/*
 *  Authors:  Benton Stark
 * 
 *  Copyright (c) 2007-2009 Starksoft, LLC (http://www.starksoft.com) 
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 * 
 */

using System;
using System.Text;
using System.Net.Sockets;
using System.Threading;
using System.Globalization;
using System.ComponentModel;

namespace Starksoft.Net.Proxy
{
    /// <summary>
    /// HTTP connection proxy class.  This class implements the HTTP standard proxy protocol.
    /// <para>
    /// You can use this class to set up a connection to an HTTP proxy server.  Calling the 
    /// CreateConnection() method initiates the proxy connection and returns a standard
    /// System.Net.Socks.TcpClient object that can be used as normal.  The proxy plumbing
    /// is all handled for you.
    /// </para>
    /// <code>
    /// 
    /// </code>
    /// </summary>
    public class HttpProxyClient : IProxyClient
    {
        private string _proxyHost;
        private int _proxyPort;
        private HttpResponseCodes _respCode;
        private string _respText;
        private TcpClient _tcpClient;

        private const int HTTP_PROXY_DEFAULT_PORT = 8080;
        private const string HTTP_PROXY_CONNECT_CMD = "CONNECT {0}:{1} HTTP/1.0\r\nHost: {0}:{1}\r\n\r\n";
        private const int WAIT_FOR_DATA_INTERVAL = 50; // 50 ms
        private const int WAIT_FOR_DATA_TIMEOUT = 15000; // 15 seconds
        private const string PROXY_NAME = "HTTP";

        private enum HttpResponseCodes
        {
            None = 0,
            Continue = 100,
            SwitchingProtocols = 101,
            OK = 200,
            Created = 201,
            Accepted = 202,
            NonAuthoritiveInformation = 203,
            NoContent = 204,
            ResetContent = 205,
            PartialContent = 206,
            MultipleChoices = 300,
            MovedPermanetly = 301,
            Found = 302,
            SeeOther = 303,
            NotModified = 304,
            UserProxy = 305,
            TemporaryRedirect = 307,
            BadRequest = 400,
            Unauthorized = 401,
            PaymentRequired = 402,
            Forbidden = 403,
            NotFound = 404,
            MethodNotAllowed = 405,
            NotAcceptable = 406,
            ProxyAuthenticantionRequired = 407,
            RequestTimeout = 408,
            Conflict = 409,
            Gone = 410,
            PreconditionFailed = 411,
            RequestEntityTooLarge = 413,
            RequestURITooLong = 414,
            UnsupportedMediaType = 415,
            RequestedRangeNotSatisfied = 416,
            ExpectationFailed = 417,
            InternalServerError = 500,
            NotImplemented = 501,
            BadGateway = 502,
            ServiceUnavailable = 503,
            GatewayTimeout = 504,
            HTTPVersionNotSupported = 505
        }

        /// <summary>
        /// Constructor.
        /// </summary>
        public HttpProxyClient() { }

        /// <summary>
        /// Creates a HTTP proxy client object using the supplied TcpClient object connection.
        /// </summary>
        /// <param name="tcpClient">A TcpClient connection object.</param>
        public HttpProxyClient(TcpClient tcpClient)
        {
            if (tcpClient == null)
                throw new ArgumentNullException("tcpClient");

            _tcpClient = tcpClient;
        }


        /// <summary>
        /// Constructor.  The default HTTP proxy port 8080 is used.
        /// </summary>
        /// <param name="proxyHost">Host name or IP address of the proxy.</param>
        public HttpProxyClient(string proxyHost)
        {
            if (String.IsNullOrEmpty(proxyHost))
                throw new ArgumentNullException("proxyHost");

            _proxyHost = proxyHost;
            _proxyPort = HTTP_PROXY_DEFAULT_PORT;
        }

        /// <summary>
        /// Constructor.  
        /// </summary>
        /// <param name="proxyHost">Host name or IP address of the proxy server.</param>
        /// <param name="proxyPort">Port number for the proxy server.</param>
        public HttpProxyClient(string proxyHost, int proxyPort)
        {
            if (String.IsNullOrEmpty(proxyHost))
                throw new ArgumentNullException("proxyHost");

            if (proxyPort <= 0 || proxyPort > 65535)
                throw new ArgumentOutOfRangeException("proxyPort", "port must be greater than zero and less than 65535");

            _proxyHost = proxyHost;
            _proxyPort = proxyPort;
        }

        /// <summary>
        /// Gets or sets host name or IP address of the proxy server.
        /// </summary>
        public string ProxyHost
        {
            get { return _proxyHost; }
            set { _proxyHost = value; }
        }

        /// <summary>
        /// Gets or sets port number for the proxy server.
        /// </summary>
        public int ProxyPort
        {
            get { return _proxyPort; }
            set { _proxyPort = value; }
        }

        /// <summary>
        /// Gets String representing the name of the proxy. 
        /// </summary>
        /// <remarks>This property will always return the value 'HTTP'</remarks>
        public string ProxyName
        {
            get { return PROXY_NAME; }
        }

