Function useSyncLanguageWithPath

src/hooks/useSyncLanguageWithPath.ts:29–115

()

 * - Keeps i18n language aligned with the path locale.
 */
export function useSyncLanguageWithPath() {
  const { i18n } = useTranslation();
  const location = useLocation();
  const navigate = useNavigate();

  useEffect(() => {
    const sp = new URLSearchParams(location.search);

    // 1) Legacy migration: ?lang=fr -> /fr/... (preserve other params)
    const legacyLangRaw = sp.get('lang');
    const legacyLang = legacyLangRaw ? normalizeLang(legacyLangRaw) : undefined;
    if (legacyLangRaw) {
      sp.delete('lang');

      const { restPath } = stripLangPrefix(location.pathname);
      const targetPath = withLangPrefix(restPath, legacyLang ?? 'en');
      navigate(
        {
          pathname: targetPath,
          search: sp.toString(),
          hash: location.hash
        },
        { replace: true }
      );

      if (i18n.language !== (legacyLang ?? 'en')) {
        i18n.changeLanguage(legacyLang ?? 'en');
      }
      return;
    }

    // 2) Ensure we always have a locale prefix.
    // If the user lands on a legacy (no-locale) URL, choose a default based on
    // detected language (navigator/localStorage) instead of always forcing /en/.
    const pathLang = getPathLang(location.pathname);
    if (!pathLang) {
      const detected = normalizeLang(i18n.resolvedLanguage || i18n.language);
      const preferred = detected !== 'en' ? detected : getBrowserPreferredLanguage();

      const targetPath = withLangPrefix(location.pathname || '/', preferred);
      navigate(
        {
          pathname: targetPath,
          search: location.search,
          hash: location.hash
        },
        { replace: true }
      );
      if (i18n.language !== preferred) i18n.changeLanguage(preferred);
      return;
    }

    // 3) Normalize /en -> /en/
    if (location.pathname === `/${pathLang}`) {
      navigate(
        {
          pathname: `/${pathLang}/`,
          search: location.search,