extension UserSessionRepositoryProvider on Ref {
  UserSessionRepository get userSessionRepository => 
      read(userSessionRepositoryProvider);

  UserSessionRepository get userSessionRepository$ => 
      watch(userSessionRepositoryProvider);
}

Future<UserSession> startSession({
  required Session session,
}) async {
  final activeSession = await ref.userSessionRepository
      .getActiveSession(idOrThrow);
  if (activeSession != null) {
    throw AlreadyRunningSessionException();
  }
  return ref.userSessionRepository.start(
    idOrThrow,
    UserSession.fromSession(session),
  );
}

@override
Duration get duration => switch (revenueCatPackage.storeProduct.subscriptionPeriod) {
  'P1W' => const Duration(days: 7),
  'P1M' => const Duration(days: 30),
  'P3M' => const Duration(days: 90),
  'P6M' => const Duration(days: 180),
  'P1Y' => const Duration(days: 365),
  _ => Duration.zero,
};

@override
int? get trialDays {
  final introductory = revenueCatPackage.storeProduct.introductoryPrice;
  if (introductory == null) {
    return null;
  }
  if (introductory.price == 0) {
    final unit = introductory.periodUnit;
    switch (unit) {
      case PeriodUnit.day:
        return introductory.periodNumberOfUnits;
      case PeriodUnit.week:
        return introductory.periodNumberOfUnits * 7;
      case PeriodUnit.month:
        return introductory.periodNumberOfUnits * 30;
      case PeriodUnit.year:
        return introductory.periodNumberOfUnits * 365;
      default:
        return null;
    }
  }
  return null;
}

@override
List<String>? get features {
  final locale = LocaleSettings.currentLocale.languageCode;
  if (revenueCatOffer.metadata[locale] == null) {
    return null;
  }

  final data = revenueCatOffer.metadata[locale]! as Map<Object?, Object?>;
  final featurerObj = data["features"]! as List<Object?>;
  return featurerObj.map((e) => e! as String).toList();
}

class SubscriptionModel extends ChangeNotifier {
  bool _isSubscribed = false;
  DateTime? _expiryDate;

  bool get isSubscribed => _isSubscribed;
  DateTime? get expiryDate => _expiryDate;

  void updateStatus({required bool subscribed, DateTime? expiry}) {
    _isSubscribed = subscribed;
    _expiryDate = expiry;
    notifyListeners();
  }

  void reset() {
    _isSubscribed = false;
    _expiryDate = null;
    notifyListeners();
  }

  bool get isExpired {
    if (_expiryDate == null) return true;
    return DateTime.now().isAfter(_expiryDate!);
  }
}

void main() {
  runApp(
    ChangeNotifierProvider(
      create: (_) => SubscriptionModel(),
      child: const MyApp(),
    ),
  );
}

Consumer<SubscriptionModel>(
  builder: (context, model, _) {
    if (model.isSubscribed) {
      return const PremiumContent();
    }

    return Column(
      children: [
        const Text("Оформите подписку для доступа к премиум-функциям"),
        ElevatedButton(
          onPressed: () => handleSubscription(context),
          child: const Text("Подписаться"),
        ),
      ],
    );
  },
)

Future<void> handleSubscription(BuildContext context) async {
  final model = context.read<SubscriptionModel>();

  final result = await PurchaseService.buy(); // ваша реализация

  if (result.success) {
    model.updateStatus(
      subscribed: true,
      expiry: result.expiryDate,
    );
  } else {
    ScaffoldMessenger.of(context).showSnackBar(
      const SnackBar(content: Text("Не удалось оформить подписку")),
    );
  }
}

class SessionExerciceTitle extends ConsumerStatefulWidget {
  const SessionExerciceTitle({super.key});

  @override
  ConsumerState<ConsumerStatefulWidget> createState() => _SessionExerciceTitleState();
}

class _SessionExerciceTitleState extends ConsumerState<SessionExerciceTitle> {
  Key titleKey(AsyncValue<UserSessionState> state) => 
    ValueKey<String?>("My-${state.value?.currentStepIndex}");

  @override
  Widget build(BuildContext context) {
    final state = ref.watch(userSessionNotifierProvider); // Следим за изменениями состояния
    return AnimatedSwitcher(
      duration: const Duration(milliseconds: 250), // Продолжительность анимации
      switchInCurve: Curves.easeInOut, // Кривая анимации при появлении
      transitionBuilder: (Widget child, Animation<double> animation) {
        // Строитель анимации перехода
        return ScaleTransition(scale: animation, child: child);
      },
      child: Text(
        state.value?.myText ?? '', // Отображаемый текст
        key: titleKey(state), // Ключ, который запускает анимацию при изменении состояния
        textAlign: TextAlign.center, // Выравнивание текста
      ),
    );
  }
}