import 'package:flutter/cupertino.dart';
import 'package:shared_preferences/shared_preferences.dart';

enum ThemePreference {
  system,
  light,
  dark;

  static ThemePreference parse(String? raw) {
    return switch (raw) {
      'light' => ThemePreference.light,
      'dark' => ThemePreference.dark,
      _ => ThemePreference.system,
    };
  }

  Brightness resolve(Brightness platform) => switch (this) {
        ThemePreference.system => platform,
        ThemePreference.light => Brightness.light,
        ThemePreference.dark => Brightness.dark,
      };
}

abstract interface class ThemePreferenceStore {
  Future<String?> read();
  Future<void> write(String value);
}

class PrefsThemeStore implements ThemePreferenceStore {
  const PrefsThemeStore();

  static const key = 'ppm_theme_preference';

  @override
  Future<String?> read() async {
    final prefs = await SharedPreferences.getInstance();
    return prefs.getString(key);
  }

  @override
  Future<void> write(String value) async {
    final prefs = await SharedPreferences.getInstance();
    await prefs.setString(key, value);
  }
}

class MemoryThemeStore implements ThemePreferenceStore {
  MemoryThemeStore([this.value]);

  String? value;

  @override
  Future<String?> read() async => value;

  @override
  Future<void> write(String next) async => value = next;
}

/// Survives logout: appearance is a device preference, not a session one.
class ThemeController extends ChangeNotifier {
  ThemeController({ThemePreferenceStore? store}) : _store = store ?? const PrefsThemeStore();

  final ThemePreferenceStore _store;
  ThemePreference _preference = ThemePreference.system;

  ThemePreference get preference => _preference;

  Brightness resolve(Brightness platform) => _preference.resolve(platform);

  Future<void> restore() async {
    _preference = ThemePreference.parse(await _store.read());
    notifyListeners();
  }

  Future<void> setPreference(ThemePreference value) async {
    if (_preference == value) return;
    _preference = value;
    notifyListeners();
    await _store.write(value.name);
  }
}