fin-tracker/app/lib/core/theme/theme_controller.dart

import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:shared_preferences/shared_preferences.dart';

const _prefsKey = 'theme_mode';

final themeModeProvider = NotifierProvider<ThemeModeController, ThemeMode>(
  ThemeModeController.new,
);

/// Persists the chosen [ThemeMode] to this device via `shared_preferences`.
class ThemeModeController extends Notifier<ThemeMode> {
  @override
  ThemeMode build() {
    Future.microtask(_restore);
    return ThemeMode.system;
  }

  Future<void> _restore() async {
    final prefs = await SharedPreferences.getInstance();
    final saved = prefs.getString(_prefsKey);
    state = ThemeMode.values.asNameMap()[saved] ?? ThemeMode.system;
  }

  Future<void> setMode(ThemeMode mode) async {
    state = mode;
    final prefs = await SharedPreferences.getInstance();
    await prefs.setString(_prefsKey, mode.name);
  }
}