Server-side Google Analytics Transactions

using System;
using System.Net;

namespace Middelpat.GoogleAnalytics
{
    public class GoogleRequest
    {
        private const string BASE_URL = "http://www.google-analytics.com/__utm.gif?";

        private const string ANALYTICS_VERSION = "5.3.7";
        private const string LANGUAGE_ENCODING = "UTF-8";
        private const string BROWSER_JAVA_ENABLED = "0";

        //Required parameters but not necessary for us, so just post a default
        private const string SCREEN_RESOLUTION = "1680x1050";
        private const string SCREEN_COLOR_DEPTH = "32-bit";
        private const string FLASH_VERSION = "11.5%20r31";
        private const string REFERAL = "0";

        //Internal request counter. Max requests = 500 per session
        private int _RequestCount = 0;

        private Random rand;

        /// <summary>
        /// Initialize a new GoogleRequest
        /// </summary>
        /// <param name="accountCode">Your Google tracking code (e.g. UA-12345678-1)</param>
        public GoogleRequest(string accountCode)
        {
            rand = new Random();

            _RequestCount = 0;
            AccountCode = accountCode;
        }

        /// <summary>
        /// Send the request to the google servers!
        /// </summary>
        /// <param name="eventObject">A corresponding Transaction, Page or Event</param>
        public void SendRequest(IGoogleEvent eventObject)
        {
            string requestUrl = BASE_URL + CreateParameterString() + "&" + eventObject.CreateParameterString();

            FireRequest(requestUrl);

            //A transaction also has subrequests for the TransactionItems
            if (eventObject is Transaction)
            {
                Transaction trans = eventObject as Transaction;

                foreach (TransactionItem transItem in trans.Items)
                {
                    FireRequest(BASE_URL + CreateParameterString() + "&" + transItem.CreateParameterString());
                }
            }
        }

        private void FireRequest(string url)
        {
            if (_RequestCount < 500)
            {
                _RequestCount++;

                WebRequest GaRequest = WebRequest.Create(url);

                GaRequest.BeginGetResponse(r =>
                {
                    try
                    {
                        // we don't need the response so this is the end of the request
                        var reponse = GaRequest.EndGetResponse(r);
                    }
                    catch
                    {
                        //eat the error 
                    }
                }, null);
            }
        }

        private string CreateParameterString()
        {
            return string.Format("utmwv={0}&utms={1}&utmn={2}&utmhn={3}&utmsr{4}&utmvp={5}&utmsc={6}&utmul={7}&utmje={8}&utmfl={9}&utmhid={10}&utmr={11}&utmp={12}&utmac={13}&utmcc={14}",
                                  ANALYTICS_VERSION,
                                  _RequestCount,
                                  GenerateRandomId(),
                                  HostName,
                                  SCREEN_RESOLUTION,
                                  SCREEN_RESOLUTION,
                                  SCREEN_COLOR_DEPTH,
                                  Culture,
                                  BROWSER_JAVA_ENABLED,
                                  FLASH_VERSION,
                                  GenerateRandomId(),
                                  "-",
                                  PageTitle,
                                  AccountCode,
                                  GetUtmcCookieString());
        }

        /// <summary>
        /// (utmn) A random id for each gif to prevent caching
        /// </summary>
        /// <returns></returns>
        private string GenerateRandomId()
        {
            string randomId = "";
      
            for (int i = 0; i < 10; i++)
            {
                randomId += rand.Next(9).ToString();
            }

            return randomId;
        }

        private int DomainHash
        {
            get
            {
                if (HostName != null)
                {
                    int a = 1;
                    int c = 0;
                    int h;
                    char chrCharacter;
                    int intCharacter;

                    a = 0;
                    for (h = HostName.Length - 1; h >= 0; h--)
                    {
                        chrCharacter = char.Parse(HostName.Substring(h, 1));
                        intCharacter = (int)chrCharacter;
                        a = (a << 6 & 268435455) + intCharacter + (intCharacter << 14);
                        c = a & 266338304;
                        a = c != 0 ? a ^ c >> 21 : a;
                    }

                    return a;
                }
                return 0;
            }
        }

        private string _UtmcCookieString = null;
        //The cookie collection string (we fake it)
        private string GetUtmcCookieString()
        {
            if (_UtmcCookieString == null)
            {
                //create the unix timestamp
                TimeSpan span = (DateTime.Now - new DateTime(1970, 1, 1, 0, 0, 0, 0).ToLocalTime());
                int timeStampCurrent = (int)span.TotalSeconds;

                string utma = String.Format("{0}.{1}.{2}.{3}.{4}.{5}",
                                            DomainHash,
                                            int.Parse(rand.Next(1000000000).ToString()),
                                            timeStampCurrent,
                                            timeStampCurrent,
                                            timeStampCurrent,
                                            "2");

                //referral information
                string utmz = String.Format("{0}.{1}.{2}.{3}.utmcsr={4}|utmccn={5}|utmcmd={6}",
                                            DomainHash,
                                            timeStampCurrent,
                                            "1",
                                            "1",
                                            "(direct)",
                                            "(direct)",
                                            "(none)");

                _UtmcCookieString = Uri.EscapeDataString(String.Format("__utma={0};+__utmz={1};", utma, utmz));
            }

            return (_UtmcCookieString);
        }

        #region get set

        private string _AccountCode;
        /// <summary>                           
        /// Your Google tracking code (e.g. UA-12345678-1)
        /// </summary>        
        public string AccountCode
        {
            get
            {
                return _AccountCode;
            }
            set
            {
                _AccountCode = value;
            }
        }

        private string _Culture;
        /// <summary>
        /// The language of the customer (e.g. nl-NL)
        /// </summary>
        public string Culture
        {
            get
            {
                if (string.IsNullOrWhiteSpace(_Culture))
                {
                    _Culture = "nl-NL";
                }

                return _Culture;
            }
            set
            {
                _Culture = value;
            }
        }

        private Uri _HostName;            
        /// <summary>
        /// The hostname of the website making the request (e.g. www.google.com)
        /// </summary>        
        public string HostName
        {
            get
            {
                return _HostName.Host;
            }
            set
            {
                _HostName = new Uri(value);
            }
        }

        private string _PageTitle;
        /// <summary>
        /// The title of the page making the request
        /// </summary>
        public string PageTitle
        {
            get
            {
                if (string.IsNullOrWhiteSpace(_PageTitle))
                {
                    _PageTitle = "ShoppingCart";
                }

                return _PageTitle;
            }
            set
            {
                _PageTitle = value;
            }
        }

        #endregion
    }
}