import 'dart:convert';
import 'package:login_vault_app/constants.dart';

/// XOR cipher keyed by [AppConstants.encryptionKey], then base64-encoded.
///
/// Operates on raw bytes so any Unicode content round-trips correctly.
class Encryptor {
  static List<int> _xorBytes(List<int> input, List<int> key) {
    final out = List<int>.filled(input.length, 0);
    for (var i = 0; i < input.length; i++) {
      out[i] = input[i] ^ key[i % key.length];
    }
    return out;
  }

  /// Encrypt [plain] -> base64 string using the constant key.
  static String encrypt(String plain) {
    final keyBytes = utf8.encode(AppConstants.encryptionKey);
    final xored = _xorBytes(utf8.encode(plain), keyBytes);
    return base64.encode(xored);
  }

  /// Decrypt a base64 [cipher] produced by [encrypt].
  static String decrypt(String cipher) {
    final keyBytes = utf8.encode(AppConstants.encryptionKey);
    final xored = _xorBytes(base64.decode(cipher), keyBytes);
    return utf8.decode(xored);
  }

  /// Encrypt [plain] with a user password (for backup files).
  /// Uses the password bytes as the XOR key so the backup is protected by the
  /// app password, not the in-app constant key.
  static String encryptWithPassword(String plain, String password) {
    final keyBytes = utf8.encode(password);
    final xored = _xorBytes(utf8.encode(plain), keyBytes);
    return base64.encode(xored);
  }

  /// Decrypt a backup [cipher] produced by [encryptWithPassword].
  static String decryptWithPassword(String cipher, String password) {
    final keyBytes = utf8.encode(password);
    final xored = _xorBytes(base64.decode(cipher), keyBytes);
    return utf8.decode(xored);
  }
}