/**
 * Picks the interface's language and loads its messages into Lingui's global
 * `i18n`, which the components' `t` and `Trans` read. `main.tsx` calls it once
 * before rendering.
 *
 * @module
 */

import { i18n } from "@lingui/core";
import { isLocale, type Locale } from "../shared/locale.ts";

/**
 * Returns the stored locale, else French for a French browser, else English.
 */
function detectLocale(): Locale {
  const stored = localStorage.getItem("locale");
  if (isLocale(stored)) return stored;
  return navigator.language.startsWith("fr") ? "fr" : "en";
}

/**
 * Loads the messages of `locale`, the detected one by default, then activates
 * it and stores it for the next visit. There is no language switch in the
 * interface yet, so the stored one comes from the browser's language.
 */
export async function loadCatalog(
  locale: Locale = detectLocale(),
): Promise<void> {
  const { messages } = await import(`../locales/${locale}.po`);
  i18n.load(locale, messages);
  i18n.activate(locale);
  localStorage.setItem("locale", locale);
}