/* Copyright (C) 2012-2016 Tal Aloni <tal.aloni.il@gmail.com>. All rights reserved.
 * 
 * You can redistribute this program and/or modify it under the terms of
 * the GNU Lesser Public License as published by the Free Software Foundation,
 * either version 3 of the License, or (at your option) any later version.
 */
using System;
using System.Collections.Generic;
using System.IO;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.Threading;
using Utilities;

namespace ISCSI.Server
{
    public delegate ushort GetNextTSIH();

    public class ISCSIServer // Server may serve more than one target
    {
        public const int DefaultPort = 3260;

        // Offered Session Parameters:
        public static bool OfferedInitialR2T = true;
        public static bool OfferedImmediateData = true;
        public static int OfferedMaxBurstLength = SessionParameters.DefaultMaxBurstLength;
        public static int OfferedFirstBurstLength = SessionParameters.DefaultFirstBurstLength;
        public static int OfferedDefaultTime2Wait = 0;
        public static int OfferedDefaultTime2Retain = 20;
        public static int OfferedMaxOutstandingR2T = 1;
        public static bool OfferedDataPDUInOrder = true;
        public static bool OfferedDataSequenceInOrder = true;
        public static int OfferedErrorRecoveryLevel = 0;
        public static int OfferedMaxConnections = 1;

        private List<ISCSITarget> m_targets;
        private int m_port;
        private ushort m_nextTSIH = 1; // Next Target Session Identifying Handle

        private Socket m_listenerSocket;
        private bool m_listening;
        public ConnectionManager m_connectionManager = new ConnectionManager();

        public event EventHandler<LogEntry> OnLogEntry;
        
        public ISCSIServer(List<ISCSITarget> targets) : this(targets, DefaultPort)
        { }

        public ISCSIServer(List<ISCSITarget> targets, int port) : this(targets, port, String.Empty)
        { }

        /// <summary>
        /// Server needs to be started with Start()
        /// </summary>
        public ISCSIServer(List<ISCSITarget> targets, int port, string logFilePath)
        {
            m_port = port;
            m_targets = targets;
        }

        public void Start()
        {
            if (!m_listening)
            {
                Log(Severity.Information, "Starting Server");
                m_listening = true;

                m_listenerSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
                m_listenerSocket.Bind(new IPEndPoint(IPAddress.Any, m_port));
                m_listenerSocket.Listen(1000);
                m_listenerSocket.BeginAccept(ConnectRequestCallback, m_listenerSocket);
            }
        }

        // This method accepts new connections
        private void ConnectRequestCallback(IAsyncResult ar)
        {
            Socket listenerSocket = (Socket)ar.AsyncState;

            Socket clientSocket;
            try
            {
                clientSocket = listenerSocket.EndAccept(ar);
            }
            catch (ObjectDisposedException)
            {
                return;
            }
            catch (SocketException)
            {
                return;
            }

            Log(Severity.Information, "New connection has been accepted");

            ConnectionState state = new ConnectionState();
            state.ConnectionParameters.InitiatorEndPoint = clientSocket.RemoteEndPoint as IPEndPoint;
            state.ReceiveBuffer = new byte[ConnectionState.ReceiveBufferSize];
            // Disable the Nagle Algorithm for this tcp socket:
            clientSocket.NoDelay = true;
            state.ClientSocket = clientSocket;
            Thread senderThread = new Thread(delegate()
            {
                ProcessSendQueue(state);
            });
            senderThread.IsBackground = true;
            senderThread.Start();

            try
            {
                clientSocket.BeginReceive(state.ReceiveBuffer, 0, ConnectionState.ReceiveBufferSize, 0, ReceiveCallback, state);
            }
            catch (ObjectDisposedException)
            {
                Log(Severity.Debug, "[OnConnectRequest] BeginReceive ObjectDisposedException");
            }
            catch (SocketException ex)
            {
                Log(Severity.Debug, "[OnConnectRequest] BeginReceive SocketException: {0}", ex.Message);
            }
            m_listenerSocket.BeginAccept(ConnectRequestCallback, m_listenerSocket);
        }

        public void Stop()
        {
            Log(Severity.Information, "Stopping Server");
            m_listening = false;
            SocketUtils.ReleaseSocket(m_listenerSocket);
        }

        private void ReceiveCallback(IAsyncResult result)
        {
            if (!m_listening)
            {
                return;
            }

