/*
 * SPDX-License-Identifier: GPL-2.0-only
 *
 */

//
// Network topology
//
//           10Mb/s, 10ms       10Mb/s, 10ms
//       n0-----------------n1-----------------n2
//
//
// - Tracing of queues and packet receptions to file
//   "tcp-large-transfer.tr"
// - pcap traces also generated in the following files
//   "tcp-large-transfer-$n-$i.pcap" where n and i represent node and interface
// numbers respectively
//  Usage (e.g.): ./ns3 run tcp-large-transfer

#include "ns3/applications-module.h"
#include "ns3/core-module.h"
#include "ns3/internet-module.h"
#include "ns3/ipv4-global-routing-helper.h"
#include "ns3/network-module.h"
#include "ns3/point-to-point-module.h"

#include <fstream>
#include <iostream>
#include <string>

using namespace ns3;

NS_LOG_COMPONENT_DEFINE("TcpLargeTransfer");

/// The number of bytes to send in this simulation.
static const uint32_t totalTxBytes = 2000000;
/// The actual number of sent bytes.
static uint32_t currentTxBytes = 0;

// Perform series of 1040 byte writes (this is a multiple of 26 since
// we want to detect data splicing in the output stream)
/// Write size.
static const uint32_t writeSize = 1040;
/// Data to be written.
uint8_t data[writeSize];

// These are for starting the writing process, and handling the sending
// socket's notification upcalls (events).  These two together more or less
// implement a sending "Application", although not a proper ns3::Application
// subclass.

/**
 * Start a flow.
 *
 * \param localSocket The local (sending) socket.
 * \param servAddress The server address.
 * \param servPort The server port.
 */
void StartFlow(Ptr<Socket> localSocket, Ipv4Address servAddress, uint16_t servPort);

/**
 * Write to the buffer, filling it.
 *
 * \param localSocket The socket.
 * \param txSpace The number of bytes to write.
 */
void WriteUntilBufferFull(Ptr<Socket> localSocket, uint32_t txSpace);

/**
 * Congestion window tracker function.
 *
 * \param oldval Old value.
 * \param newval New value.
 */
static void
CwndTracer(uint32_t oldval, uint32_t newval)
{
    NS_LOG_INFO("Moving cwnd from " << oldval << " to " << newval);
}

int
main(int argc, char* argv[])
{
    // Users may find it convenient to turn on explicit debugging
    // for selected modules; the below lines suggest how to do this
    //  LogComponentEnable("TcpL4Protocol", LOG_LEVEL_ALL);
    //  LogComponentEnable("TcpSocketImpl", LOG_LEVEL_ALL);
    //  LogComponentEnable("PacketSink", LOG_LEVEL_ALL);
    //  LogComponentEnable("TcpLargeTransfer", LOG_LEVEL_ALL);

    CommandLine cmd(__FILE__);
    cmd.Parse(argc, argv);

    // initialize the tx buffer.
    for (uint32_t i = 0; i < writeSize; ++i)
    {
        char m = toascii(97 + i % 26);
        data[i] = m;
    }

    // Here, we will explicitly create three nodes.  The first container contains
    // nodes 0 and 1 from the diagram above, and the second one contains nodes
    // 1 and 2.  This reflects the channel connectivity, and will be used to
    // install the network interfaces and connect them with a channel.
    NodeContainer n0n1;
    n0n1.Create(2);

    NodeContainer n1n2;
    n1n2.Add(n0n1.Get(1));
    n1n2.Create(1);

    // We create the channels first without any IP addressing information
    // First make and configure the helper, so that it will put the appropriate
    // attributes on the network interfaces and channels we are about to install.
    PointToPointHelper p2p;
    p2p.SetDeviceAttribute("DataRate", DataRateValue(DataRate(10000000)));
    p2p.SetChannelAttribute("Delay", TimeValue(MilliSeconds(10)));

    // And then install devices and channels connecting our topology.
    NetDeviceContainer dev0 = p2p.Install(n0n1);
    NetDeviceContainer dev1 = p2p.Install(n1n2);

    // Now add ip/tcp stack to all nodes.
    InternetStackHelper internet;
    internet.InstallAll();

