import { KeyPrefix, Namespace, createInstance } from 'i18next'
import resourcesToBackend from 'i18next-resources-to-backend'
import { initReactI18next } from 'react-i18next/initReactI18next'
import { getOptions, languages, fallbackLng } from './settings'
import { cookies, headers } from 'next/headers'
import acceptLanguage from 'accept-language'

const initI18next = async (lng: string, ns: string | string[]) => {
  // on server side we create a new instance for each render, because during compilation everything seems to be executed in parallel
  const i18nInstance = createInstance()
  await i18nInstance
    .use(initReactI18next)
    .use(resourcesToBackend((language: string, namespace: string) => import(`./locales/${language}/${namespace}.json`)))
    .init(getOptions(lng, ns))
  return i18nInstance
}

acceptLanguage.languages(languages)
const cookieName = 'i18next'

export function detectLanguage() {
  const ckies = cookies()
  const hders = headers()
  let lng
  const nextUrlHeader = hders.has('next-url') && hders.get('next-url')
  if (nextUrlHeader && nextUrlHeader.indexOf(`"lng":"`) > -1) {
    const qsObj = JSON.parse(nextUrlHeader.substring(nextUrlHeader.indexOf('{'), nextUrlHeader.indexOf(`}`) + 1))
    lng = qsObj.lng
  }
  if (!lng && ckies.has(cookieName)) lng = acceptLanguage.get(ckies?.get(cookieName)?.value)
  if (!lng) lng = acceptLanguage.get(hders.get('Accept-Language'))
  if (!lng) lng = fallbackLng
  return lng
}

export async function useTranslation<N extends Namespace, TKPrefix extends KeyPrefix<N>>(
  ns: N,
  options: { keyPrefix?: TKPrefix } = {},
) {
  const lng = detectLanguage()
  const i18nextInstance = await initI18next(lng, ns)
  return {
    t: i18nextInstance.getFixedT(lng, Array.isArray(ns) ? ns[0] : ns, options.keyPrefix),
    i18n: i18nextInstance,
  }
}