using System;
using System.Collections.Specialized;
using System.Security.Cryptography;
using System.Text;
using System.Web;

namespace infoExpediters
{
    public class SecureQueryString : NameValueCollection

    {

        public SecureQueryString() : base() { }
        //public DateTime dtt;
        public SecureQueryString(string encryptedString)
        {
            deserialize(decrypt(encryptedString));

            // Compare the Expiration Time with the current Time to ensure
            // that the queryString has not expired.

            //dtt=ExpireTime;
            //Commented by Rahul
            //			if (DateTime.Compare(ExpireTime, DateTime.Now) < 0) 
            //			{
            //				throw new ExpiredQueryStringException();
            //			}

            //Commented by Rahul end
        }

        /// <summary>
        /// Returns the encrypted query string.
        /// </summary>
        public string EncryptedString
        {
            get
            {
                return HttpUtility.UrlEncode(encrypt(serialize()));
            }
        }
        //Commented by Rahul
        //		private DateTime _expireTime =DateTime.MaxValue;//Convert.ToDateTime("8 PM");
        //		/// <summary>
        //		/// The timestamp in which the EncryptedString should expire
        //		/// </summary>
        //		public DateTime ExpireTime 
        //		{
        //			get 
        //			{
        //				return _expireTime;
        //			}
        //			set
        //			{
        //				_expireTime = value;
        //			}
        //		}
        //Commented by Rahul end
        /// <summary>
        /// Returns the EncryptedString property.
        /// </summary>
        public override string ToString()
        {
            return EncryptedString;
        }

        /// <summary>
        /// Encrypts a serialized query string 
        /// </summary>
        public string encrypt(string serializedQueryString)
        {
            byte[] buffer = Encoding.ASCII.GetBytes(serializedQueryString);
            TripleDESCryptoServiceProvider des = new TripleDESCryptoServiceProvider();
            MD5CryptoServiceProvider MD5 = new MD5CryptoServiceProvider();
            des.Key = MD5.ComputeHash(ASCIIEncoding.ASCII.GetBytes(cryptoKey));
            des.IV = IV;
            return Convert.ToBase64String(
                des.CreateEncryptor().TransformFinalBlock(
                    buffer,
                    0,
                    buffer.Length
                )
            );
        }

        /// <summary>
        /// Decrypts a serialized query string
        /// </summary>
        public string decrypt(string encryptedQueryString)
        {
            try
            {
                byte[] buffer = Convert.FromBase64String(encryptedQueryString);
                TripleDESCryptoServiceProvider des = new TripleDESCryptoServiceProvider();
                MD5CryptoServiceProvider MD5 = new MD5CryptoServiceProvider();
                des.Key = MD5.ComputeHash(ASCIIEncoding.ASCII.GetBytes(cryptoKey));
                des.IV = IV;
                return Encoding.ASCII.GetString(
                    des.CreateDecryptor().TransformFinalBlock(
                        buffer,
                        0,
                        buffer.Length
                    )
                );
            }
            catch (CryptographicException)
            {
                throw new InvalidQueryStringException();
            }
            catch (FormatException)
            {
                throw new InvalidQueryStringException();
            }
        }

        /// <summary>
        /// Deserializes a decrypted query string and stores it
        /// as name/value pairs.
        /// </summary>
        private void deserialize(string decryptedQueryString)
        {
            string[] nameValuePairs = decryptedQueryString.Split('&');
            for (int i = 0; i < nameValuePairs.Length; i++)
            {
                string[] nameValue = nameValuePairs[i].Split('=');
                if (nameValue.Length == 2)
                {
                    base.Add(nameValue[0], nameValue[1]);
                }
            }
            // Ensure that timeStampKey exists and update the expiration time.
            //Commented by Rahul
            //			if (base[timeStampKey] != null) 
            //				_expireTime = DateTime.Parse(base[timeStampKey]);
            //Commented by Rahul end
        }


        /// <summary>
        /// Serializes the underlying NameValueCollection as a QueryString
        /// </summary>
        public string serialize()
        {
            StringBuilder sb = new StringBuilder();
            foreach (string key in base.AllKeys)
            {
                sb.Append(key);
                sb.Append('=');
                sb.Append(base[key]);
                sb.Append('&');
            }

            // Append timestamp


            //Commented by Rahul
            //			sb.Append(timeStampKey);
            //			sb.Append('=');
            //			sb.Append("12/31/9999 11:59:59 PM");//.ToString().Substring(0,_expireTime.Length-2)("08/09/2004 11:10:10 PM")_expireTime;
            //Commented by Rahul end


            return sb.ToString();
        }
        //Commented by Rahul
        //private const string timeStampKey = "__TimeStamp__";
        //Commented by Rahul end		
        // The key used for generating the encrypted string
        private const string cryptoKey = "ChangeThis!";

        // The Initialization Vector for the DES encryption routine
        private readonly byte[] IV = new byte[8] { 240, 3, 45, 29, 0, 76, 173, 59 };


    }
}