/*
 * Copyright (c) 2006, Clutch, Inc.
 * Original Author: Jeff Cesnik
 * All rights reserved.
 *
 * - Redistribution and use in source and binary forms, with or without 
 *   modification, are permitted provided that the following conditions are met:
 *
 * - Redistributions of source code must retain the above copyright notice, this
 *   list of conditions and the following disclaimer.
 * - Neither the name of the openmetaverse.org nor the names 
 *   of its contributors may be used to endorse or promote products derived from
 *   this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" 
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE 
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 
 * POSSIBILITY OF SUCH DAMAGE.
 */

using System;
using System.Net;
using System.Net.Sockets;
using System.Threading;

namespace OpenMetaverse
{
    /// <summary>
    /// 
    /// </summary>
    public abstract class UDPBase
    {
        // these abstract methods must be implemented in a derived class to actually do
        // something with the packets that are sent and received.
        protected abstract void PacketReceived(UDPPacketBuffer buffer);
        protected abstract void PacketSent(UDPPacketBuffer buffer, int bytesSent);

        // the port to listen on
        protected int udpPort;

        // the remote endpoint to communicate with
        protected IPEndPoint remoteEndPoint = null;

        // the UDP socket
        private Socket udpSocket;

        // the all important shutdownFlag.
        private volatile bool shutdownFlag = true;

        /// <summary>
        /// Initialize the UDP packet handler in server mode
        /// </summary>
        /// <param name="port">Port to listening for incoming UDP packets on</param>
        public UDPBase(int port)
        {
            udpPort = port;
        }

        /// <summary>
        /// Initialize the UDP packet handler in client mode
        /// </summary>
        /// <param name="endPoint">Remote UDP server to connect to</param>
        public UDPBase(IPEndPoint endPoint)
        {
            remoteEndPoint = endPoint;
            udpPort = 0;
        }

        /// <summary>
        /// 
        /// </summary>
        public void Start()
        {
            if (shutdownFlag)
            {
                const int SIO_UDP_CONNRESET = -1744830452;

                IPEndPoint ipep = new IPEndPoint(Settings.BIND_ADDR, udpPort);
                udpSocket = new Socket(
                    AddressFamily.InterNetwork,
                    SocketType.Dgram,
                    ProtocolType.Udp);
                try
                {
                    // this udp socket flag is not supported under mono, 
                    // so we'll catch the exception and continue
                    udpSocket.IOControl(SIO_UDP_CONNRESET, new byte[] { 0 }, null);
                }
                catch (SocketException)
                {
                    Logger.DebugLog("UDP SIO_UDP_CONNRESET flag not supported on this platform");
                }

                // On at least Mono 3.2.8, multiple UDP sockets can bind to the same port by default.  This means that
                // when running multiple connections, two can occasionally bind to the same port, leading to unexpected
                // errors as they intercept each others messages.  We need to prevent this.  This is not allowed by 
                // default on Windows.
                udpSocket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, false);

                udpSocket.Bind(ipep);

                // we're not shutting down, we're starting up
                shutdownFlag = false;

                // kick off an async receive.  The Start() method will return, the
                // actual receives will occur asynchronously and will be caught in
                // AsyncEndRecieve().
                AsyncBeginReceive();
            }
        }

        /// <summary>
        /// 
        /// </summary>
        public void Stop()
        {
            if (!shutdownFlag)
            {
                // wait indefinitely for a writer lock.  Once this is called, the .NET runtime
                // will deny any more reader locks, in effect blocking all other send/receive
                // threads.  Once we have the lock, we set shutdownFlag to inform the other
                // threads that the socket is closed.
                shutdownFlag = true;
                udpSocket.Close();
            }
        }

