import type { Locales } from "$i18n/i18n-types";
import { detectLocale, i18n, locales } from "$i18n/i18n-util";
import { loadAllLocales } from "$i18n/i18n-util.sync";
import type { Handle, RequestEvent } from "@sveltejs/kit";
import { initAcceptLanguageHeaderDetector } from "typesafe-i18n/detectors";

loadAllLocales();
const L = i18n();

export const handle: Handle = async ({ event, resolve }) => {
  const locale = getPreferredLocale(event);
  const LL = L[locale];

  // bind locale and translation functions to current request
  event.locals.locale = locale;
  event.locals.LL = LL;

  // replace html lang attribute with correct language
  return resolve(event, {
    transformPageChunk: ({ html }) => html.replace("%lang%", locale),
  });
};

const getPreferredLocale = ({ request, cookies }: RequestEvent) => {
  const langCookie = cookies.get("lang");
  if (langCookie && locales.indexOf(langCookie as Locales) !== -1)
    return langCookie as Locales;

  // detect the preferred language the user has configured in his browser
  // https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Accept-Language
  const acceptLanguageDetector = initAcceptLanguageHeaderDetector(request);

  return detectLocale(acceptLanguageDetector);
};