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

# Network topology
#
#       n0    n1   n2   n3
#       |     |    |    |
#       =================
#              LAN
#
# - UDP flows from n0 to n1 and back
# - DropTail queues
# - Tracing of queues and packet receptions to file "udp-echo.tr"

try:
    from ns import ns
except ModuleNotFoundError:
    raise SystemExit(
        "Error: ns3 Python module not found;"
        " Python bindings may not be enabled"
        " or your PYTHONPATH might not be properly configured"
    )


def main(argv):
    #
    # Allow the user to override any of the defaults and the above Bind() at
    # run-time, via command-line arguments
    #
    cmd = ns.CommandLine()
    cmd.Parse(argv)

    #
    # But since this is a realtime script, don't allow the user to mess with
    # that.
    #
    ns.GlobalValue.Bind("SimulatorImplementationType", ns.StringValue("ns3::RealtimeSimulatorImpl"))

    #
    # Explicitly create the nodes required by the topology (shown above).
    #
    print("Create nodes.")
    n = ns.NodeContainer()
    n.Create(4)

    internet = ns.InternetStackHelper()
    internet.Install(n)

    #
    # Explicitly create the channels required by the topology (shown above).
    #
    print("Create channels.")
    csma = ns.CsmaHelper()
    csma.SetChannelAttribute("DataRate", ns.DataRateValue(ns.DataRate(5000000)))
    csma.SetChannelAttribute("Delay", ns.TimeValue(ns.MilliSeconds(2)))
    csma.SetDeviceAttribute("Mtu", ns.UintegerValue(1400))
    d = csma.Install(n)

    #
    # We've got the "hardware" in place.  Now we need to add IP addresses.
    #
    print("Assign IP Addresses.")
    ipv4 = ns.Ipv4AddressHelper()
    ipv4.SetBase(ns.Ipv4Address("10.1.1.0"), ns.Ipv4Mask("255.255.255.0"))
    i = ipv4.Assign(d)

    print("Create Applications.")

    #
    # Create a UdpEchoServer application on node one.
    #
    port = 9  # well-known echo port number
    server = ns.UdpEchoServerHelper(port)
    apps = server.Install(n.Get(1))
    apps.Start(ns.Seconds(1.0))
    apps.Stop(ns.Seconds(10.0))

    #
    # Create a UdpEchoClient application to send UDP datagrams from node zero to
    # node one.
    #
    packetSize = 1024
    maxPacketCount = 500
    interPacketInterval = ns.Seconds(0.01)
    client = ns.UdpEchoClientHelper(i.GetAddress(1).ConvertTo(), port)
    client.SetAttribute("MaxPackets", ns.UintegerValue(maxPacketCount))
    client.SetAttribute("Interval", ns.TimeValue(interPacketInterval))
    client.SetAttribute("PacketSize", ns.UintegerValue(packetSize))
    apps = client.Install(n.Get(0))
    apps.Start(ns.Seconds(2.0))
    apps.Stop(ns.Seconds(10.0))

    ascii = ns.AsciiTraceHelper()
    csma.EnableAsciiAll(ascii.CreateFileStream("realtime-udp-echo.tr"))
    csma.EnablePcapAll("realtime-udp-echo", False)

    #
    # Now, do the actual simulation.
    #
    print("Run Simulation.")
    ns.Simulator.Stop(ns.Seconds(10))
    ns.Simulator.Run()
    ns.Simulator.Destroy()
    print("Done.")


if __name__ == "__main__":
    import sys

    main(sys.argv)