ${h}:${min}`
      break
    case 'd MMM yyyy HH:mm':
      s = `${jd} ${monthName} ${jy} ${h}:${min}`
      break
    case 'd MMM · HH:mm':
      s = `${jd} ${monthName} · ${h}:${min}`
      break
    case 'MMM d, yyyy':
      s = `${monthName} ${jd}، ${jy}`
      break
    default:
      s = `${jd} ${monthName} ${jy}`
  }
  return toPersianDigits(s)
}

/**
 * Absolute calendar dates for Persian (`fa`) use the Solar Hijri (Jalali / هجری شمسی) calendar.
 * Times remain in the user's local timezone. For relative phrases, keep using `formatDistanceToNow` with `faIR`.
 */
export function formatAbsoluteDateLocalized(
  date: Date | string,
  language: string,
  pattern: string,
  locale: Locale
): string {
  const d = typeof date === 'string' ? new Date(date) : date
  if (language === 'fa') {
    return formatJalaliAbsolute(d, pattern)
  }
  return format(d, pattern, { locale })
}