import 'dart:math';

import 'package:flutter_secure_storage/flutter_secure_storage.dart';

class LocalVaultService {
  LocalVaultService._();

  static final LocalVaultService instance = LocalVaultService._();

  static const String _encryptionKeyStorageKey =
      'notes_local_encryption_key_v1';

  final FlutterSecureStorage _secureStorage = FlutterSecureStorage();

  String? _cachedEncryptionKey;

  Future<String?> readEncryptionKey() async {
    final String? cachedKey = _cachedEncryptionKey;
    if (cachedKey != null) {
      return cachedKey;
    }

    final String? storedKey = await _secureStorage.read(
      key: _encryptionKeyStorageKey,
    );

    _cachedEncryptionKey = storedKey;
    return storedKey;
  }

  Future<String> createEncryptionKey() async {
    final String encryptionKey = _generateEncryptionKey();

    await _secureStorage.write(
      key: _encryptionKeyStorageKey,
      value: encryptionKey,
    );

    _cachedEncryptionKey = encryptionKey;
    return encryptionKey;
  }

  Future<void> clearEncryptionKey() async {
    await _secureStorage.delete(key: _encryptionKeyStorageKey);
    _cachedEncryptionKey = null;
  }

  String _generateEncryptionKey() {
    final Random random = Random.secure();
    final List<int> bytes = List<int>.generate(32, (_) => random.nextInt(256));

    return bytes
        .map((int byte) => byte.toRadixString(16).padLeft(2, '0'))
        .join();
  }
}