            ConnectionState state = (ConnectionState)result.AsyncState;
            Socket clientSocket = state.ClientSocket;
            if (!clientSocket.Connected)
            {
                return;
            }

            int numberOfBytesReceived;
            try
            {
                numberOfBytesReceived = clientSocket.EndReceive(result);
            }
            catch (ObjectDisposedException)
            {
                Log(Severity.Debug, "[ReceiveCallback] EndReceive ObjectDisposedException");
                return;
            }
            catch (SocketException ex)
            {
                Log(Severity.Debug, "[ReceiveCallback] EndReceive SocketException: {0}", ex.Message);
                return;
            }

            if (numberOfBytesReceived == 0)
            {
                // The other side has closed the connection
                clientSocket.Close();
                Log(Severity.Verbose, "The initiator has closed the connection");
                // Wait for pending I/O to complete.
                state.RunningSCSICommands.WaitUntilZero();
                state.SendQueue.Stop();
                m_connectionManager.RemoveConnection(state);
                return;
            }

            byte[] currentBuffer = ByteReader.ReadBytes(state.ReceiveBuffer, 0, numberOfBytesReceived);
            ProcessCurrentBuffer(currentBuffer, state);

            try
            {
                clientSocket.BeginReceive(state.ReceiveBuffer, 0, ConnectionState.ReceiveBufferSize, 0, ReceiveCallback, state);
            }
            catch (ObjectDisposedException)
            {
                Log(Severity.Debug, "[ReceiveCallback] BeginReceive ObjectDisposedException");
            }
            catch (SocketException ex)
            {
                Log(Severity.Debug, "[ReceiveCallback] BeginReceive SocketException: {0}", ex.Message);
            }
        }

        private void ProcessCurrentBuffer(byte[] currentBuffer, ConnectionState state)
        {
            Socket clientSocket = state.ClientSocket;

            if (state.ConnectionBuffer.Length == 0)
            {
                state.ConnectionBuffer = currentBuffer;
            }
            else
            {
                state.ConnectionBuffer = ByteUtils.Concatenate(state.ConnectionBuffer, currentBuffer);
            }

            // we now have all PDU bytes received so far in state.ConnectionBuffer
            int bytesLeftInBuffer = state.ConnectionBuffer.Length;

            while (bytesLeftInBuffer >= 8)
            {
                int bufferOffset = state.ConnectionBuffer.Length - bytesLeftInBuffer;
                int pduLength = ISCSIPDU.GetPDULength(state.ConnectionBuffer, bufferOffset);
                if (pduLength > bytesLeftInBuffer)
                {
                    Log(Severity.Debug, "[{0}][ProcessCurrentBuffer] Bytes left in receive buffer: {1}", state.ConnectionIdentifier, bytesLeftInBuffer);
                    break;
                }
                else
                {
                    byte[] pduBytes = ByteReader.ReadBytes(state.ConnectionBuffer, bufferOffset, pduLength);
                    bytesLeftInBuffer -= pduLength;
                    ISCSIPDU pdu = null;
                    try
                    {
                        pdu = ISCSIPDU.GetPDU(pduBytes);
                    }
                    catch (Exception ex)
                    {
                        Log(Severity.Error, "[{0}] Failed to read PDU (Exception: {1})", state.ConnectionIdentifier, ex.Message);
                        RejectPDU reject = new RejectPDU();
                        reject.Reason = RejectReason.InvalidPDUField;
                        reject.Data = ByteReader.ReadBytes(pduBytes, 0, 48);

                        state.SendQueue.Enqueue(reject);
                    }

                    if (pdu != null)
                    {
                        if (pdu.GetType() == typeof(ISCSIPDU))
                        {
                            Log(Severity.Error, "[{0}][ProcessCurrentBuffer] Unsupported PDU (0x{1})", state.ConnectionIdentifier, pdu.OpCode.ToString("X"));
                            // Unsupported PDU
                            RejectPDU reject = new RejectPDU();
                            reject.InitiatorTaskTag = pdu.InitiatorTaskTag;
                            reject.Reason = RejectReason.CommandNotSupported;
                            reject.Data = ByteReader.ReadBytes(pduBytes, 0, 48);
                            state.SendQueue.Enqueue(reject);
                        }
                        else
                        {
                            ProcessPDU(pdu, state);
                        }
                    }
                    
