// Copyright (c) Pixel Crushers. All rights reserved.

using UnityEngine;
#if UNITY_EDITOR || UNITY_STANDALONE
using System;
using System.Text;
using System.IO;
using System.Security.Cryptography;
#endif

namespace PixelCrushers
{

    public class EncryptionUtility
    {

#if UNITY_EDITOR || UNITY_STANDALONE

        // From: https://developingsoftware.com/how-to-securely-store-data-in-unity-player-preferences

        const int Iterations = 1000;

        public static string Encrypt(string plainText, string password)
        {
            if (string.IsNullOrEmpty(plainText) || string.IsNullOrEmpty(password)) return string.Empty;

            // create instance of the DES crypto provider
            var des = new DESCryptoServiceProvider();

            // generate a random IV will be used a salt value for generating key
            des.GenerateIV();

            // use derive bytes to generate a key from the password and IV
            var rfc2898DeriveBytes = new Rfc2898DeriveBytes(password, des.IV, Iterations);

            // generate a key from the password provided
            byte[] key = rfc2898DeriveBytes.GetBytes(8);

            // encrypt the plainText
            using (var memoryStream = new MemoryStream())
            using (var cryptoStream = new CryptoStream(memoryStream, des.CreateEncryptor(key, des.IV), CryptoStreamMode.Write))
            {
                // write the salt first not encrypted
                memoryStream.Write(des.IV, 0, des.IV.Length);

                // convert the plain text string into a byte array
                byte[] bytes = Encoding.UTF8.GetBytes(plainText);

                // write the bytes into the crypto stream so that they are encrypted bytes
                cryptoStream.Write(bytes, 0, bytes.Length);
                cryptoStream.FlushFinalBlock();

                return Convert.ToBase64String(memoryStream.ToArray());
            }
        }

        public static bool TryDecrypt(string cipherText, string password, out string plainText)
        {
            // its pointless trying to decrypt if the cipher text
            // or password has not been supplied
            if (string.IsNullOrEmpty(cipherText) ||
                string.IsNullOrEmpty(password))
            {
                plainText = string.Empty;
                return false;
            }

            try
            {
                byte[] cipherBytes = Convert.FromBase64String(cipherText);

                using (var memoryStream = new MemoryStream(cipherBytes))
                {
                    // create instance of the DES crypto provider
                    var des = new DESCryptoServiceProvider();

                    // get the IV
                    byte[] iv = new byte[8];
                    memoryStream.Read(iv, 0, iv.Length);

                    // use derive bytes to generate key from password and IV
                    var rfc2898DeriveBytes = new Rfc2898DeriveBytes(password, iv, Iterations);

                    byte[] key = rfc2898DeriveBytes.GetBytes(8);

                    using (var cryptoStream = new CryptoStream(memoryStream, des.CreateDecryptor(key, iv), CryptoStreamMode.Read))
                    using (var streamReader = new StreamReader(cryptoStream))
                    {
                        plainText = streamReader.ReadToEnd();
                        return true;
                    }
                }
            }
            catch (Exception ex)
            {
                Debug.LogError("Dialogue System Menus: Can't decrypt data: + " + ex.Message);
                plainText = string.Empty;
                return false;
            }
        }

#else

        // No encryption on other platforms:

        public static string Encrypt(string plainText, string password)
        {
            return plainText;
        }

        public static bool TryDecrypt(string cipherText, string password, out string plainText)
        {
            plainText = cipherText;
            return true;
        }

#endif

    }

}