import { jalaaliMonthLength, toGregorian, toJalaali } from 'jalaali-js'

const persianDigits = '۰۱۲۳۴۵۶۷۸۹'

function toPersianDigits(input: string): string {
  return input.replace(/\d/g, (d) => persianDigits[Number(d)]!)
}

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

export const JALALI_WEEKDAY_NAMES = ['ش', 'ی', 'د', 'س', 'چ', 'پ', 'ج'] as const

export interface JalaliDate {
  jy: number
  jm: number
  jd: number
}

export function parseISODate(iso: string): Date {
  const match = iso.trim().match(/^(\d{4})-(\d{2})-(\d{2})/)
  if (match) {
    return new Date(Number(match[1]), Number(match[2]) - 1, Number(match[3]))
  }

  const parsed = new Date(iso)
  if (Number.isNaN(parsed.getTime())) {
    return new Date(NaN)
  }

  return new Date(parsed.getFullYear(), parsed.getMonth(), parsed.getDate())
}

export function toISODate(date: Date): string {
  const year = date.getFullYear()
  const month = String(date.getMonth() + 1).padStart(2, '0')
  const day = String(date.getDate()).padStart(2, '0')
  return `${year}-${month}-${day}`
}

export function toJalali(date: Date): JalaliDate {
  const { jy, jm, jd } = toJalaali(date.getFullYear(), date.getMonth() + 1, date.getDate())
  return { jy, jm, jd }
}

export function fromJalali(jy: number, jm: number, jd: number): Date {
  const { gy, gm, gd } = toGregorian(jy, jm, jd)
  return new Date(gy, gm - 1, gd)
}

export function isoToJalali(iso: string): JalaliDate | null {
  if (!iso) return null
  return toJalali(parseISODate(iso))
}

export function jalaliToISO(jy: number, jm: number, jd: number): string {
  return toISODate(fromJalali(jy, jm, jd))
}

export function formatJalaliDate(jy: number, jm: number, jd: number): string {
  const month = String(jm).padStart(2, '0')
  const day = String(jd).padStart(2, '0')
  return toPersianDigits(`${jy}/${month}/${day}`)
}

export function formatJalaliLabel(jy: number, jm: number, jd: number): string {
  return `${toPersianDigits(String(jd))} ${JALALI_MONTH_NAMES[jm - 1]} ${toPersianDigits(String(jy))}`
}

export function getPersianWeekday(jy: number, jm: number, jd: number): number {
  const { gy, gm, gd } = toGregorian(jy, jm, jd)
  const jsDay = new Date(gy, gm - 1, gd).getDay()
  return (jsDay + 1) % 7
}

export function getMonthLength(jy: number, jm: number): number {
  return jalaaliMonthLength(jy, jm)
}

export function buildCalendarDays(jy: number, jm: number): Array<number | null> {
  const length = getMonthLength(jy, jm)
  const startWeekday = getPersianWeekday(jy, jm, 1)
  const cells: Array<number | null> = Array.from({ length: startWeekday }, () => null)

  for (let day = 1; day <= length; day += 1) {
    cells.push(day)
  }

  while (cells.length % 7 !== 0) {
    cells.push(null)
  }

  return cells
}

export function todayJalali(): JalaliDate {
  return toJalali(new Date())
}