                    if (!clientSocket.Connected)
                    {
                        // Do not continue to process the buffer if the other side closed the connection
                        if (bytesLeftInBuffer > 0)
                        {
                            Log(Severity.Debug, "[{0}] Buffer processing aborted, bytes left in receive buffer: {1}", state.ConnectionIdentifier, bytesLeftInBuffer);
                        }
                        return;
                    }
                }
            }

            if (bytesLeftInBuffer > 0)
            {
                state.ConnectionBuffer = ByteReader.ReadBytes(state.ConnectionBuffer, state.ConnectionBuffer.Length - bytesLeftInBuffer, bytesLeftInBuffer);
            }
            else
            {
                state.ConnectionBuffer = new byte[0];
            }
        }

        private void ProcessPDU(ISCSIPDU pdu, ConnectionState state)
        {
            Socket clientSocket = state.ClientSocket;
            
            uint? cmdSN = PDUHelper.GetCmdSN(pdu);
            Log(Severity.Trace, "Entering ProcessPDU");
            Log(Severity.Verbose, "[{0}] Received PDU from initiator, Operation: {1}, Size: {2}, CmdSN: {3}", state.ConnectionIdentifier, (ISCSIOpCodeName)pdu.OpCode, pdu.Length, cmdSN);
            // RFC 3720: On any connection, the iSCSI initiator MUST send the commands in increasing order of CmdSN,
            // except for commands that are retransmitted due to digest error recovery and connection recovery.
            if (cmdSN.HasValue)
            {
                if (state.SessionParameters.CommandNumberingStarted)
                {
                    if (cmdSN != state.SessionParameters.ExpCmdSN)
                    {
                        Log(Severity.Error, "[{0}] CmdSN outside of expected range", state.ConnectionIdentifier);
                        // We ignore this PDU
                        Log(Severity.Trace, "Leaving ProcessPDU");
                        return;
                    }
                }
                else
                {
                    state.SessionParameters.ExpCmdSN = cmdSN.Value;
                    state.SessionParameters.CommandNumberingStarted = true;
                }

                if (pdu is LogoutRequestPDU || pdu is TextRequestPDU || pdu is SCSICommandPDU || pdu is RejectPDU)
                {
                    if (!pdu.ImmediateDelivery)
                    {
                        state.SessionParameters.ExpCmdSN++;
                    }
                }
            }

