sxchnge/frontend/app/lib/providers/locale.dart

import 'package:flutter/material.dart';

import 'package:shared_preferences/shared_preferences.dart';

class LocaleProvider extends ChangeNotifier {
  static const storageKey = 'sxchnge_last_locale';
  LocaleProvider({Locale initialLocale = const Locale('en'), this.preferences})
    : _locale = resolve(initialLocale.languageCode, const []);

  Locale _locale;
  final SharedPreferences? preferences;
  Future<bool> _pendingSave = Future.value(true);
  Locale get locale => _locale;

  static Locale resolve(String? saved, List<Locale> systemLocales) {
    final code =
        saved?.split(RegExp('[-_]')).first ??
        (systemLocales.isEmpty ? 'en' : systemLocales.first.languageCode);
    return Locale(code == 'ru' ? 'ru' : 'en');
  }

  static Future<LocaleProvider> load(List<Locale> systemLocales) async {
    try {
      final prefs = await SharedPreferences.getInstance();
      return LocaleProvider(
        initialLocale: resolve(prefs.getString(storageKey), systemLocales),
        preferences: prefs,
      );
    } catch (_) {
      return LocaleProvider(initialLocale: resolve(null, systemLocales));
    }
  }

  Future<bool> setLocale(Locale value) {
    final next = resolve(value.languageCode, const []);
    if (next == _locale) return _pendingSave;
    _locale = next;
    notifyListeners();
    // Serialize writes so rapid language changes persist the last selection.
    _pendingSave = _pendingSave.then((_) async {
      try {
        return await preferences?.setString(storageKey, next.languageCode) ??
            false;
      } catch (_) {
        return false;
      }
    });
    return _pendingSave;
  }
}