/*
 * Copyright (c) Contributors, http://opensimulator.org/
 * See CONTRIBUTORS.TXT for a full list of copyright holders.
 *
 * 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.
 *     * Redistributions in binary form must reproduce the above copyright
 *       notice, this list of conditions and the following disclaimer in the
 *       documentation and/or other materials provided with the distribution.
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 *       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 DEVELOPERS ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

using System;
using System.Collections;
using System.Collections.Generic;
using System.Net;
using System.Net.Sockets;
using System.Reflection;
using OpenMetaverse.Packets;
using log4net;
using OpenSim.Framework;
using OpenSim.Framework.Communications.Cache;
using OpenSim.Region.Environment.Scenes;

namespace OpenSim.Region.ClientStack.LindenUDP
{
    /// <summary>
    /// This class handles the initial UDP circuit setup with a client and passes on subsequent packets to the LLPacketServer
    /// </summary>
    public class LLUDPServer : ILLClientStackNetworkHandler, IClientNetworkServer
    {
        private static readonly ILog m_log = LogManager.GetLogger(MethodBase.GetCurrentMethod().DeclaringType);

        /// <value>
        /// The client circuits established with this UDP server.  If a client exists here we can also assume that
        /// it is populated in clientCircuits_reverse and proxyCircuits (if relevant)
        /// </value>
        protected Dictionary<EndPoint, uint> clientCircuits = new Dictionary<EndPoint, uint>();
        public Hashtable clientCircuits_reverse = Hashtable.Synchronized(new Hashtable());
        protected Dictionary<uint, EndPoint> proxyCircuits = new Dictionary<uint, EndPoint>();
        
        private Socket m_socket;
        protected IPEndPoint ServerIncoming;
        protected byte[] RecvBuffer = new byte[4096];
        protected byte[] ZeroBuffer = new byte[8192];

        /// <value>
        /// This is an endpoint that is reused where we don't need to protect the information from potentially
        /// being stomped on by other threads.
        /// </value>
        protected EndPoint reusedEpSender = new IPEndPoint(IPAddress.Any, 0);
        
        protected int proxyPortOffset;
        
        protected AsyncCallback ReceivedData;
        protected LLPacketServer m_packetServer;
        protected Location m_location;

        protected uint listenPort;
        protected bool Allow_Alternate_Port;
        protected IPAddress listenIP = IPAddress.Parse("0.0.0.0");
        protected IScene m_localScene;
        protected AssetCache m_assetCache;

        /// <value>
        /// Manages authentication for agent circuits
        /// </value>
        protected AgentCircuitManager m_circuitManager;

        public IScene LocalScene
        {
            set
            {
                m_localScene = value;
                m_packetServer.LocalScene = m_localScene;
                m_location = new Location(m_localScene.RegionInfo.RegionHandle);
            }
        }

        public ulong RegionHandle
        {
            get { return m_location.RegionHandle; }
        }

        Socket IClientNetworkServer.Server
        {
            get { return m_socket; }
        }

        public bool HandlesRegion(Location x)
        {
            return x == m_location;
        }

        public void AddScene(Scene x)
        {
            LocalScene = x;
        }

        public void Start()
        {
            ServerListener();
        }

        public void Stop()
        {
            m_socket.Close();
        }

        public LLUDPServer()
        {
        }

        public LLUDPServer(
            IPAddress _listenIP, ref uint port, int proxyPortOffset, bool allow_alternate_port, ClientStackUserSettings userSettings, 
            AssetCache assetCache, AgentCircuitManager authenticateClass)
        {
            Initialise(_listenIP, ref port, proxyPortOffset, allow_alternate_port, userSettings, assetCache, authenticateClass);
        }

        /// <summary>
        /// Initialize the server
        /// </summary>
        /// <param name="_listenIP"></param>
        /// <param name="port"></param>
        /// <param name="proxyPortOffsetParm"></param>
        /// <param name="allow_alternate_port"></param>
        /// <param name="userSettings"></param>
        /// <param name="assetCache"></param>
        /// <param name="circuitManager"></param>
        public void Initialise(
            IPAddress _listenIP, ref uint port, int proxyPortOffsetParm, bool allow_alternate_port, ClientStackUserSettings userSettings,
            AssetCache assetCache, AgentCircuitManager circuitManager)
        {
            proxyPortOffset = proxyPortOffsetParm;
            listenPort = (uint) (port + proxyPortOffsetParm);
            listenIP = _listenIP;
            Allow_Alternate_Port = allow_alternate_port;
            m_assetCache = assetCache;
            m_circuitManager = circuitManager;
            CreatePacketServer(userSettings);

