using System;
using System.Runtime.InteropServices;
using System.Security;
using System.Text;


namespace Common.Utils
{
    /// <summary>
    /// An extension class to handle SecureString conversion  
    /// </summary>
    internal static class SecureStringExtensions
    {
        public static readonly Encoding ENCODING = Encoding.UTF8;

        #region methods

        /// <summary>
        /// Convert the content of the SecureString as an array of bytes
        /// </summary>
        /// <param name="password"></param>
        /// <returns> A Byte Array representation of a secure string </returns>
        public static byte[] ConvertToByteArray(this SecureString password)
        {
            if (password == null)
            {
                throw new SecureStringConversionException("Cannot convert a null password");
            }

            IntPtr stringTempPass = IntPtr.Zero;
            string convertedPass;
            try
            {
                stringTempPass = Marshal.SecureStringToGlobalAllocUnicode(password);
                convertedPass = Marshal.PtrToStringUni(stringTempPass);

                if (convertedPass != null)
                    return ENCODING.GetBytes(convertedPass);
                else
                    return null;
            }
            finally
            {
                Marshal.ZeroFreeGlobalAllocUnicode(stringTempPass);
            }
        }

        /// <summary>
        /// Convert the content of a byte array to a secure string 
        /// </summary>
        /// <param name="arrayToConvert"></param>
        /// <returns> The representation of the byte array in a secure string </returns>
        public static SecureString ConvertByteArrayToSecureString(this byte[] arrayToConvert)
        {
            IntPtr stringPointer = IntPtr.Zero;

            if (arrayToConvert.Length == 0)
                throw new ArgumentException("Password is empty");
            stringPointer = Marshal.StringToBSTR(ENCODING.GetString(arrayToConvert));

            try
            {
                return ConvertToSecureString(Marshal.PtrToStringBSTR(stringPointer));
            }

            finally
            {
                Marshal.ZeroFreeBSTR(stringPointer);
                GC.Collect();
            }
        }

        /// <summary>
        /// Convert a secure string to a char array
        /// </summary>
        /// <param name="password"></param>
        /// <returns> A representation of the secure string in a char array </returns>
        public static char[] ConvertToCharArray(this SecureString password)
        {
            char[] charArray = new char[password.Length];
            IntPtr charPass = IntPtr.Zero;

            try
            {
                charPass = Marshal.SecureStringToCoTaskMemUnicode(password);
                Marshal.Copy(charPass, charArray, 0, password.Length);
                return charArray;
            }
            finally
            {
                if (charPass != IntPtr.Zero)
                {
                    Marshal.ZeroFreeGlobalAllocUnicode(charPass);
                }
            }
        }

        /// <summary>
        /// Convert a SecureString to string. Used for compliancy with MSFT WINRM DLL
        /// </summary>
        /// <param name="password"></param>
        /// <returns>a string represetation of a secure string </returns>
        public static string ConvertToString(this SecureString password)
        {
            IntPtr stringPointer = IntPtr.Zero;

            if (password == null)
                throw new ArgumentNullException("Password is empty");
            stringPointer = Marshal.SecureStringToBSTR(password);

            try
            {
                return Marshal.PtrToStringBSTR(stringPointer);
            }
            finally
            {
                Marshal.ZeroFreeBSTR(stringPointer);
            }
        }

        /// <summary>
        /// Convert a String object to SecureString
        /// </summary>
        /// <param name="password"></param>
        /// <returns>A secure string representation of a string object</returns>
        public static SecureString ConvertToSecureString(this string password)
        {
            var securePass = new SecureString();

            foreach (var c in password)
                securePass.AppendChar(c);

            securePass.MakeReadOnly();
            return securePass;
        }

        /// <summary>
        /// Compare the value of secure string object
        /// </summary>
        /// <param name="password"></param>
        /// <param name="value"></param>
        /// <returns>true/false according to the values equality</returns>
        public static bool ValueEquals(this SecureString password, SecureString value)
        {
            IntPtr passBstr = IntPtr.Zero;
            IntPtr valueBstr = IntPtr.Zero;
            try
            {
                passBstr = Marshal.SecureStringToBSTR(password);
                valueBstr = Marshal.SecureStringToBSTR(value);
                int passLength = Marshal.ReadInt32(passBstr, -4);
                int valueLength = Marshal.ReadInt32(valueBstr, -4);

                if (passLength != valueLength)
                    return false;
                for (int x = 0; x < passLength; ++x)
                {
                    byte passByte = Marshal.ReadByte(passBstr, x);
                    byte valueByte = Marshal.ReadByte(valueBstr, x);
                    if (passByte != valueByte)
                        return false;
                }

                return true;
            }
            finally
            {
                if (passBstr != IntPtr.Zero)
                    Marshal.ZeroFreeBSTR(passBstr);
                if (valueBstr != IntPtr.Zero)
                    Marshal.ZeroFreeBSTR(valueBstr);
            }
        }
    }

    public class SecureStringConversionException : Exception
    {
        public SecureStringConversionException()
        {
        }

        public SecureStringConversionException(string message) : base(message)
        {
        }

        public SecureStringConversionException(string message, Exception innerException) : base(message, innerException)
        {
        }
    }
}

#endregion