import { toFaDigits } from '@/utils/persian'
import { toJalaali } from '@/utils/date-utils'

const WEEKDAY_NAMES = ['شنبه', 'یکشنبه', 'دوشنبه', 'سه شنبه', 'چهارشنبه', 'پنجشنبه', 'جمعه']
const MONTH_NAMES = [
  'فروردین',
  'اردیبهشت',
  'خرداد',
  'تیر',
  'مرداد',
  'شهریور',
  'مهر',
  'آبان',
  'آذر',
  'دی',
  'بهمن',
  'اسفند',
]
const GREGORIAN_WEEKDAYS = ['Sat', 'Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri']
const DAY_MS = 24 * 60 * 60 * 1000

/**
 * Builds the current Jalaali week (Saturday → Friday) anchored to the Asia/Tehran
 * timezone, independent of the viewer's local clock. The day matching Tehran's
 * "today" is flagged `selected`. Returns `{ month, days }` for DashboardCalendar.
 */
export const useTehranCalendar = () => {
  const parts = new Intl.DateTimeFormat('en-US', {
    timeZone: 'Asia/Tehran',
    year: 'numeric',
    month: 'numeric',
    day: 'numeric',
    weekday: 'short',
  }).formatToParts(new Date())
  const part = (type) => parts.find((p) => p.type === type)?.value
  const todayIndex = GREGORIAN_WEEKDAYS.indexOf(part('weekday'))
  const todayUtc = Date.UTC(Number(part('year')), Number(part('month')) - 1, Number(part('day')))
  const weekStartUtc = todayUtc - todayIndex * DAY_MS

  const today = new Date(todayUtc)
  const { jm } = toJalaali(today.getUTCFullYear(), today.getUTCMonth() + 1, today.getUTCDate())

  const days = WEEKDAY_NAMES.map((weekday, i) => {
    const date = new Date(weekStartUtc + i * DAY_MS)
    const { jd } = toJalaali(date.getUTCFullYear(), date.getUTCMonth() + 1, date.getUTCDate())
    return { weekday, day: toFaDigits(jd), selected: i === todayIndex }
  })

  return { month: `${MONTH_NAMES[jm - 1]} ماه`, days }
}