import { createI18n } from 'vue-i18n'
import { messages, supportedLocales } from './messages'
import type { SupportedLocale } from './messages'

const saved = localStorage.getItem('hermes_locale')

function normalize(tag: string): SupportedLocale {
  return tag.toLowerCase().startsWith('zh') ? 'zh' : 'en'
}

function resolveLocale(saved: string | null): SupportedLocale {
  if (saved && (supportedLocales as readonly string[]).includes(saved)) {
    return saved as SupportedLocale
  }

  // A locale stored before the zh/en-only consolidation (for example 'zh-TW'
  // or 'ja') is no longer supported; remap it instead of dropping to English.
  if (saved) return normalize(saved)

  const preferred = navigator.languages[0]
  return preferred ? normalize(preferred) : 'en'
}

function setHtmlLang(locale: SupportedLocale) {
  document.documentElement.lang = locale
}

const locale = resolveLocale(saved)
setHtmlLang(locale)

export const i18n = createI18n({
  legacy: false,
  locale,
  fallbackLocale: 'en',
  messages,
})

export function switchLocale(newLocale: string): void {
  ;(i18n.global.locale as any).value = newLocale
  setHtmlLang(newLocale as SupportedLocale)
}