VOZI Premium Mode and Developer Toggle: Access Control

// From PremiumStore
static const String freePhonemeCode = 'R';

bool isFreePhoneme(Phoneme phoneme) => phoneme.code == freePhonemeCode;

bool canAccess(Phoneme phoneme) =>
    _isPremiumEnabled || isFreePhoneme(phoneme);

// Reading from the store in any widget
final premium = PremiumScope.of(context);

if (premium.canAccess(phoneme)) {
  // Show the exercise
} else {
  // Show the locked station UI
}

// Called automatically when auth state changes
void _observeAccount() {
  final client = SupabaseClientProvider.client;
  if (client == null) return;
  _authSub = client.auth.onAuthStateChange.listen((data) {
    if (data.session != null) {
      refreshFromAccount();
    } else {
      _source = PremiumSource.localDemo;
      notifyListeners();
    }
  });
}

class DeveloperStore extends ChangeNotifier {
  static const String _kEnabled = 'vozi_developer_mode_enabled_v1';

  bool _isEnabled = false;
  bool _loaded = false;

  /// `true` when the persisted value has been read from `shared_preferences`.
  bool get isLoaded => _loaded;

  /// `true` if developer mode is active (all content unlocked for demo).
  bool get isEnabled => _isEnabled;

  Future<void> load() async {
    final prefs = await SharedPreferences.getInstance();
    _isEnabled = prefs.getBool(_kEnabled) ?? false;
    _loaded = true;
    notifyListeners();
  }

  Future<void> setEnabled(bool value) async {
    if (_isEnabled == value) return;
    _isEnabled = value;
    notifyListeners();
    final prefs = await SharedPreferences.getInstance();
    await prefs.setBool(_kEnabled, value);
  }

  Future<void> toggle() => setEnabled(!_isEnabled);
}

class PremiumScope extends InheritedNotifier<PremiumStore> {
  const PremiumScope({
    super.key,
    required PremiumStore store,
    required super.child,
  }) : super(notifier: store);

  static PremiumStore of(BuildContext context) {
    final scope = context.dependOnInheritedWidgetOfExactType<PremiumScope>();
    assert(scope?.notifier != null, 'No PremiumScope found in tree.');
    return scope!.notifier!;
  }
}