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

namespace Assets.Scripts.Common
{
     /// <summary>
     /// AES (Advanced Encryption Standard) implementation with 128-bit key (default)
     /// - 128-bit AES is approved  by NIST, but not the 256-bit AES
     /// - 256-bit AES is slower than the 128-bit AES (by about 40%)
     /// - Use it for secure data protection
     /// - Do NOT use it for data protection in RAM (in most common scenarios)
     /// </summary>
     public static class AES
     {
         public static int KeyLength = 128;
         private const string SaltKey = "ShMG8hLyZ7k~Ge5@";
         private const string VIKey = "~6YUi0Sv5@|{aOZO"; // TODO: Generate random VI each encryption and store it with encrypted value

         public static string Encrypt(byte[] value, string password)
         {
             var keyBytes = new Rfc2898DeriveBytes(password, Encoding.UTF8.GetBytes(SaltKey)).GetBytes(KeyLength / 8);
             var symmetricKey = new RijndaelManaged { Mode = CipherMode.CBC, Padding = PaddingMode.Zeros };
             var encryptor = symmetricKey.CreateEncryptor(keyBytes, Encoding.UTF8.GetBytes(VIKey));

             using (var memoryStream = new MemoryStream())
             {
                 using (var cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write))
                 {
                     cryptoStream.Write(value, 0, value.Length);
                     cryptoStream.FlushFinalBlock();
                     cryptoStream.Close();
                     memoryStream.Close();

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

         public static string Encrypt(string value, string password)
         {
             return Encrypt(Encoding.UTF8.GetBytes(value), password);
         }

         public static string Decrypt(string value, string password)
         {
             var cipherTextBytes = Convert.FromBase64String(value);
             var keyBytes = new Rfc2898DeriveBytes(password, Encoding.UTF8.GetBytes(SaltKey)).GetBytes(KeyLength / 8);
             var symmetricKey = new RijndaelManaged { Mode = CipherMode.CBC, Padding = PaddingMode.None };
             var decryptor = symmetricKey.CreateDecryptor(keyBytes, Encoding.UTF8.GetBytes(VIKey));

             using (var memoryStream = new MemoryStream(cipherTextBytes))
             {
                 using (var cryptoStream = new CryptoStream(memoryStream, decryptor, CryptoStreamMode.Read))
                 {
                     var plainTextBytes = new byte[cipherTextBytes.Length];
                     var decryptedByteCount = cryptoStream.Read(plainTextBytes, 0, plainTextBytes.Length);

                     memoryStream.Close();
                     cryptoStream.Close();

                     return Encoding.UTF8.GetString(plainTextBytes, 0, decryptedByteCount).TrimEnd("\0".ToCharArray());
                 }
             }
         }
     }
}