/*
    _                _      _  ____   _                           _____
   / \    _ __  ___ | |__  (_)/ ___| | |_  ___   __ _  _ __ ___  |  ___|__ _  _ __  _ __ ___
  / _ \  | '__|/ __|| '_ \ | |\___ \ | __|/ _ \ / _` || '_ ` _ \ | |_  / _` || '__|| '_ ` _ \
 / ___ \ | |  | (__ | | | || | ___) || |_|  __/| (_| || | | | | ||  _|| (_| || |   | | | | | |
/_/   \_\|_|   \___||_| |_||_||____/  \__|\___| \__,_||_| |_| |_||_|   \__,_||_|   |_| |_| |_|

 Copyright 2015-2016 Łukasz "JustArchi" Domeradzki
 Contact: JustArchi@JustArchi.net

 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
 You may obtain a copy of the License at

 http://www.apache.org/licenses/LICENSE-2.0
					
 Unless required by applicable law or agreed to in writing, software
 distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.

*/

using System;
using System.Security.Cryptography;
using System.Text;

namespace ArchiSteamFarm {
	internal static class CryptoHelper {
		internal enum ECryptoMethod : byte {
			PlainText,
			AES,
			ProtectedDataForCurrentUser
		}

		private static byte[] EncryptionKey = Encoding.UTF8.GetBytes("ArchiSteamFarm");

		internal static void SetEncryptionKey(string key) {
			if (string.IsNullOrEmpty(key)) {
				Logging.LogNullError(nameof(key));
				return;
			}

			EncryptionKey = Encoding.UTF8.GetBytes(key);
		}

		internal static string Encrypt(ECryptoMethod cryptoMethod, string decrypted) {
			if (string.IsNullOrEmpty(decrypted)) {
				Logging.LogNullError(nameof(decrypted));
				return null;
			}

			switch (cryptoMethod) {
				case ECryptoMethod.PlainText:
					return decrypted;
				case ECryptoMethod.AES:
					return EncryptAES(decrypted);
				case ECryptoMethod.ProtectedDataForCurrentUser:
					return EncryptProtectedDataForCurrentUser(decrypted);
				default:
					return null;
			}
		}

		internal static string Decrypt(ECryptoMethod cryptoMethod, string encrypted) {
			if (string.IsNullOrEmpty(encrypted)) {
				Logging.LogNullError(nameof(encrypted));
				return null;
			}

			switch (cryptoMethod) {
				case ECryptoMethod.PlainText:
					return encrypted;
				case ECryptoMethod.AES:
					return DecryptAES(encrypted);
				case ECryptoMethod.ProtectedDataForCurrentUser:
					return DecryptProtectedDataForCurrentUser(encrypted);
				default:
					return null;
			}
		}

		private static string EncryptAES(string decrypted) {
			if (string.IsNullOrEmpty(decrypted)) {
				Logging.LogNullError(nameof(decrypted));
				return null;
			}

			try {
				byte[] key;
				using (SHA256Cng sha256 = new SHA256Cng()) {
					key = sha256.ComputeHash(EncryptionKey);
				}

				byte[] encryptedData = Encoding.UTF8.GetBytes(decrypted);
				encryptedData = SteamKit2.CryptoHelper.SymmetricEncrypt(encryptedData, key);
				return Convert.ToBase64String(encryptedData);
			} catch (Exception e) {
				Logging.LogGenericException(e);
				return null;
			}
		}

		private static string DecryptAES(string encrypted) {
			if (string.IsNullOrEmpty(encrypted)) {
				Logging.LogNullError(nameof(encrypted));
				return null;
			}

			try {
				byte[] key;
				using (SHA256Cng sha256 = new SHA256Cng()) {
					key = sha256.ComputeHash(EncryptionKey);
				}

				byte[] decryptedData = Convert.FromBase64String(encrypted);
				decryptedData = SteamKit2.CryptoHelper.SymmetricDecrypt(decryptedData, key);
				return Encoding.UTF8.GetString(decryptedData);
			} catch (Exception e) {
				Logging.LogGenericException(e);
				return null;
			}
		}

		private static string EncryptProtectedDataForCurrentUser(string decrypted) {
			if (string.IsNullOrEmpty(decrypted)) {
				Logging.LogNullError(nameof(decrypted));
				return null;
			}

			try {
				byte[] encryptedData = ProtectedData.Protect(
					Encoding.UTF8.GetBytes(decrypted),
					EncryptionKey, // This is used as salt only
					DataProtectionScope.CurrentUser
				);

				return Convert.ToBase64String(encryptedData);
			} catch (Exception e) {
				Logging.LogGenericException(e);
				return null;
			}
		}

		private static string DecryptProtectedDataForCurrentUser(string encrypted) {
			if (string.IsNullOrEmpty(encrypted)) {
				Logging.LogNullError(nameof(encrypted));
				return null;
			}

			try {
				byte[] decryptedData = ProtectedData.Unprotect(
					Convert.FromBase64String(encrypted),
					EncryptionKey, // This is used as salt only
					DataProtectionScope.CurrentUser
				);

				return Encoding.UTF8.GetString(decryptedData);
			} catch (Exception e) {
				Logging.LogGenericException(e);
				return null;
			}
		}
	}
}