        /// <summary>
        /// 
        /// </summary>
        public bool IsRunning
        {
            get { return !shutdownFlag; }
        }

        private void AsyncBeginReceive()
        {
            // allocate a packet buffer
            //WrappedObject<UDPPacketBuffer> wrappedBuffer = Pool.CheckOut();
            UDPPacketBuffer buf = new UDPPacketBuffer();

            if (!shutdownFlag)
            {
                try
                {
                    // kick off an async read
                    udpSocket.BeginReceiveFrom(
                        //wrappedBuffer.Instance.Data,
                        buf.Data,
                        0,
                        UDPPacketBuffer.BUFFER_SIZE,
                        SocketFlags.None,
                        ref buf.RemoteEndPoint,
                        AsyncEndReceive,
                        //wrappedBuffer);
                        buf);
                }
                catch (SocketException e)
                {
                    if (e.SocketErrorCode == SocketError.ConnectionReset)
                    {
                        Logger.Log("SIO_UDP_CONNRESET was ignored, attempting to salvage the UDP listener on port " + udpPort, Helpers.LogLevel.Error);
                        bool salvaged = false;
                        while (!salvaged)
                        {
                            try
                            {
                                udpSocket.BeginReceiveFrom(
                                    //wrappedBuffer.Instance.Data,
                                    buf.Data,
                                    0,
                                    UDPPacketBuffer.BUFFER_SIZE,
                                    SocketFlags.None,
                                    ref buf.RemoteEndPoint,
                                    AsyncEndReceive,
                                    //wrappedBuffer);
                                    buf);
                                salvaged = true;
                            }
                            catch (SocketException) { }
                            catch (ObjectDisposedException) { return; }
                        }

                        Logger.Log("Salvaged the UDP listener on port " + udpPort, Helpers.LogLevel.Info);
                    }
                }
                catch (ObjectDisposedException) { }
            }
        }

        private void AsyncEndReceive(IAsyncResult iar)
        {
            // Asynchronous receive operations will complete here through the call
            // to AsyncBeginReceive
            if (!shutdownFlag)
            {
                // start another receive - this keeps the server going!
                AsyncBeginReceive();

                // get the buffer that was created in AsyncBeginReceive
                // this is the received data
                //WrappedObject<UDPPacketBuffer> wrappedBuffer = (WrappedObject<UDPPacketBuffer>)iar.AsyncState;
                //UDPPacketBuffer buffer = wrappedBuffer.Instance;
                UDPPacketBuffer buffer = (UDPPacketBuffer)iar.AsyncState;

                try
                {
                    // get the length of data actually read from the socket, store it with the
                    // buffer
                    buffer.DataLength = udpSocket.EndReceiveFrom(iar, ref buffer.RemoteEndPoint);

                    // call the abstract method PacketReceived(), passing the buffer that
                    // has just been filled from the socket read.
                    PacketReceived(buffer);
                }
                catch (SocketException) { }
                catch (ObjectDisposedException) { }
                //finally { wrappedBuffer.Dispose(); }
            }
        }

        public void AsyncBeginSend(UDPPacketBuffer buf)
        {
            if (!shutdownFlag)
            {
                try
                {
                    // Profiling heavily loaded clients was showing better performance with 
                    // synchronous UDP packet sending
                    udpSocket.SendTo(
                        buf.Data,
                        0,
                        buf.DataLength,
                        SocketFlags.None,
                        buf.RemoteEndPoint);

                    //udpSocket.BeginSendTo(
                    //    buf.Data,
                    //    0,
                    //    buf.DataLength,
                    //    SocketFlags.None,
                    //    buf.RemoteEndPoint,
                    //    AsyncEndSend,
                    //    buf);
                }
                catch (SocketException) { }
                catch (ObjectDisposedException) { }
            }
        }

        //void AsyncEndSend(IAsyncResult result)
        //{
        //    try
        //    {
        //        UDPPacketBuffer buf = (UDPPacketBuffer)result.AsyncState;
        //        if (!udpSocket.Connected) return;
        //        int bytesSent = udpSocket.EndSendTo(result);

        //        PacketSent(buf, bytesSent);
        //    }
        //    catch (SocketException) { }
        //    catch (ObjectDisposedException) { }
        //}
    }
}