using Sarand.Net.Standard.Base.App;
using System;
using System.IO;
using System.Security.Cryptography;

namespace Sarand.Net.Standard.Base.Data
{
	//=======================================================================
	public static class SacsAesIvCrypter
	{
		//-------------------------------------------------------------------
		// Properties.
		public static String AesIvDelimiter { get; } = ";";
		public static String AesIvPrefix { get; } = "AESIV:";

		//-------------------------------------------------------------------
		// Ref. https://xamarinhelp.com/cryptography-in-xamarin-forms/
		// For reversible encryption, AES is generally the recommended standard.
		// AES 256 requires a 32 byte key to encrypt.
		// Either generate a 32 byte key or use any string and convert it into a key with CreateKey.
		// NB The salt will remain the same here for each key generated - it does not need to be randomized as with hashing.
		//-------------------------------------------------------------------
		private static byte[] CreateKey(string password, int keyBytes = 32)
		{
			byte[] salt = new byte[] { 80, 70, 60, 50, 40, 30, 20, 10 };
			int iterations = 300;
			DeriveBytes keyGenerator = new Rfc2898DeriveBytes(password, salt, iterations, HashAlgorithmName.SHA256);
			return keyGenerator.GetBytes(keyBytes);
		}

		//-------------------------------------------------------------------
		// Encrypt String.
		// Return the encrypted text with the IV appended to the end.
		// In AES, the IV is a randomizer, making sure that no two identical messages ever give the same encrypted output.
		// The IV can be public and does not need to be hidden.
		//-------------------------------------------------------------------
		public static string Encrypt(this string clearValue, string encryptionKey)
		{
			using (Aes aes = Aes.Create())
			{
				aes.Key = CreateKey(encryptionKey);
				byte[] aesIV = aes.IV;
				byte[] encrypted = Encrypt(clearValue, aes.Key, aesIV);
				return Convert.ToBase64String(encrypted) + AesIvDelimiter + Convert.ToBase64String(aesIV);
			}
		}
		//-------------------------------------------------------------------
		public static byte[] Encrypt(string plainText, byte[] key, byte[] iv)
		{
			if (plainText == null || plainText.Length <= 0) throw new ArgumentNullException($"{nameof(plainText)}");
			if (key == null || key.Length <= 0) throw new ArgumentNullException($"{nameof(key)}");
			if (iv == null || iv.Length <= 0) throw new ArgumentNullException($"{nameof(iv)}");
			byte[] encrypted;
			using (Aes aes = Aes.Create())
			{
				aes.Key = key;
				aes.IV = iv;
				using (MemoryStream memoryStream = new MemoryStream())
				{
					using (ICryptoTransform encryptor = aes.CreateEncryptor())
					using (CryptoStream cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write))
					using (StreamWriter streamWriter = new StreamWriter(cryptoStream))
					{
						streamWriter.Write(plainText);
					}
					encrypted = memoryStream.ToArray();
				}
			}
			return encrypted;
		}

		//-------------------------------------------------------------------
		// Decrypt String.
		// Decryption requires the encrypted value and the secret key.
		// This function is directly related to the above encryption process and will
		// assume that the IV is at the end of the string passed in.
		// To decrypt a message encrypted by another function, the IV will have to be passed explicitly.
		//-------------------------------------------------------------------
		public static string Decrypt(this string encryptedValue, string encryptionKey)
		{
			String[] valueParts = encryptedValue.Split(new String[] { AesIvDelimiter }, StringSplitOptions.None);
			if (valueParts.Length != 2)
			{
				SaLogger.Warn("SacsAesIvCrypter.Decrypt Missing IV - assuming not encrypted");
				return encryptedValue;
				//throw new CryptographicException("Decrypt failure: Missing IV");
			}
			return Decrypt(Convert.FromBase64String(valueParts[0]), CreateKey(encryptionKey), Convert.FromBase64String(valueParts[1]));
		}
		//-------------------------------------------------------------------
		public static string Decrypt(byte[] cipherText, byte[] key, byte[] iv)
		{
			if (cipherText == null || cipherText.Length <= 0) throw new ArgumentNullException($"{nameof(cipherText)}");
			if (key == null || key.Length <= 0) throw new ArgumentNullException($"{nameof(key)}");
			if (iv == null || iv.Length <= 0) throw new ArgumentNullException($"{nameof(iv)}");

			string plaintext = "";
			using (Aes aes = Aes.Create())
			{
				aes.Key = key;
				aes.IV = iv;
				using (MemoryStream memoryStream = new MemoryStream(cipherText))
				using (ICryptoTransform decryptor = aes.CreateDecryptor())
				using (CryptoStream cryptoStream = new CryptoStream(memoryStream, decryptor, CryptoStreamMode.Read))
				using (StreamReader streamReader = new StreamReader(cryptoStream))
					plaintext = streamReader.ReadToEnd();
			}
			return plaintext;
		}

		//-------------------------------------------------------------------
	}
	//=======================================================================
}