import 'dart:convert';
import 'dart:math';

import 'package:crypto/crypto.dart';
import 'package:injectable/injectable.dart';
import 'package:isar/isar.dart';
import 'package:mnemo_cards_backend/main.dart' as main;
import 'package:mnemo_cards_common_backend/mnemo_cards_common_backend.dart';

/// Service for JWT token generation and verification
///
/// Generates access tokens (short-lived) and refresh tokens (long-lived)
@lazySingleton
class JwtService {
  // In production, use environment variables or secure key management
  static const String _secretKey = 'your-secret-key-change-in-production';
  static const int _accessTokenExpirySeconds = 3600; // 1 hour
  static const int _refreshTokenExpirySeconds = 2592000; // 30 days

  JwtService();

  /// Generate access and refresh tokens for a user
  Future<JwtTokens> generateTokens(UserModel user) async {
    final now = DateTime.now();
    final jti = _generateJti();

    // Access token payload
    final accessTokenPayload = {
      'sub': user.id.toString(),
      'iat': now.millisecondsSinceEpoch ~/ 1000,
      'exp': (now.millisecondsSinceEpoch ~/ 1000) + _accessTokenExpirySeconds,
      'type': 'access',
      'userId': user.id,
    };

    // Refresh token payload
    final refreshTokenPayload = {
      'sub': user.id.toString(),
      'iat': now.millisecondsSinceEpoch ~/ 1000,
      'exp': (now.millisecondsSinceEpoch ~/ 1000) + _refreshTokenExpirySeconds,
      'type': 'refresh',
      'userId': user.id,
      'jti': jti, // JWT ID for token invalidation
    };

    // Create JWT tokens with proper HMAC-SHA256 signing
    final accessToken = _createSimpleJwt(accessTokenPayload);
    final refreshToken = _createSimpleJwt(refreshTokenPayload);

    // Store refresh token for invalidation
    final userId = user.id;
    if (userId == null) {
      throw Exception('Cannot create tokens for user without ID');
    }
    final expiresAt = now.add(Duration(seconds: _refreshTokenExpirySeconds));
    await _storeRefreshToken(jti, userId, now, expiresAt);

    return JwtTokens(
      accessToken: accessToken,
      refreshToken: refreshToken,
      expiresIn: _accessTokenExpirySeconds,
    );
  }

  /// Verify access token and return user ID
  String? verifyAccessToken(String token) {
    try {
      final payload = _verifySimpleJwt(token);
      if (payload == null) return null;

      // Check if token is expired
      final exp = payload['exp'] as int?;
      if (exp != null) {
        final expiryTime = DateTime.fromMillisecondsSinceEpoch(exp * 1000);
        if (DateTime.now().isAfter(expiryTime)) {
          return null;
        }
      }

      // Check token type
      if (payload['type'] != 'access') {
        return null;
      }

      return payload['userId']?.toString();
    } catch (e) {
      return null;
    }
  }

  /// Verify refresh token and return user ID
  Future<String?> verifyRefreshToken(String token) async {
    try {
      final payload = _verifySimpleJwt(token);
      if (payload == null) return null;

      // Check if token is expired
      final exp = payload['exp'] as int?;
      if (exp != null) {
        final expiryTime = DateTime.fromMillisecondsSinceEpoch(exp * 1000);
        if (DateTime.now().isAfter(expiryTime)) {
          return null;
        }
      }

      // Check token type
      if (payload['type'] != 'refresh') {
        return null;
      }

      // Check if token is blacklisted
      final jti = payload['jti'] as String?;
      if (jti != null) {
        final isBlacklisted = await _isTokenBlacklisted(jti);
        if (isBlacklisted) {
          return null;
        }
      }

      return payload['userId']?.toString();
    } catch (e) {
      return null;
    }
  }

  /// Create a simple JWT (base64 encoded JSON)
  /// Note: This is a simplified implementation
  /// For production, use a proper JWT library with proper signing
  String _createSimpleJwt(Map<String, dynamic> payload) {
    final header = {'alg': 'HS256', 'typ': 'JWT'};
    final headerB64 = base64UrlEncode(utf8.encode(jsonEncode(header)));
    final payloadB64 = base64UrlEncode(utf8.encode(jsonEncode(payload)));

