sure/mobile/lib/providers/theme_provider.dart

import 'package:flutter/material.dart';
import '../services/preferences_service.dart';

class ThemeProvider extends ChangeNotifier {
  ThemeMode _themeMode = ThemeMode.system;

  ThemeMode get themeMode => _themeMode;

  ThemeProvider() {
    _loadThemeMode();
  }

  Future<void> _loadThemeMode() async {
    try {
      final mode = await PreferencesService.instance.getThemeMode();
      _themeMode = _fromString(mode);
    } catch (_) {
      _themeMode = ThemeMode.system;
    }
    notifyListeners();
  }

  Future<void> setThemeMode(ThemeMode mode) async {
    _themeMode = mode;
    notifyListeners();
    await PreferencesService.instance.setThemeMode(_toString(mode));
  }

  static ThemeMode _fromString(String mode) {
    switch (mode) {
      case 'light':
        return ThemeMode.light;
      case 'dark':
        return ThemeMode.dark;
      default:
        return ThemeMode.system;
    }
  }

  static String _toString(ThemeMode mode) {
    switch (mode) {
      case ThemeMode.light:
        return 'light';
      case ThemeMode.dark:
        return 'dark';
      case ThemeMode.system:
        return 'system';
    }
  }
}