import { createInstance } from 'i18next'
import { initReactI18next } from 'react-i18next'

import ainuNavigation from '@/locales/ain-Kana/navigation.json'
import ainuCommon from '@/locales/ain-Kana/common.json'
import ainuTags from '@/locales/ain-Kana/tags.json'
import nipponeseNavigation from '@/locales/ja/navigation.json'
import nipponeseCommon from '@/locales/ja/common.json'
import nipponeseTags from '@/locales/ja/tags.json'

import type { LocaleCode } from '@/lib/locales'

export const i18n = createInstance ()


// Keep Japanese placeholders editable without reporting them as completed translations.
const translatedResource = (resource: Record<string, unknown>): Record<string, unknown> => {
  const untranslated = new Set (
      Array.isArray (resource._untranslated) ? resource._untranslated : [])
  const select = (entries: Record<string, unknown>, prefix = ''): Record<string, unknown> =>
      Object.fromEntries (Object.entries (entries).flatMap (([key, value]) => {
	const path = prefix ? `${ prefix }.${ key }` : key
	if (key === '_untranslated' || untranslated.has (path))
	  return []
	const translated =
	    (value != null && typeof value === 'object' && !(Array.isArray (value)))
	    ? select (value as Record<string, unknown>, path)
	    : value
	return [[key, translated]]
      }))
  return select (resource)
}


void i18n.use (initReactI18next).init ({
    lng: 'ja',
    fallbackLng: 'ja',
    supportedLngs: ['ja', 'ain-Kana'],
    load: 'currentOnly',
    initAsync: false,
    defaultNS: 'navigation',
    ns: ['navigation', 'common', 'tags'],
    resources: {
	ja: { navigation: nipponeseNavigation, common: nipponeseCommon, tags: nipponeseTags },
	'ain-Kana': {
	    navigation: ainuNavigation,
	    common: translatedResource (ainuCommon),
	    tags: translatedResource (ainuTags) } },
    interpolation: { escapeValue: false },
    returnNull: false,
    returnEmptyString: false,
    saveMissing: import.meta.env.DEV,
    missingKeyHandler: (languages, namespace, key) => {
      console.warn ('[i18n] missing key', { languages, namespace, key })
    },
    react: { useSuspense: false } })


export const untranslatedKeys = (
    locale: LocaleCode,
    namespace = 'navigation',
): string[] => {
  const collect = (resource: Record<string, unknown>, prefix = ''): string[] =>
      Object.entries (resource).flatMap (([key, value]) => {
	const path = prefix ? `${ prefix }.${ key }` : key
	return (value != null && typeof value === 'object')
	    ? collect (value as Record<string, unknown>, path)
	    : [path]
      })
  const baseline = i18n.getResourceBundle ('ja', namespace) ?? { }
  return collect (baseline).filter (key => {
    const value = i18n.getResource (locale, namespace, key)
    return typeof value !== 'string' || value.length === 0
  })
}


if (import.meta.env.DEV)
{
  for (const namespace of ['navigation', 'common', 'tags'])
  {
    const missing = untranslatedKeys ('ain-Kana', namespace)
    if (missing.length > 0)
      console.warn (`[i18n] ain-Kana: untranslated ${ namespace } keys`, missing)
  }
}