        /// <summary>
        /// Gets or sets the TcpClient object. 
        /// This property can be set prior to executing CreateConnection to use an existing TcpClient connection.
        /// </summary>
        public TcpClient TcpClient
        {
            get { return _tcpClient; }
            set { _tcpClient = value; }
        }


        /// <summary>
        /// Creates a remote TCP connection through a proxy server to the destination host on the destination port.
        /// </summary>
        /// <param name="destinationHost">Destination host name or IP address.</param>
        /// <param name="destinationPort">Port number to connect to on the destination host.</param>
        /// <returns>
        /// Returns an open TcpClient object that can be used normally to communicate
        /// with the destination server
        /// </returns>
        /// <remarks>
        /// This method creates a connection to the proxy server and instructs the proxy server
        /// to make a pass through connection to the specified destination host on the specified
        /// port.  
        /// </remarks>
        public TcpClient CreateConnection(string destinationHost, int destinationPort)
        {
            try
            {
                // if we have no connection, create one
                if (_tcpClient == null)
                {
                    if (String.IsNullOrEmpty(_proxyHost))
                        throw new ProxyException("ProxyHost property must contain a value.");

                    if (_proxyPort <= 0 || _proxyPort > 65535)
                        throw new ProxyException("ProxyPort value must be greater than zero and less than 65535");

                    //  create new tcp client object to the proxy server
                    _tcpClient = new TcpClient();

                    // attempt to open the connection
                    _tcpClient.Connect(_proxyHost, _proxyPort);
                }

                //  send connection command to proxy host for the specified destination host and port
                SendConnectionCommand(destinationHost, destinationPort);

                // return the open proxied tcp client object to the caller for normal use
                return _tcpClient;
            }
            catch (SocketException ex)
            {
                throw new ProxyException(String.Format(CultureInfo.InvariantCulture, "Connection to proxy host {0} on port {1} failed.", Utils.GetHost(_tcpClient), Utils.GetPort(_tcpClient)), ex);
            }
        }


        private void SendConnectionCommand(string host, int port)
        {
            NetworkStream stream = _tcpClient.GetStream(); 

            // PROXY SERVER REQUEST
            // =======================================================================
            //CONNECT starksoft.com:443 HTTP/1.0 <CR><LF>
            //HOST starksoft.com:443<CR><LF>
            //[... other HTTP header lines ending with <CR><LF> if required]>
            //<CR><LF>    // Last Empty Line

            string connectCmd = String.Format(CultureInfo.InvariantCulture, HTTP_PROXY_CONNECT_CMD, host, port.ToString(CultureInfo.InvariantCulture));
            byte[] request = ASCIIEncoding.ASCII.GetBytes(connectCmd);

            // send the connect request
            stream.Write(request, 0, request.Length);

            // wait for the proxy server to respond
            WaitForData(stream);

            // PROXY SERVER RESPONSE
            // =======================================================================
            //HTTP/1.0 200 Connection Established<CR><LF>
            //[.... other HTTP header lines ending with <CR><LF>..
            //ignore all of them]
            //<CR><LF>    // Last Empty Line

            // create an byte response array  
            byte[] response = new byte[_tcpClient.ReceiveBufferSize];
            StringBuilder sbuilder = new StringBuilder();
            int bytes = 0;
            long total = 0;

            do
            {
                bytes = stream.Read(response, 0, _tcpClient.ReceiveBufferSize);
                total += bytes;
                sbuilder.Append(System.Text.ASCIIEncoding.UTF8.GetString(response, 0, bytes));
            } while (stream.DataAvailable);

            ParseResponse(sbuilder.ToString());
            
            //  evaluate the reply code for an error condition
            if (_respCode != HttpResponseCodes.OK)
                HandleProxyCommandError(host, port);
        }
        
        private void HandleProxyCommandError(string host, int port)
        {
            string msg;

            switch (_respCode)
            {
                case HttpResponseCodes.None:
                    msg = String.Format(CultureInfo.InvariantCulture, "Proxy destination {0} on port {1} failed to return a recognized HTTP response code.  Server response: {2}", Utils.GetHost(_tcpClient), Utils.GetPort(_tcpClient), _respText);
                    break;                   

                case HttpResponseCodes.BadGateway:
                    //HTTP/1.1 502 Proxy Error (The specified Secure Sockets Layer (SSL) port is not allowed. ISA Server is not configured to allow SSL requests from this port. Most Web browsers use port 443 for SSL requests.)
                    msg = String.Format(CultureInfo.InvariantCulture, "Proxy destination {0} on port {1} responded with a 502 code - Bad Gateway.  If you are connecting to a Microsoft ISA destination please refer to knowledge based article Q283284 for more information.  Server response: {2}", Utils.GetHost(_tcpClient), Utils.GetPort(_tcpClient), _respText);
                    break;

                default:
                    msg = String.Format(CultureInfo.InvariantCulture, "Proxy destination {0} on port {1} responded with a {2} code - {3}", Utils.GetHost(_tcpClient), Utils.GetPort(_tcpClient), ((int)_respCode).ToString(CultureInfo.InvariantCulture), _respText);
                    break;
            }