            if (!state.SessionParameters.IsFullFeaturePhase)
            {
                if (pdu is LoginRequestPDU)
                {
                    LoginRequestPDU request = (LoginRequestPDU)pdu;
                    Log(Severity.Verbose, "[{0}] Login Request, current stage: {1}, next stage: {2}, parameters: {3}", state.ConnectionIdentifier, request.CurrentStage, request.NextStage, KeyValuePairUtils.ToString(request.LoginParameters));
                    if (request.TSIH != 0)
                    {
                        // RFC 3720: A Login Request with a non-zero TSIH and a CID equal to that of an existing
                        // connection implies a logout of the connection followed by a Login
                        ConnectionState existingConnection = m_connectionManager.FindConnection(request.ISID, request.TSIH, request.CID);
                        if (existingConnection != null)
                        {
                            // Perform implicit logout
                            Log(Severity.Verbose, "[{0}] Initiating implicit logout", state.ConnectionIdentifier);
                            // Wait for pending I/O to complete.
                            existingConnection.RunningSCSICommands.WaitUntilZero();
                            SocketUtils.ReleaseSocket(existingConnection.ClientSocket);
                            existingConnection.SendQueue.Stop();
                            m_connectionManager.RemoveConnection(existingConnection);
                            Log(Severity.Verbose, "[{0}] Implicit logout completed", state.ConnectionIdentifier);
                        }
                    }
                    LoginResponsePDU response = ServerResponseHelper.GetLoginResponsePDU(request, m_targets, state.SessionParameters, state.ConnectionParameters, ref state.Target, GetNextTSIH);
                    if (state.SessionParameters.IsFullFeaturePhase)
                    {
                        state.SessionParameters.ISID = request.ISID;
                        state.ConnectionParameters.CID = request.CID;
                        m_connectionManager.AddConnection(state);
                    }
                    Log(Severity.Verbose, "[{0}] Login Response parameters: {1}", state.ConnectionIdentifier, KeyValuePairUtils.ToString(response.LoginParameters));
                    state.SendQueue.Enqueue(response);
                }
                else
                {
                    // Before the Full Feature Phase is established, only Login Request and Login Response PDUs are allowed.
                    Log(Severity.Error, "[{0}] Improper command during login phase, OpCode: 0x{1}", state.ConnectionIdentifier, pdu.OpCode.ToString("x"));
                    if (state.SessionParameters.TSIH == 0)
                    {
                        // A target receiving any PDU except a Login request before the Login phase is started MUST
                        // immediately terminate the connection on which the PDU was received.
                        clientSocket.Close();
                    }
                    else
                    {
                        // Once the Login phase has started, if the target receives any PDU except a Login request,
                        // it MUST send a Login reject (with Status "invalid during login") and then disconnect.
                        LoginResponsePDU loginResponse = new LoginResponsePDU();
                        loginResponse.TSIH = state.SessionParameters.TSIH;
                        loginResponse.Status = LoginResponseStatusName.InvalidDuringLogon;
                        state.SendQueue.Enqueue(loginResponse);
                    }
                }
            }
            else // Logged in
            {
                if (pdu is TextRequestPDU)
                {
                    TextRequestPDU request = (TextRequestPDU)pdu;
                    TextResponsePDU response = ServerResponseHelper.GetTextResponsePDU(request, m_targets);
                    state.SendQueue.Enqueue(response);
                }
                else if (pdu is LogoutRequestPDU)
                {
                    Log(Severity.Verbose, "[{0}] Logour Request", state.ConnectionIdentifier);
                    LogoutRequestPDU request = (LogoutRequestPDU)pdu;
                    if (state.SessionParameters.IsDiscovery && request.ReasonCode != LogoutReasonCode.CloseTheSession)
                    {
                        // RFC 3720: Discovery-session: The target MUST ONLY accept [..] logout request with the reason "close the session"
                        RejectPDU reject = new RejectPDU();
                        reject.Reason = RejectReason.ProtocolError;
                        reject.Data = ByteReader.ReadBytes(pdu.GetBytes(), 0, 48);
                        state.SendQueue.Enqueue(reject);
                    }
                    else
                    {
                        List<ConnectionState> connectionsToClose = new List<ConnectionState>();
                        if (request.ReasonCode == LogoutReasonCode.CloseTheSession)
                        {
                            connectionsToClose = m_connectionManager.GetSessionConnections(state.SessionParameters.ISID, state.SessionParameters.TSIH);
                        }
                        else
                        {
                            // RFC 3720: A Logout for a CID may be performed on a different transport connection when the TCP connection for the CID has already been terminated.
                            ConnectionState existingConnection = m_connectionManager.FindConnection(state.SessionParameters.ISID, state.SessionParameters.TSIH, request.CID);
                            if (existingConnection != null && existingConnection != state)
                            {
                                connectionsToClose.Add(existingConnection);
                            }
                            connectionsToClose.Add(state);
                        }

                        foreach (ConnectionState connection in connectionsToClose)
                        {
                            // Wait for pending I/O to complete.
                            connection.RunningSCSICommands.WaitUntilZero();
                            if (connection != state)
                            {
                                SocketUtils.ReleaseSocket(connection.ClientSocket);
                            }
                            m_connectionManager.RemoveConnection(connection);
                        }
                        LogoutResponsePDU response = ServerResponseHelper.GetLogoutResponsePDU(request);
                        state.SendQueue.Enqueue(response);
                        // connection will be closed after a LogoutResponsePDU has been sent.
                    }
                }
                else if (state.SessionParameters.IsDiscovery)
                {
                    // The target MUST ONLY accept text requests with the SendTargets key and a logout
                    // request with the reason "close the session".  All other requests MUST be rejected.
                    Log(Severity.Error, "[{0}] Improper command during discovery session, OpCode: 0x{1}", state.ConnectionIdentifier, pdu.OpCode.ToString("x"));
                    RejectPDU reject = new RejectPDU();
                    reject.Reason = RejectReason.ProtocolError;
                    reject.Data = ByteReader.ReadBytes(pdu.GetBytes(), 0, 48);