            // Return new port
            // This because in Grid mode it is not really important what port the region listens to as long as it is correctly registered.
            // So the option allow_alternate_ports="true" was added to default.xml
            port = (uint)(listenPort - proxyPortOffsetParm);
        }

        protected virtual void CreatePacketServer(ClientStackUserSettings userSettings)
        {
            new LLPacketServer(this, userSettings);
        }

        /// <summary>
        /// This method is called every time that we receive new UDP data. 
        /// </summary>
        /// <param name="result"></param>
        protected virtual void OnReceivedData(IAsyncResult result)
        {
            Packet packet = null;
            int numBytes = 1;
            EndPoint epSender = new IPEndPoint(IPAddress.Any, 0);

            if (EndReceive(out numBytes, result, ref epSender))
            {
                // Make sure we are getting zeroes when running off the
                // end of grab / degrab packets from old clients
                //
                int z;
                for (z = numBytes ; z < RecvBuffer.Length ; z++)
                    RecvBuffer[z] = 0;

                int packetEnd = numBytes - 1;

                try
                {
                    packet = PacketPool.Instance.GetPacket(RecvBuffer, ref packetEnd, ZeroBuffer);
                }
                catch (MalformedDataException e)
                {
                    m_log.DebugFormat("[CLIENT]: Dropped Malformed Packet due to MalformedDataException: {0}", e.StackTrace);
                }
                catch (IndexOutOfRangeException e)
                {
                    m_log.DebugFormat("[CLIENT]: Dropped Malformed Packet due to IndexOutOfRangeException: {0}", e.StackTrace);
                }
                catch (Exception e)
                {
                    m_log.Debug("[CLIENT]: " + e);
                }
            }    
            
            EndPoint epProxy = null;
            
            // If we've received a use circuit packet, then we need to decode an endpoint proxy, if one exists, before 
            // allowing the RecvBuffer to be overwritten by the next packet. 
            if (packet != null && packet.Type == PacketType.UseCircuitCode)
            {
                epProxy = epSender;
                if (proxyPortOffset != 0)
                {
                    epSender = ProxyCodec.DecodeProxyMessage(RecvBuffer, ref numBytes);
                }
            }
            
            BeginReceive(); 

            if (packet != null)
            {
                if (packet.Type == PacketType.UseCircuitCode)
                    AddNewClient((UseCircuitCodePacket)packet, epSender, epProxy);                                  
                else
                    ProcessInPacket(packet, epSender);
            }
        }
        
        /// <summary>
        /// Process a successfully received packet.
        /// </summary>
        /// <param name="packet"></param>
        /// <param name="epSender"></param>
        protected virtual void ProcessInPacket(Packet packet, EndPoint epSender)
        {
            try
            {
                // do we already have a circuit for this endpoint
                uint circuit;
                bool ret;
                
                lock (clientCircuits)
                {
                    ret = clientCircuits.TryGetValue(epSender, out circuit);
                }

                if (ret)
                {
                    //if so then send packet to the packetserver
                    //m_log.DebugFormat("[UDPSERVER]: For endpoint {0} got packet {1}", epSender, packet.Type);

                    m_packetServer.InPacket(circuit, packet);
                }
            }
            catch (Exception e)
            {
                m_log.Error("[CLIENT]: Exception in processing packet - ignoring: ", e);
            }           
        }

        /// <summary>
        /// Begin an asynchronous receive of the next bit of raw data
        /// </summary>
        protected virtual void BeginReceive()
        {
            try
            {
                m_socket.BeginReceiveFrom(
                     RecvBuffer, 0, RecvBuffer.Length, SocketFlags.None, ref reusedEpSender, ReceivedData, null);
            }
            catch (SocketException)
            {
                // We don't need to see this error, reset connection and get next UDP packet off the buffer
                // If the UDP packet is part of the same stream, this will happen several hundreds of times before
                // the next set of UDP data is for a valid client.
                //m_log.ErrorFormat("[CLIENT]: BeginRecieve threw exception " + e.Message + ": " + e.StackTrace );
                
                // ENDLESS LOOP ON PURPOSE!
                ResetEndPoint();
            }
        }
        
        /// <summary>
        /// Finish the process of asynchronously receiving the next bit of raw data
        /// </summary>
        /// <param name="numBytes">The number of bytes received.  Will return 0 if no bytes were recieved
        /// <param name="result"></param>
        /// <param name="epSender">The sender of the data</param>
        /// <returns></returns>
        protected virtual bool EndReceive(out int numBytes, IAsyncResult result, ref EndPoint epSender)
        {
            bool hasReceivedOkay = false;
            numBytes = 0;
            
            try
            {
                numBytes = m_socket.EndReceiveFrom(result, ref epSender);
                hasReceivedOkay = true;
            }
            catch (SocketException e)
            {
                // TODO : Actually only handle those states that we have control over, re-throw everything else,
                // TODO: implement cases as we encounter them.
                //m_log.Error("[[CLIENT]: ]: Connection Error! - " + e.ToString());
                switch (e.SocketErrorCode)
                {
                    case SocketError.AlreadyInProgress:
                        return hasReceivedOkay;