    // Create signature (simplified - in production use proper HMAC)
    final signatureInput = '$headerB64.$payloadB64';
    final signature = _hmacSha256(utf8.encode(signatureInput), _secretKey);
    final signatureB64 = base64UrlEncode(signature);

    return '$headerB64.$payloadB64.$signatureB64';
  }

  /// Verify a simple JWT
  Map<String, dynamic>? _verifySimpleJwt(String token) {
    try {
      final parts = token.split('.');
      if (parts.length != 3) return null;

      final headerB64 = parts[0];
      final payloadB64 = parts[1];
      final signatureB64 = parts[2];

      // Verify signature
      final signatureInput = '$headerB64.$payloadB64';
      final expectedSignature =
          _hmacSha256(utf8.encode(signatureInput), _secretKey);
      final expectedSignatureB64 = base64UrlEncode(expectedSignature);

      if (signatureB64 != expectedSignatureB64) {
        return null; // Invalid signature
      }

      // Decode payload
      final payloadJson = utf8.decode(base64Url.decode(payloadB64));
      return jsonDecode(payloadJson) as Map<String, dynamic>;
    } catch (e) {
      return null;
    }
  }

  /// Extract payload from JWT without verification (for extracting jti during logout)
  Map<String, dynamic>? extractPayload(String token) {
    try {
      final parts = token.split('.');
      if (parts.length != 3) return null;

      final payloadB64 = parts[1];
      final payloadJson = utf8.decode(base64Url.decode(payloadB64));
      return jsonDecode(payloadJson) as Map<String, dynamic>;
    } catch (e) {
      return null;
    }
  }

  /// HMAC-SHA256 implementation using crypto package
  List<int> _hmacSha256(List<int> data, String key) {
    final keyBytes = utf8.encode(key);
    final hmac = Hmac(sha256, keyBytes);
    final digest = hmac.convert(data);
    return digest.bytes;
  }

  String _generateJti() {
    final random = Random();
    return base64UrlEncode(
      List<int>.generate(16, (_) => random.nextInt(256)),
    );
  }

  Future<void> _storeRefreshToken(
    String jti,
    int userId,
    DateTime createdAt,
    DateTime expiresAt,
  ) async {
    await main.isar.writeTxn(() async {
      // Delete old token if exists (shouldn't happen due to unique index, but be safe)
      final existing = await main.isar.refreshTokenModels
          .filter()
          .jtiEqualTo(jti)
          .findFirst();
      if (existing != null) {
        await main.isar.refreshTokenModels.delete(existing.id!);
      }

      // Store new token
      await main.isar.refreshTokenModels.put(
        RefreshTokenModel(
          jti: jti,
          userId: userId,
          createdAt: createdAt,
          expiresAt: expiresAt,
          isBlacklisted: false,
        ),
      );
    });
  }

  Future<bool> _isTokenBlacklisted(String jti) async {
    final token =
        await main.isar.refreshTokenModels.filter().jtiEqualTo(jti).findFirst();

    if (token == null) {
      return true; // Token not found, consider it invalid
    }

    // Check if expired
    if (token.expiresAt.isBefore(DateTime.now())) {
      return true; // Expired tokens are considered invalid
    }

    return token.isBlacklisted;
  }

  /// Blacklist a refresh token (for logout)
  Future<void> blacklistRefreshToken(String jti) async {
    await main.isar.writeTxn(() async {
      final token = await main.isar.refreshTokenModels
          .filter()
          .jtiEqualTo(jti)
          .findFirst();
      if (token != null) {
        await main.isar.refreshTokenModels.put(
          token.copyWith(isBlacklisted: true),
        );
      }
    });
  }

  /// Clean up expired tokens (should be called periodically)
  Future<void> cleanupExpiredTokens() async {
    await main.isar.writeTxn(() async {
      final now = DateTime.now();
      final expired = await main.isar.refreshTokenModels
          .filter()
          .expiresAtLessThan(now)
          .findAll();
      if (expired.isNotEmpty) {
        final ids = expired
            .map((t) => t.id)
            .where((id) => id != null)
            .cast<Id>()
            .toList();
        if (ids.isNotEmpty) {
          await main.isar.refreshTokenModels.deleteAll(ids);
        }
      }
    });
  }
}

/// JWT tokens result
class JwtTokens {
  final String accessToken;
  final String refreshToken;
  final int expiresIn; // seconds

  JwtTokens({
    required this.accessToken,
    required this.refreshToken,
    required this.expiresIn,
  });
}