                    state.SendQueue.Enqueue(reject);
                }
                else if (pdu is NOPOutPDU)
                {
                    NOPOutPDU request = (NOPOutPDU)pdu;
                    if (request.InitiatorTaskTag != 0xFFFFFFFF)
                    {
                        NOPInPDU response = ServerResponseHelper.GetNOPResponsePDU(request);
                        state.SendQueue.Enqueue(response);
                    }
                }
                else if (pdu is SCSIDataOutPDU || pdu is SCSICommandPDU)
                {
                    // RFC 3720: the iSCSI target layer MUST deliver the commands for execution (to the SCSI execution engine) in the order specified by CmdSN.
                    // e.g. read requests should not be executed while previous write request data is being received (via R2T)
                    List<SCSICommandPDU> commandsToExecute = null;
                    List<ReadyToTransferPDU> readyToTransferPDUs = new List<ReadyToTransferPDU>();
                    if (pdu is SCSIDataOutPDU)
                    {
                        SCSIDataOutPDU request = (SCSIDataOutPDU)pdu;
                        Log(Severity.Debug, "[{0}] SCSIDataOutPDU: Target transfer tag: {1}, LUN: {2}, Buffer offset: {3}, Data segment length: {4}, DataSN: {5}, Final: {6}", state.ConnectionIdentifier, request.TargetTransferTag, (ushort)request.LUN, request.BufferOffset, request.DataSegmentLength, request.DataSN, request.Final);
                        try
                        {
                            readyToTransferPDUs = TargetResponseHelper.GetReadyToTransferPDUs(request, state.Target, state.SessionParameters, state.ConnectionParameters, out commandsToExecute);
                        }
                        catch (InvalidTargetTransferTagException ex)
                        {
                            Log(Severity.Error, "[{0}] Invalid TargetTransferTag: {1}", state.ConnectionIdentifier, ex.TargetTransferTag);
                            RejectPDU reject = new RejectPDU();
                            reject.InitiatorTaskTag = request.InitiatorTaskTag;
                            reject.Reason = RejectReason.InvalidPDUField;
                            reject.Data = ByteReader.ReadBytes(request.GetBytes(), 0, 48);
                            state.SendQueue.Enqueue(reject);
                        }
                    }
                    else
                    {
                        SCSICommandPDU command = (SCSICommandPDU)pdu;
                        Log(Severity.Debug, "[{0}] SCSICommandPDU: CmdSN: {1}, LUN: {2}, Data segment length: {3}, Expected Data Transfer Length: {4}, Final: {5}", state.ConnectionIdentifier, command.CmdSN, (ushort)command.LUN, command.DataSegmentLength, command.ExpectedDataTransferLength, command.Final);
                        readyToTransferPDUs = TargetResponseHelper.GetReadyToTransferPDUs(command, state.Target, state.SessionParameters, state.ConnectionParameters, out commandsToExecute);
                    }
                    foreach (ReadyToTransferPDU readyToTransferPDU in readyToTransferPDUs)
                    {
                        state.SendQueue.Enqueue(readyToTransferPDU);
                    }
                    if (commandsToExecute != null)
                    {
                        state.RunningSCSICommands.Add(commandsToExecute.Count);
                    }
                    List<ISCSIPDU> responseList = new List<ISCSIPDU>();
                    foreach(SCSICommandPDU command in commandsToExecute)
                    {
                        Log(Severity.Debug, "[{0}] Executing command: CmdSN: {1}", state.ConnectionIdentifier, command.CmdSN);
                        List<ISCSIPDU> commandResponseList = TargetResponseHelper.GetSCSICommandResponse(command, state.Target, state.SessionParameters, state.ConnectionParameters);
                        state.RunningSCSICommands.Decrement();
                        responseList.AddRange(commandResponseList);
                    }
                    state.SendQueue.Enqueue(responseList);
                }
                else if (pdu is LoginRequestPDU)
                {
                    Log(Severity.Error, "[{0}] Protocol Error (Login request during full feature phase)", state.ConnectionIdentifier);
                    // RFC 3720: Login requests and responses MUST be used exclusively during Login.
                    // On any connection, the login phase MUST immediately follow TCP connection establishment and
                    // a subsequent Login Phase MUST NOT occur before tearing down a connection
                    RejectPDU reject = new RejectPDU();
                    reject.Reason = RejectReason.ProtocolError;
                    reject.Data = ByteReader.ReadBytes(pdu.GetBytes(), 0, 48);

