import 'dart:convert';
import 'dart:math';
import 'dart:typed_data';
import 'package:crypto/crypto.dart';
import 'package:pointycastle/export.dart' as pc;

class CryptoService {
  static const int keySize = 32;
  static const int nonceSize = 24;
  static const int saltSize = 16;

  Uint8List generateKey() {
    final random = Random.secure();
    final key = Uint8List(keySize);
    for (int i = 0; i < keySize; i++) {
      key[i] = random.nextInt(256);
    }
    return key;
  }

  Uint8List generateNonce() {
    final random = Random.secure();
    final nonce = Uint8List(nonceSize);
    for (int i = 0; i < nonceSize; i++) {
      nonce[i] = random.nextInt(256);
    }
    return nonce;
  }

  Uint8List deriveKey(String password, Uint8List salt) {
    final key = pbkdf2(
      hash: sha256,
      password: utf8.encode(password),
      salt: salt,
      iterations: 100000,
      keyLength: keySize,
    );
    return Uint8List.fromList(key);
  }

  Uint8List encrypt(Uint8List plaintext, Uint8List key) {
    final nonce = generateNonce();
    final hmac = Hmac(sha256, key);
    final mac = hmac.convert(plaintext).bytes;

    final result = Uint8List(nonce.length + mac.length + plaintext.length);
    result.setAll(0, nonce);
    result.setAll(nonce.length, mac);
    result.setAll(nonce.length + mac.length, plaintext);

    return result;
  }

  Uint8List? decrypt(Uint8List ciphertext, Uint8List key) {
    try {
      if (ciphertext.length < nonceSize + 32) return null;
      final nonce = ciphertext.sublist(0, nonceSize);
      final mac = ciphertext.sublist(nonceSize, nonceSize + 32);
      final plaintext = ciphertext.sublist(nonceSize + 32);

      final hmac = Hmac(sha256, key);
      final expectedMac = hmac.convert(plaintext).bytes;
      if (!listEquals(mac, expectedMac)) return null;

      return plaintext;
    } catch (_) {
      return null;
    }
  }

  String hashFile(Uint8List data) {
    return sha256.convert(data).toString();
  }

  bool listEquals(List<int> a, List<int> b) {
    if (a.length != b.length) return false;
    for (int i = 0; i < a.length; i++) {
      if (a[i] != b[i]) return false;
    }
    return true;
  }

  Uint8List generateKeyPairSeed() {
    return generateKey();
  }
}