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

namespace DataModel.Helpers
{
    /// <summary>
    /// Helper methods for encryption / decryption
    /// </summary>
    public class EncryptionHelper
    {
        /// <summary>
        /// Default salt value
        /// </summary>
        private const string DEFAULT_SALT = ")kjdnl3k1jh234a9";

        /// <summary>
        /// Default hashing algorithm to use
        /// </summary>
        private const string DEFAULT_HASH_ALGORITHM = "SHA1";

        /// <summary>
        /// Default number of iterations to do
        /// </summary>
        private const int DEFAULT_PASSWORD_ITERATION = 2;

        /// <summary>
        /// Default initialization vector
        /// </summary>
        private const string DEFAULT_INITIAL_VECTOR = "X8pgVu239uOjdKH1";

        /// <summary>
        /// Default encryption keysize
        /// </summary>
        private const int DEFAULT_KEYSIZE = 256;

        /// <summary>
        /// Encrypts a string
        /// </summary>
        /// <param name="plainText">Text to be encrypted</param>
        /// <param name="password">Password to encrypt with</param>
        /// <param name="salt">Salt to encrypt with</param>
        /// <param name="hashAlgorithm">Can be either SHA1 or MD5</param>
        /// <param name="passwordIterations">Number of iterations to do</param>
        /// <param name="initialVector">Needs to be 16 ASCII characters long</param>
        /// <param name="keySize">Can be 128, 192, or 256</param>
        /// <returns>An encrypted string</returns>
        public static string Encrypt(string plainText, string password, string salt = DEFAULT_SALT, string hashAlgorithm = DEFAULT_HASH_ALGORITHM, int passwordIterations = DEFAULT_PASSWORD_ITERATION, string initialVector = DEFAULT_INITIAL_VECTOR, int keySize = DEFAULT_KEYSIZE)
        {
            if (string.IsNullOrEmpty(plainText))
            {
                return "";
            }

            byte[] initialVectorBytes = Encoding.ASCII.GetBytes(initialVector);
            byte[] saltValueBytes = Encoding.ASCII.GetBytes(salt);
            byte[] plainTextBytes = Encoding.UTF8.GetBytes(plainText);

            PasswordDeriveBytes derivedPassword = new PasswordDeriveBytes(password, saltValueBytes, hashAlgorithm, passwordIterations);
            byte[] keyBytes = derivedPassword.GetBytes(keySize / 8);

            RijndaelManaged symmetricKey = new RijndaelManaged
            {
                Mode = CipherMode.CBC
            };
            byte[] cipherTextBytes = null;

            using (ICryptoTransform encryptor = symmetricKey.CreateEncryptor(keyBytes, initialVectorBytes))
            {
                using (MemoryStream memStream = new MemoryStream())
                {
                    using (CryptoStream cryptoStream = new CryptoStream(memStream, encryptor, CryptoStreamMode.Write))
                    {
                        cryptoStream.Write(plainTextBytes, 0, plainTextBytes.Length);
                        cryptoStream.FlushFinalBlock();
                        cipherTextBytes = memStream.ToArray();
                        memStream.Close();
                        cryptoStream.Close();
                    }
                }
            }

            symmetricKey.Clear();

            return Convert.ToBase64String(cipherTextBytes);
        }

        /// <summary>
        /// Decrypts a string
        /// </summary>
        /// <param name="encrypted">Text to be decrypted</param>
        /// <param name="password">Password to decrypt with</param>
        /// <param name="salt">Salt to decrypt with</param>
        /// <param name="hashAlgorithm">Can be either SHA1 or MD5</param>
        /// <param name="passwordIterations">Number of iterations to do</param>
        /// <param name="initialVector">Needs to be 16 ASCII characters long</param>
        /// <param name="keySize">Can be 128, 192, or 256</param>
        /// <returns>A decrypted string</returns>
        public static string Decrypt(string encrypted, string password, string salt = DEFAULT_SALT, string hashAlgorithm = DEFAULT_HASH_ALGORITHM, int passwordIterations = DEFAULT_PASSWORD_ITERATION, string initialVector = DEFAULT_INITIAL_VECTOR, int keySize = DEFAULT_KEYSIZE)
        {
            if (string.IsNullOrEmpty(encrypted))
            {
                return "";
            }

            byte[] initialVectorBytes = Encoding.ASCII.GetBytes(initialVector);
            byte[] saltValueBytes = Encoding.ASCII.GetBytes(salt);
            byte[] cipherTextBytes = Convert.FromBase64String(encrypted);

            PasswordDeriveBytes derivedPassword = new PasswordDeriveBytes(password, saltValueBytes, hashAlgorithm, passwordIterations);
            byte[] keyBytes = derivedPassword.GetBytes(keySize / 8);

            RijndaelManaged symmetricKey = new RijndaelManaged
            {
                Mode = CipherMode.CBC
            };

            byte[] plainTextBytes = new byte[cipherTextBytes.Length];
            int byteCount = 0;

            using (ICryptoTransform decrypt = symmetricKey.CreateDecryptor(keyBytes, initialVectorBytes))
            {
                using (MemoryStream memStream = new MemoryStream(cipherTextBytes))
                {
                    using (CryptoStream cryptoStream = new CryptoStream(memStream, decrypt, CryptoStreamMode.Read))
                    {

                        byteCount = cryptoStream.Read(plainTextBytes, 0, plainTextBytes.Length);
                        memStream.Close();
                        cryptoStream.Close();
                    }
                }
            }

            symmetricKey.Clear();

            return Encoding.UTF8.GetString(plainTextBytes, 0, byteCount);
        }
    }
}