    // Later, we add IP addresses.
    Ipv4AddressHelper ipv4;
    ipv4.SetBase("10.1.3.0", "255.255.255.0");
    ipv4.Assign(dev0);
    ipv4.SetBase("10.1.2.0", "255.255.255.0");
    Ipv4InterfaceContainer ipInterfs = ipv4.Assign(dev1);

    // and setup ip routing tables to get total ip-level connectivity.
    Ipv4GlobalRoutingHelper::PopulateRoutingTables();

    ///////////////////////////////////////////////////////////////////////////
    // Simulation 1
    //
    // Send 2000000 bytes over a connection to server port 50000 at time 0
    // Should observe SYN exchange, a lot of data segments and ACKS, and FIN
    // exchange.  FIN exchange isn't quite compliant with TCP spec (see release
    // notes for more info)
    //
    ///////////////////////////////////////////////////////////////////////////

    uint16_t servPort = 50000;

    // Create a packet sink to receive these packets on n2...
    PacketSinkHelper sink("ns3::TcpSocketFactory",
                          InetSocketAddress(Ipv4Address::GetAny(), servPort));

    ApplicationContainer apps = sink.Install(n1n2.Get(1));
    apps.Start(Seconds(0.0));
    apps.Stop(Seconds(3.0));

    // Create a source to send packets from n0.  Instead of a full Application
    // and the helper APIs you might see in other example files, this example
    // will use sockets directly and register some socket callbacks as a sending
    // "Application".

    // Create and bind the socket...
    Ptr<Socket> localSocket = Socket::CreateSocket(n0n1.Get(0), TcpSocketFactory::GetTypeId());
    localSocket->Bind();

    // Trace changes to the congestion window
    Config::ConnectWithoutContext("/NodeList/0/$ns3::TcpL4Protocol/SocketList/0/CongestionWindow",
                                  MakeCallback(&CwndTracer));

    // ...and schedule the sending "Application"; This is similar to what an
    // ns3::Application subclass would do internally.
    Simulator::ScheduleNow(&StartFlow, localSocket, ipInterfs.GetAddress(1), servPort);

    // One can toggle the comment for the following line on or off to see the
    // effects of finite send buffer modelling.  One can also change the size of
    // said buffer.

    // localSocket->SetAttribute("SndBufSize", UintegerValue(4096));

    // Ask for ASCII and pcap traces of network traffic
    AsciiTraceHelper ascii;
    p2p.EnableAsciiAll(ascii.CreateFileStream("tcp-large-transfer.tr"));
    p2p.EnablePcapAll("tcp-large-transfer");

    // Finally, set up the simulator to run.  The 1000 second hard limit is a
    // failsafe in case some change above causes the simulation to never end
    Simulator::Stop(Seconds(1000));
    Simulator::Run();
    Simulator::Destroy();

    return 0;
}

//-----------------------------------------------------------------------------
//-----------------------------------------------------------------------------
//-----------------------------------------------------------------------------
// begin implementation of sending "Application"
void
StartFlow(Ptr<Socket> localSocket, Ipv4Address servAddress, uint16_t servPort)
{
    NS_LOG_LOGIC("Starting flow at time " << Simulator::Now().GetSeconds());
    localSocket->Connect(InetSocketAddress(servAddress, servPort)); // connect

    // tell the tcp implementation to call WriteUntilBufferFull again
    // if we blocked and new tx buffer space becomes available
    localSocket->SetSendCallback(MakeCallback(&WriteUntilBufferFull));
    WriteUntilBufferFull(localSocket, localSocket->GetTxAvailable());
}

void
WriteUntilBufferFull(Ptr<Socket> localSocket, uint32_t txSpace)
{
    while (currentTxBytes < totalTxBytes && localSocket->GetTxAvailable() > 0)
    {
        uint32_t left = totalTxBytes - currentTxBytes;
        uint32_t dataOffset = currentTxBytes % writeSize;
        uint32_t toWrite = writeSize - dataOffset;
        toWrite = std::min(toWrite, left);
        toWrite = std::min(toWrite, localSocket->GetTxAvailable());
        int amountSent = localSocket->Send(&data[dataOffset], toWrite, 0);
        if (amountSent < 0)
        {
            // we will be called again when new tx space becomes available.
            return;
        }
        currentTxBytes += amountSent;
    }
    if (currentTxBytes >= totalTxBytes)
    {
        localSocket->Close();
    }
}