                    case SocketError.NetworkReset:
                    case SocketError.ConnectionReset:
                        break;

                    default:
                        throw;
                }
            }
            catch (ObjectDisposedException e)
            {
                m_log.DebugFormat("[CLIENT]: ObjectDisposedException: Object {0} disposed.", e.ObjectName);
                // Uhh, what object, and why? this needs better handling.
            }      
            
            return hasReceivedOkay;
        }

        private void ResetEndPoint()
        {
            try
            {
                CloseEndPoint(reusedEpSender);
            }
            catch (Exception a)
            {
                m_log.Error("[UDPSERVER]: " + a);
            }

            // ENDLESS LOOP ON PURPOSE!
            
            // We need to purge the UDP stream of crap from the client that disconnected nastily or the UDP server will die
            // The only way to do that is to beginreceive again!
            BeginReceive();

            try
            {                
               // m_socket.BeginReceiveFrom(
                 //   RecvBuffer, 0, RecvBuffer.Length, SocketFlags.None, ref reusedEpSender, ReceivedData, null);

                // Ter: For some stupid reason ConnectionReset basically kills our async event structure..
                // so therefore..  we've got to tell the server to BeginReceiveFrom again.
                // This will happen over and over until we've gone through all packets
                // sent to and from this particular user.
                // Stupid I know..
                // but Flusing the buffer would be even more stupid...  so, we're stuck with this ugly method.
            }
            catch (SocketException e)
            {
                m_log.DebugFormat("[UDPSERVER]: Exception {0} : {1}", e.Message, e.StackTrace );
            }
        }

        private void CloseEndPoint(EndPoint sender)
        {
            uint circuit;
            lock (clientCircuits)
            {
                if (clientCircuits.TryGetValue(sender, out circuit))
                {
                    m_packetServer.CloseCircuit(circuit);
                }
            }
        }

        /// <summary>
        /// Add a new client circuit.
        /// </summary>
        /// <param name="packet"></param>
        /// <param name="epSender"></param>
        /// <param name="epProxy"></param>
        protected virtual void AddNewClient(UseCircuitCodePacket useCircuit, EndPoint epSender, EndPoint epProxy)
        {
            //Slave regions don't accept new clients
            if (m_localScene.Region_Status != RegionStatus.SlaveScene)
            {                
                bool isNewCircuit = false;
                
                lock (clientCircuits)
                {
                    if (!clientCircuits.ContainsKey(epSender))  
                    {
                        m_log.DebugFormat(
                            "[CLIENT]: Adding new circuit for agent {0}, circuit code {1}", 
                            useCircuit.CircuitCode.ID, useCircuit.CircuitCode.Code);
                        
                        clientCircuits.Add(epSender, useCircuit.CircuitCode.Code);
                        
                        isNewCircuit = true;
                    }
                }

                if (isNewCircuit)
                {
                    // This doesn't need locking as it's synchronized data
                    clientCircuits_reverse[useCircuit.CircuitCode.Code] = epSender;

                    lock (proxyCircuits)
                    {
                        proxyCircuits[useCircuit.CircuitCode.Code] = epProxy;
                    }

                    m_packetServer.AddNewClient(epSender, useCircuit, m_assetCache, m_circuitManager, epProxy);
                }
            }            
            
            // Ack the UseCircuitCode packet
            PacketAckPacket ack_it = (PacketAckPacket)PacketPool.Instance.GetPacket(PacketType.PacketAck);
            // TODO: don't create new blocks if recycling an old packet
            ack_it.Packets = new PacketAckPacket.PacketsBlock[1];
            ack_it.Packets[0] = new PacketAckPacket.PacketsBlock();
            ack_it.Packets[0].ID = useCircuit.Header.Sequence;
            ack_it.Header.Reliable = false;
            SendPacketTo(ack_it.ToBytes(), ack_it.ToBytes().Length, SocketFlags.None, useCircuit.CircuitCode.Code);
            
            PacketPool.Instance.ReturnPacket(useCircuit);
        }

        public void ServerListener()
        {
            uint newPort = listenPort;
            m_log.Info("[UDPSERVER]: Opening UDP socket on " + listenIP + " " + newPort + ".");

            ServerIncoming = new IPEndPoint(listenIP, (int)newPort);
            m_socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
            m_socket.Bind(ServerIncoming);
            // Add flags to the UDP socket to prevent "Socket forcibly closed by host"
            // uint IOC_IN = 0x80000000;
            // uint IOC_VENDOR = 0x18000000;
            // uint SIO_UDP_CONNRESET = IOC_IN | IOC_VENDOR | 12;
            // TODO: this apparently works in .NET but not in Mono, need to sort out the right flags here.
            // m_socket.IOControl((int)SIO_UDP_CONNRESET, new byte[] { Convert.ToByte(false) }, null);

            listenPort = newPort;

            m_log.Info("[UDPSERVER]: UDP socket bound, getting ready to listen");

