import 'package:shared_preferences/shared_preferences.dart';
import '../../../core/constants/app_constants.dart';

/// Token 管理服务
/// 负责 Token 的存储、读取、刷新和清除
class TokenService {
  static TokenService? _instance;
  SharedPreferences? _prefs;

  TokenService();

  factory TokenService.getInstance() {
    _instance ??= TokenService();
    return _instance!;
  }

  Future<SharedPreferences> get _preferences async {
    _prefs ??= await SharedPreferences.getInstance();
    return _prefs!;
  }

  /// 获取 Access Token
  Future<String?> getToken() async {
    final prefs = await _preferences;
    return prefs.getString(AppConstants.tokenKey);
  }

  /// 获取 Refresh Token
  Future<String?> getRefreshToken() async {
    final prefs = await _preferences;
    return prefs.getString(AppConstants.refreshTokenKey);
  }

  /// 保存 Token
  Future<void> saveTokens({
    required String token,
    String? refreshToken,
    int? expiresIn,
  }) async {
    final prefs = await _preferences;
    await prefs.setString(AppConstants.tokenKey, token);
    if (refreshToken != null) {
      await prefs.setString(AppConstants.refreshTokenKey, refreshToken);
    }
    if (expiresIn != null) {
      final expiry = DateTime.now().millisecondsSinceEpoch + expiresIn * 1000;
      await prefs.setInt(AppConstants.tokenExpiryKey, expiry);
    }
  }

  /// 刷新 Token
  Future<bool> refreshToken() async {
    // TODO: 实现实际的 Token 刷新逻辑
    // 使用 refreshToken 调用后端接口获取新的 accessToken
    final refreshTok = await getRefreshToken();
    if (refreshTok == null) return false;

    try {
      // 模拟刷新
      // final response = await DioClient().post('/auth/refresh', data: {'refresh_token': refreshTok});
      // await saveTokens(token: response.data['data']['token'], refreshToken: response.data['data']['refresh_token']);
      return true;
    } catch (e) {
      return false;
    }
  }

  /// 检查 Token 是否过期
  Future<bool> isTokenExpired() async {
    final prefs = await _preferences;
    final expiry = prefs.getInt(AppConstants.tokenExpiryKey);
    if (expiry == null) return true;
    return DateTime.now().millisecondsSinceEpoch > expiry;
  }

  /// 清除所有 Token
  Future<void> clearTokens() async {
    final prefs = await _preferences;
    await prefs.remove(AppConstants.tokenKey);
    await prefs.remove(AppConstants.refreshTokenKey);
    await prefs.remove(AppConstants.tokenExpiryKey);
  }

  /// 是否已登录
  Future<bool> isLoggedIn() async {
    final token = await getToken();
    if (token == null) return false;
    return !(await isTokenExpired());
  }
}