using System;
using System.Collections.Generic;
using System.Text;
using System.Security.Cryptography;
using System.Security;

namespace DBToolControls {
    public sealed class EncryptionHelper {
        private EncryptionHelper() { }
        private static UnicodeEncoding byteConverter = new UnicodeEncoding();

        public static string EncryptString(string key, string stringToEncrypt) {
            if (key.Length == 0) return stringToEncrypt;
            byte[] dataToEncrypt = byteConverter.GetBytes(stringToEncrypt);
            return ByteArrayToHexString(AESEncrypt(dataToEncrypt, CreateCryptoProvider(key)));
        }

        public static string DecryptString(string key, string encryptedData) {
            if (key.Length == 0) return encryptedData;
            byte[] decryptedData = AESDecrypt(HexStringToByteArray(encryptedData), CreateCryptoProvider(key));
            return byteConverter.GetString(decryptedData);
        }

        public static SecureString DecryptStringAsSecureString(string key, string encryptedData) {
            SecureString secStr = new SecureString();
            if (key.Length == 0) {
                foreach(char c in encryptedData)
                    secStr.AppendChar(c);
            } else {
                byte[] decryptedData = AESDecrypt(HexStringToByteArray(encryptedData), CreateCryptoProvider(key));
                foreach (char c in byteConverter.GetString(decryptedData).ToCharArray())
                    secStr.AppendChar(c);
            }
            return secStr;
        }

        private static AesCryptoServiceProvider CreateCryptoProvider(String key) {
            byte[] salt  = {185, 209, 196, 142,  52, 143, 231, 113,
                            250,  70,  74, 119, 161, 120, 251,   7,
                            220, 254, 173,  80, 209, 217, 253,   8,
                            179, 134, 239, 176, 139,  20,  47, 116,
                             76, 253, 164, 195,   7,  97,  87, 245,
                            129, 183,  30,  70, 232, 203,  86, 117};
            List<byte> keyAsByteList = new List<byte>(byteConverter.GetBytes(key.ToCharArray())).FindAll(b => b != 0);

            
            byte[] sBytes = new byte[48];
            for(int i=0; i<48; i++) {
                sBytes[i] = keyAsByteList[i % keyAsByteList.Count];
            }

            byte[] returnIV = new byte[16];
            for (int i = 0; i < 16; i++) {
                returnIV[i] = (byte)(salt[i] ^ sBytes[i]);
            }

            byte[] returnKey = new byte[32];
            for (int i = 16; i < 48; i++) {
                returnKey[i-16] = (byte)(salt[i] ^ sBytes[i]);
            }

            AesCryptoServiceProvider returnValue = new AesCryptoServiceProvider();
            returnValue.IV = returnIV;
            returnValue.Key = returnKey;
            return returnValue;
        }

        private static byte[] AESEncrypt(byte[] DataToEncrypt, AesCryptoServiceProvider aes) {
            return aes.CreateEncryptor().TransformFinalBlock(DataToEncrypt, 0, DataToEncrypt.Length);
        }

        private static byte[] AESDecrypt(byte[] DataToDecrypt, AesCryptoServiceProvider aes) {
            return aes.CreateDecryptor().TransformFinalBlock(DataToDecrypt, 0, DataToDecrypt.Length);
        }

        private static string ByteArrayToHexString(byte[] data) {
            StringBuilder sb = new StringBuilder();
            foreach (byte b in data)
                sb.Append(String.Format("{0:X2}", b));
            return sb.ToString();
        }

        private static byte[] HexStringToByteArray(string data) {
            if (data.Length % 2 == 1) throw new CryptographicException("Invalid data");
            byte[] bytes = new byte[data.Length / 2];
            for (int i = 0; i < data.Length; i += 2)
                bytes[i/2] = Byte.Parse(data.Substring(i, 2), System.Globalization.NumberStyles.HexNumber);
            return bytes;
        }
    }
}