            //  throw a new application exception 
            throw new ProxyException(msg);
        }

        private void WaitForData(NetworkStream stream)
        {
            int sleepTime = 0;
            while (!stream.DataAvailable)
            {
                Thread.Sleep(WAIT_FOR_DATA_INTERVAL);
                sleepTime += WAIT_FOR_DATA_INTERVAL;
                if (sleepTime > WAIT_FOR_DATA_TIMEOUT)
                    throw new ProxyException(String.Format("A timeout while waiting for the proxy server at {0} on port {1} to respond.", Utils.GetHost(_tcpClient), Utils.GetPort(_tcpClient) ));
            }
        }

        private void ParseResponse(string response)
        {
            string[] data = null;

            //  get rid of the LF character if it exists and then split the string on all CR
            data = response.Replace('\n', ' ').Split('\r');
            
            ParseCodeAndText(data[0]);
        }

        private void ParseCodeAndText(string line)
        {
            int begin = 0;
            int end = 0;
            string val = null;

            if (line.IndexOf("HTTP") == -1)
                throw new ProxyException(String.Format("No HTTP response received from proxy destination.  Server response: {0}.", line));

            begin = line.IndexOf(" ") + 1;
            end = line.IndexOf(" ", begin);

            val = line.Substring(begin, end - begin);
            Int32 code = 0;

            if (!Int32.TryParse(val, out code))
                throw new ProxyException(String.Format("An invalid response code was received from proxy destination.  Server response: {0}.", line));

            _respCode = (HttpResponseCodes)code;
            _respText = line.Substring(end + 1).Trim();
        }



#region "Async Methods"

        private BackgroundWorker _asyncWorker;
        private Exception _asyncException;
        bool _asyncCancelled;

        /// <summary>
        /// Gets a value indicating whether an asynchronous operation is running.
        /// </summary>
        /// <remarks>Returns true if an asynchronous operation is running; otherwise, false.
        /// </remarks>
        public bool IsBusy
        {
            get { return _asyncWorker == null ? false : _asyncWorker.IsBusy; }
        }

        /// <summary>
        /// Gets a value indicating whether an asynchronous operation is cancelled.
        /// </summary>
        /// <remarks>Returns true if an asynchronous operation is cancelled; otherwise, false.
        /// </remarks>
        public bool IsAsyncCancelled
        {
            get { return _asyncCancelled; }
        }

        /// <summary>
        /// Cancels any asychronous operation that is currently active.
        /// </summary>
        public void CancelAsync()
        {
            if (_asyncWorker != null && !_asyncWorker.CancellationPending && _asyncWorker.IsBusy)
            {
                _asyncCancelled = true;
                _asyncWorker.CancelAsync();
            }
        }

        private void CreateAsyncWorker()
        {
            if (_asyncWorker != null)
                _asyncWorker.Dispose();
            _asyncException = null;
            _asyncWorker = null;
            _asyncCancelled = false;
            _asyncWorker = new BackgroundWorker();
        }

        /// <summary>
        /// Event handler for CreateConnectionAsync method completed.
        /// </summary>
        public event EventHandler<CreateConnectionAsyncCompletedEventArgs> CreateConnectionAsyncCompleted;

        /// <summary>
        /// Asynchronously creates a remote TCP connection through a proxy server to the destination host on the destination port.
        /// </summary>
        /// <param name="destinationHost">Destination host name or IP address.</param>
        /// <param name="destinationPort">Port number to connect to on the destination host.</param>
        /// <returns>
        /// Returns an open TcpClient object that can be used normally to communicate
        /// with the destination server
        /// </returns>
        /// <remarks>
        /// This method creates a connection to the proxy server and instructs the proxy server
        /// to make a pass through connection to the specified destination host on the specified
        /// port.  
        /// </remarks>
        public void CreateConnectionAsync(string destinationHost, int destinationPort)
        {
            if (_asyncWorker != null && _asyncWorker.IsBusy)
                throw new InvalidOperationException("The HttpProxy object is already busy executing another asynchronous operation.  You can only execute one asychronous method at a time.");

            CreateAsyncWorker();
            _asyncWorker.WorkerSupportsCancellation = true;
            _asyncWorker.DoWork += new DoWorkEventHandler(CreateConnectionAsync_DoWork);
            _asyncWorker.RunWorkerCompleted += new RunWorkerCompletedEventHandler(CreateConnectionAsync_RunWorkerCompleted);
            Object[] args = new Object[2];
            args[0] = destinationHost;
            args[1] = destinationPort;
            _asyncWorker.RunWorkerAsync(args);
        }

        private void CreateConnectionAsync_DoWork(object sender, DoWorkEventArgs e)
        {
            try
            {
                Object[] args = (Object[])e.Argument;
                e.Result = CreateConnection((string)args[0], (int)args[1]);
            }
            catch (Exception ex)
            {
                _asyncException = ex;
            }
        }

        private void CreateConnectionAsync_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            if (CreateConnectionAsyncCompleted != null)
                CreateConnectionAsyncCompleted(this, new CreateConnectionAsyncCompletedEventArgs(_asyncException, _asyncCancelled, (TcpClient)e.Result));
        }



#endregion

    }
}