            ReceivedData = OnReceivedData;
            m_socket.BeginReceiveFrom(
                RecvBuffer, 0, RecvBuffer.Length, SocketFlags.None, ref reusedEpSender, ReceivedData, null);

            m_log.Info("[UDPSERVER]: Listening on port " + newPort);
        }

        public virtual void RegisterPacketServer(LLPacketServer server)
        {
            m_packetServer = server;
        }

        public virtual void SendPacketTo(byte[] buffer, int size, SocketFlags flags, uint circuitcode)
            //EndPoint packetSender)
        {
            // find the endpoint for this circuit
            EndPoint sendto;
            try 
            {
                sendto = (EndPoint)clientCircuits_reverse[circuitcode];
            } 
            catch 
            {
                // Exceptions here mean there is no circuit
                m_log.Warn("[CLIENT]: Circuit not found, not sending packet");
                return;
            }

            if (sendto != null)
            {
                //we found the endpoint so send the packet to it
                if (proxyPortOffset != 0)
                {
                    //MainLog.Instance.Verbose("UDPSERVER", "SendPacketTo proxy " + proxyCircuits[circuitcode].ToString() + ": client " + sendto.ToString());
                    ProxyCodec.EncodeProxyMessage(buffer, ref size, sendto);
                    m_socket.SendTo(buffer, size, flags, proxyCircuits[circuitcode]);
                }
                else
                {
                    //MainLog.Instance.Verbose("UDPSERVER", "SendPacketTo : client " + sendto.ToString());
                    try
                    {
                        m_socket.SendTo(buffer, size, flags, sendto);
                    }
                    catch (SocketException SockE)
                    {
                        m_log.ErrorFormat("[UDPSERVER]: Caught Socket Error in the send buffer!. {0}",SockE.ToString());
                    }
                }
            }
        }

        public virtual void RemoveClientCircuit(uint circuitcode)
        {
            EndPoint sendto;
            if (clientCircuits_reverse.Contains(circuitcode))
            {
                sendto = (EndPoint)clientCircuits_reverse[circuitcode];

                clientCircuits_reverse.Remove(circuitcode);

                lock (clientCircuits)
                {
                    if (sendto != null)
                    {
                        clientCircuits.Remove(sendto);
                    }
                    else
                    {
                        m_log.DebugFormat(
                            "[CLIENT]: endpoint for circuit code {0} in RemoveClientCircuit() was unexpectedly null!", circuitcode);
                    }
                }
                lock (proxyCircuits)
                {
                    proxyCircuits.Remove(circuitcode);
                }
            }
        }

        public void RestoreClient(AgentCircuitData circuit, EndPoint userEP, EndPoint proxyEP)
        {
            //MainLog.Instance.Verbose("UDPSERVER", "RestoreClient");

            UseCircuitCodePacket useCircuit = new UseCircuitCodePacket();
            useCircuit.CircuitCode.Code = circuit.circuitcode;
            useCircuit.CircuitCode.ID = circuit.AgentID;
            useCircuit.CircuitCode.SessionID = circuit.SessionID;

            lock (clientCircuits)
            {
                if (!clientCircuits.ContainsKey(userEP))
                    clientCircuits.Add(userEP, useCircuit.CircuitCode.Code);
                else
                    m_log.Error("[CLIENT]: clientCircuits already contains entry for user " + useCircuit.CircuitCode.Code + ". NOT adding.");
            }

            // This data structure is synchronized, so we don't need the lock
            if (!clientCircuits_reverse.ContainsKey(useCircuit.CircuitCode.Code))
                clientCircuits_reverse.Add(useCircuit.CircuitCode.Code, userEP);
            else
                m_log.Error("[CLIENT]: clientCurcuits_reverse already contains entry for user " + useCircuit.CircuitCode.Code + ". NOT adding.");

            lock (proxyCircuits)
            {
                if (!proxyCircuits.ContainsKey(useCircuit.CircuitCode.Code))
                {
                    proxyCircuits.Add(useCircuit.CircuitCode.Code, proxyEP);
                }
                else
                {
                    // re-set proxy endpoint
                    proxyCircuits.Remove(useCircuit.CircuitCode.Code);
                    proxyCircuits.Add(useCircuit.CircuitCode.Code, proxyEP);
                }
            }

            m_packetServer.AddNewClient(userEP, useCircuit, m_assetCache, m_circuitManager, proxyEP);
        }
    }
}