nj/app/lib/features/profile/bloc/settings_bloc.dart

// 设置 BLoC — 主题切换 + 应用设置管理
//
// ChangeNotifier 模式（同 MoodBloc），通过 ListenableBuilder 消费。
// Phase 1: 内存态 + TODO 持久化到 SharedPreferences。

import 'package:flutter/material.dart';

// ===== State =====

/// 设置页面状态
class SettingsState {
  final ThemeMode themeMode;
  final bool isLoading;

  const SettingsState({
    this.themeMode = ThemeMode.system,
    this.isLoading = false,
  });

  SettingsState copyWith({ThemeMode? themeMode, bool? isLoading}) =>
      SettingsState(
        themeMode: themeMode ?? this.themeMode,
        isLoading: isLoading ?? this.isLoading,
      );
}

// ===== BLoC =====

/// 设置管理器 — 全局单例，在 NuanjiApp 中创建
class SettingsBloc extends ChangeNotifier {
  SettingsState _state = const SettingsState();
  SettingsState get state => _state;

  /// 切换主题模式
  void changeTheme(ThemeMode mode) {
    _state = _state.copyWith(themeMode: mode);
    notifyListeners();
    // TODO: 持久化到 SharedPreferences
  }

  /// 循环切换: system → light → dark → system
  void cycleTheme() {
    final next = switch (_state.themeMode) {
      ThemeMode.system => ThemeMode.light,
      ThemeMode.light => ThemeMode.dark,
      ThemeMode.dark => ThemeMode.system,
    };
    changeTheme(next);
  }
}