using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
using System.Threading.Tasks;

namespace API.Model
{
    public class EncryptDecryptUtility
    {
        protected static string saltValue = "K0r3@GM3";
        protected static string hashAlgorithm = "SHA1";
        protected static int passwordIterations = 5;
        protected static string initVector = "P@s$w0rDGm3KoR3@";
        protected static int keySize = 256;

        /// <summary>
        /// Encrypts specified plaintext using Rijndael symmetric key algorithm
        /// and returns a base64-encoded result.
        /// </summary>
        /// <param name="plainText">Plain Text to Encrypt</param>
        /// <param name="passPhrase">Pass Phrase to use in Password Generation</param>
        /// <returns>Encrypted text encoded into Base 64 text format </returns>
        public static string Encrypt(string plainText, string passPhrase)
        {
            // Convert strings into byte arrays.
            // Let us assume that strings only contain ASCII codes.
            // If strings include Unicode characters, use Unicode, UTF7, or UTF8 
            // encoding.
            byte[] initVectorBytes = Encoding.ASCII.GetBytes(initVector);
            byte[] saltValueBytes = Encoding.ASCII.GetBytes(saltValue);

            // Convert our plaintext into a byte array.
            // Let us assume that plaintext contains UTF8-encoded characters.
            byte[] plainTextBytes = Encoding.UTF8.GetBytes(plainText);

            // First, we must create a password, from which the key will be derived.
            // This password will be generated from the specified passphrase and 
            // salt value. The password will be created using the specified hash 
            // algorithm. Password creation can be done in several iterations.
            var password = new PasswordDeriveBytes(
                passPhrase,
                saltValueBytes,
                hashAlgorithm,
                passwordIterations);

            // Use the password to generate pseudo-random bytes for the encryption
            // key. Specify the size of the key in bytes (instead of bits).
#pragma warning disable 618, 612
            byte[] keyBytes = password.GetBytes(keySize / 8);
#pragma warning restore 618, 612

            // Create uninitialized Rijndael encryption object.
            var symmetricKey = new RijndaelManaged();

            // It is reasonable to set encryption mode to Cipher Block Chaining
            // (CBC). Use default options for other symmetric key parameters.
            symmetricKey.Mode = CipherMode.CBC;

            // Generate encryptor from the existing key bytes and initialization 
            // vector. Key size will be defined based on the number of the key 
            // bytes.
            ICryptoTransform encryptor = symmetricKey.CreateEncryptor(
                keyBytes,
                initVectorBytes);

            var memoryStream = new MemoryStream();

            // Define memory stream which will be used to hold encrypted data.
            var cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write);

            // Start encrypting.
            cryptoStream.Write(plainTextBytes, 0, plainTextBytes.Length);

            // Finish encrypting.
            cryptoStream.FlushFinalBlock();

            // Convert our encrypted data from a memory stream into a byte array.
            byte[] cipherTextBytes = memoryStream.ToArray();

            // Close both streams.
            memoryStream.Close();
            cryptoStream.Close();

            // Convert encrypted data into a base64-encoded string.
            string cipherText = Convert.ToBase64String(cipherTextBytes);

            // Return encrypted string.
            return cipherText;
        }

        /// <summary>
        /// Decrypts specified cipherText using Rijndael symmetric key algorithm
        /// and returns a plain text result.
        /// </summary>
        /// <param name="cipherText">Encryted Text</param>
        /// <param name="passPhrase">Pass Phrase used in Password Generation</param>
        /// <returns></returns>
        public static string Decrypt(string cipherText, string passPhrase)
        {
            // Convert strings defining encryption key characteristics into byte
            // arrays. Let us assume that strings only contain ASCII codes.
            // If strings include Unicode characters, use Unicode, UTF7, or UTF8
            // encoding.
            byte[] initVectorBytes = Encoding.ASCII.GetBytes(initVector);
            byte[] saltValueBytes = Encoding.ASCII.GetBytes(saltValue);

            // Convert our ciphertext into a byte array.
            byte[] cipherTextBytes = Convert.FromBase64String(cipherText);

            // First, we must create a password, from which the key will be 
            // derived. This password will be generated from the specified 
            // passphrase and salt value. The password will be created using
            // the specified hash algorithm. Password creation can be done in
            // several iterations.
            var password = new PasswordDeriveBytes(
                passPhrase,
                saltValueBytes,
                hashAlgorithm,
                passwordIterations);

            // Use the password to generate pseudo-random bytes for the encryption
            // key. Specify the size of the key in bytes (instead of bits).
#pragma warning disable 618, 612
            byte[] keyBytes = password.GetBytes(keySize / 8);
#pragma warning restore 618, 612

            // Create uninitialized Rijndael encryption object.
            var symmetricKey = new RijndaelManaged();

            // It is reasonable to set encryption mode to Cipher Block Chaining
            // (CBC). Use default options for other symmetric key parameters.
            symmetricKey.Mode = CipherMode.CBC;

            // Generate decryptor from the existing key bytes and initialization 
            // vector. Key size will be defined based on the number of the key 
            // bytes.
            ICryptoTransform decryptor = symmetricKey.CreateDecryptor(
                keyBytes,
                initVectorBytes);

            // Define memory stream which will be used to hold encrypted data.
            var memoryStream = new MemoryStream(cipherTextBytes);

            // Define cryptographic stream (always use Read mode for encryption).
            var cryptoStream = new CryptoStream(memoryStream, decryptor, CryptoStreamMode.Read);

            // Since at this point we don't know what the size of decrypted data
            // will be, allocate the buffer long enough to hold ciphertext;
            // plaintext is never longer than ciphertext.
            var plainTextBytes = new byte[cipherTextBytes.Length];

            // Start decrypting.
            int decryptedByteCount = cryptoStream.Read(plainTextBytes, 0, plainTextBytes.Length);

            // Close both streams.
            memoryStream.Close();
            cryptoStream.Close();

            // Convert decrypted data into a string. 
            // Let us assume that the original plaintext string was UTF8-encoded.
            string plainText = Encoding.UTF8.GetString(plainTextBytes, 0, decryptedByteCount);

            // Return decrypted string.   
            return plainText;
        }
    }
}