                    state.SendQueue.Enqueue(reject);
                }
                else
                {
                    Log(Severity.Error, "[{0}] Unsupported command, OpCode: 0x{1}", state.ConnectionIdentifier, pdu.OpCode.ToString("x"));
                    RejectPDU reject = new RejectPDU();
                    reject.Reason = RejectReason.CommandNotSupported;
                    reject.Data = ByteReader.ReadBytes(pdu.GetBytes(), 0, 48);

                    state.SendQueue.Enqueue(reject);
                }
            }
            Log(Severity.Trace, "Leaving ProcessPDU");
        }

        private void ProcessSendQueue(ConnectionState state)
        {
            while (true)
            {
                Log(Severity.Trace, "Entering ProcessSendQueue");
                ISCSIPDU response;
                bool stopped = !state.SendQueue.TryDequeue(out response);
                if (stopped)
                {
                    return;
                }
                Socket clientSocket = state.ClientSocket;
                PDUHelper.SetStatSN(response, state.ConnectionParameters.StatSN);
                PDUHelper.SetExpCmdSN(response, state.SessionParameters.ExpCmdSN, state.SessionParameters.ExpCmdSN + state.SessionParameters.CommandQueueSize);
                if (response is SCSIResponsePDU ||
                    response is LoginResponsePDU ||
                    response is TextResponsePDU ||
                    (response is SCSIDataInPDU && ((SCSIDataInPDU)response).StatusPresent) ||
                    response is RejectPDU)
                {
                    state.ConnectionParameters.StatSN++;
                }
                try
                {
                    clientSocket.Send(response.GetBytes());
                    Log(Severity.Verbose, "[{0}] Sent response to initator, Operation: {1}, Size: {2}", state.ConnectionIdentifier, response.OpCode, response.Length);
                    if (response is LogoutResponsePDU)
                    {
                        clientSocket.Close(); // We can close the connection now
                        Log(Severity.Trace, "Leaving ProcessSendQueue");
                        return;
                    }
                    else if (response is LoginResponsePDU)
                    {
                        if (((LoginResponsePDU)response).Status == LoginResponseStatusName.InvalidDuringLogon)
                        {
                            clientSocket.Close(); // We can close the connection now
                            Log(Severity.Trace, "Leaving ProcessSendQueue");
                            return;                            
                        }
                    }
                }
                catch (SocketException ex)
                {
                    Log(Severity.Verbose, "[{0}] Failed to send response to initator. Operation: {1}, Size: {2}, SocketException: {3}", state.ConnectionIdentifier, response.OpCode, response.Length, ex.Message);
                    Log(Severity.Trace, "Leaving ProcessSendQueue");
                    return;
                }
                catch (ObjectDisposedException)
                {
                    Log(Severity.Verbose, "[{0}] Failed to send response to initator. Operation: {1}, Size: {2}. ObjectDisposedException", state.ConnectionIdentifier, response.OpCode, response.Length);
                    Log(Severity.Trace, "Leaving ProcessSendQueue");
                    return;
                }
            }
        }

        public void Log(Severity severity, string message)
        {
            // To be thread-safe we must capture the delegate reference first
            EventHandler<LogEntry> handler = OnLogEntry;
            if (handler != null)
            {
                handler(this, new LogEntry(DateTime.Now, severity, "iSCSI Server", message));
            }
        }

        public void Log(Severity severity, string message, params object[] args)
        {
            Log(severity, String.Format(message, args));
        }

        public ushort GetNextTSIH()
        {
            // The iSCSI Target selects a non-zero value for the TSIH at
            // session creation (when an initiator presents a 0 value at Login).
            // After being selected, the same TSIH value MUST be used whenever the
            // initiator or target refers to the session and a TSIH is required
            ushort nextTSIH = m_nextTSIH;
            m_nextTSIH++;
            if (m_nextTSIH == 0)
            {
                m_nextTSIH++;
            }
            return nextTSIH;
        }
    }
}