import type { Language } from 'element-plus/es/locale'
import enLocale from 'element-plus/es/locale/lang/en'

export const LOCALE_MONDAY = 'en-ivy-mon'
export const LOCALE_SUNDAY = 'en-ivy-sun'

type DayjsFactory = typeof import('dayjs')

export const normalizeWeekStart = (weekStart?: number): number => {
  // Sunday is 0 in IvyForms but dayjs/Element Plus expect 7 (EP uses `weekStart || 7`).
  if (weekStart === 0 || weekStart === 7) return 7
  return weekStart ?? 1
}

export const getWeekLocaleName = (weekStart?: number): string => {
  return normalizeWeekStart(weekStart) === 7 ? LOCALE_SUNDAY : LOCALE_MONDAY
}

const ensureWeekLocaleRegistered = (dayjs: DayjsFactory, weekStart?: number): string => {
  const name = getWeekLocaleName(weekStart)
  const weekStartValue = normalizeWeekStart(weekStart) === 7 ? 7 : 1
  const baseLocale = dayjs.Ls.en ?? {}

  if (!dayjs.Ls[name] || (dayjs.Ls[name] as { weekStart?: number }).weekStart !== weekStartValue) {
    dayjs.locale(name, { ...baseLocale, name, weekStart: weekStartValue }, true)
  }

  return name
}

export const createWeekLocaleHelpers = (dayjs: DayjsFactory) => {
  const getWeekLocale = (weekStart?: number): Language => {
    const name = ensureWeekLocaleRegistered(dayjs, weekStart)
    return { ...enLocale, name }
  }

  return { getWeekLocale, getWeekLocaleName }
}