import 'package:flutter_appauth/flutter_appauth.dart';
import 'package:riverpod_annotation/riverpod_annotation.dart';

import '../config/app_config.dart';

part 'oidc_service.g.dart';

/// OIDC token response containing access and refresh tokens.
class OidcTokens {
  const OidcTokens({
    required this.accessToken,
    required this.refreshToken,
    required this.expiresAt,
    this.idToken,
  });

  final String accessToken;
  final String? refreshToken;
  final DateTime expiresAt;
  final String? idToken;
}

/// Service for OIDC authentication using flutter_appauth.
///
/// Handles the Authorization Code flow with PKCE for secure authentication
/// against Authentik.
class OidcService {
  OidcService({FlutterAppAuth? appAuth}) : _appAuth = appAuth ?? const FlutterAppAuth();

  final FlutterAppAuth _appAuth;

  /// OIDC scopes to request.
  static const _scopes = ['openid', 'profile', 'email', 'offline_access'];

  /// Redirect URI for the app.
  static String get _redirectUri => '${AppConfig.authRedirectScheme}://callback';

  /// Start the authorization code flow.
  ///
  /// Opens a browser/webview for user to authenticate with Authentik,
  /// then exchanges the authorization code for tokens.
  ///
  /// Throws [OidcException] if authentication fails.
  Future<OidcTokens> signIn() async {
    try {
      final result = await _appAuth.authorizeAndExchangeCode(
        AuthorizationTokenRequest(
          AppConfig.authClientId,
          _redirectUri,
          discoveryUrl: AppConfig.authDiscoveryUrl,
          scopes: _scopes,
        ),
      );

      if (result.accessToken == null) {
        throw OidcException('Authorization failed: no access token');
      }

      return OidcTokens(
        accessToken: result.accessToken!,
        refreshToken: result.refreshToken,
        expiresAt: result.accessTokenExpirationDateTime ?? DateTime.now().add(const Duration(hours: 1)),
        idToken: result.idToken,
      );
    } on Exception catch (e) {
      throw OidcException('Authorization failed: $e');
    }
  }

  /// Refresh the access token using a refresh token.
  ///
  /// Throws [OidcException] if refresh fails.
  Future<OidcTokens> refreshToken(String refreshToken) async {
    try {
      final result = await _appAuth.token(
        TokenRequest(
          AppConfig.authClientId,
          _redirectUri,
          discoveryUrl: AppConfig.authDiscoveryUrl,
          refreshToken: refreshToken,
          scopes: _scopes,
        ),
      );

      if (result.accessToken == null) {
        throw OidcException('Token refresh failed: no access token');
      }

      return OidcTokens(
        accessToken: result.accessToken!,
        refreshToken: result.refreshToken ?? refreshToken,
        expiresAt: result.accessTokenExpirationDateTime ?? DateTime.now().add(const Duration(hours: 1)),
        idToken: result.idToken,
      );
    } on Exception catch (e) {
      throw OidcException('Token refresh failed: $e');
    }
  }
}

/// Exception thrown when OIDC operations fail.
class OidcException implements Exception {
  const OidcException(this.message);

  final String message;

  @override
  String toString() => 'OidcException: $message';
}

/// Provider for the OIDC service.
@riverpod
OidcService oidcService(Ref ref) {
  return OidcService();
}