/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */

/*

 * Copyright (c) 2008 University of Washington

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License version 2 as

 * published by the Free Software Foundation;

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, write to the Free Software

 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

 *

 * Author: Tom Henderson <tomh@tomh.org>

 */

#include "ns3/log.h"

#include "ns3/command-line.h"

#include "ns3/ptr.h"

#include "ns3/config.h"

#include "ns3/uinteger.h"

#include "ns3/string.h"

#include "ns3/pointer.h"

#include "ns3/simulator.h"

#include "ns3/node.h"

#include "ns3/queue.h"

#include "ns3/drop-tail-queue.h"

#include "ns3/point-to-point-net-device.h"

using namespace ns3;

NS_LOG_COMPONENT_DEFINE ("AttributeValueSample");

//

// This is a basic example of how to use the attribute system to

// set and get a value in the underlying system; namely, an unsigned

// integer of the maximum number of packets in a queue

//

int 

main (int argc, char *argv[])

{

  LogComponentEnable ("AttributeValueSample", LOG_LEVEL_INFO);

  // By default, the MaxPackets attribute has a value of 100 packets

  // (this default can be observed in the function DropTailQueue::GetTypeId)

  // 

  // Here, we set it to 80 packets.  We could use one of two value types:

  // a string-based value or a UintegerValue value

  Config::SetDefault ("ns3::DropTailQueue::MaxPackets", StringValue ("80"));

  // The below function call is redundant

  Config::SetDefault ("ns3::DropTailQueue::MaxPackets", UintegerValue (80));

  // Allow the user to override any of the defaults and the above

  // SetDefaults() at run-time, via command-line arguments

  CommandLine cmd;

  cmd.Parse (argc, argv);

  // Now, we will create a few objects using the low-level API

  Ptr<Node> n0 = CreateObject<Node> ();

  Ptr<PointToPointNetDevice> net0 = CreateObject<PointToPointNetDevice> ();

  n0->AddDevice (net0);

  Ptr<Queue> q = CreateObject<DropTailQueue> ();

  net0->SetQueue(q);

  // At this point, we have created a single node (Node 0) and a 

  // single PointToPointNetDevice (NetDevice 0) and added a 

  // DropTailQueue to it.

  // Now, we can manipulate the MaxPackets value of the already 

  // instantiated DropTailQueue.  Here are various ways to do that.

  // We assume that a smart pointer (Ptr) to a relevant network device

  // is in hand; here, it is the net0 pointer. 

  // 1.  Pointer-based access

  //

  // One way to change the value is to access a pointer to the

  // underlying queue and modify its attribute.

  // 

  // First, we observe that we can get a pointer to the (base class)

  // queue via the PointToPointNetDevice attributes, where it is called

  // TxQueue 

  PointerValue ptr;

  net0->GetAttribute ("TxQueue", ptr);

  Ptr<Queue> txQueue = ptr.Get<Queue> ();

  // Using the GetObject function, we can perform a safe downcast

  // to a DropTailQueue, where MaxPackets is a member

  Ptr<DropTailQueue> dtq = txQueue->GetObject <DropTailQueue> ();

  NS_ASSERT (dtq);

  // Next, we can get the value of an attribute on this queue

  // We have introduced wrapper "Value" classes for the underlying

  // data types, similar to Java wrappers around these types, since

  // the attribute system stores values and not disparate types.

  // Here, the attribute value is assigned to a Uinteger, and

  // the Get() method on this value produces the (unwrapped) uint32_t.

  UintegerValue limit;

  dtq->GetAttribute ("MaxPackets", limit);

  NS_LOG_INFO ("1.  dtq limit: " << limit.Get () << " packets");

  // Note that the above downcast is not really needed; we could have

  // done the same using the Ptr<Queue> even though the attribute

  // is a member of the subclass

  txQueue->GetAttribute ("MaxPackets", limit);

  NS_LOG_INFO ("2.  txQueue limit: " << limit.Get () << " packets");

  // Now, let's set it to another value (60 packets)

  txQueue->SetAttribute("MaxPackets", UintegerValue (60));

  txQueue->GetAttribute ("MaxPackets", limit);

  NS_LOG_INFO ("3.  txQueue limit changed: " << limit.Get () << " packets");

  // 2.  Namespace-based access

  //

  // An alternative way to get at the attribute is to use the configuration

  // namespace.  Here, this attribute resides on a known path in this

  // namespace; this approach is useful if one doesn't have access to

  // the underlying pointers and would like to configure a specific

  // attribute with a single statement.  

  Config::Set ("/NodeList/0/DeviceList/0/TxQueue/MaxPackets", UintegerValue (25));

  txQueue->GetAttribute ("MaxPackets", limit); 

  NS_LOG_INFO ("4.  txQueue limit changed through namespace: " << 

               limit.Get () << " packets");

  // we could have also used wildcards to set this value for all nodes

  // and all net devices (which in this simple example has the same

  // effect as the previous Set())

  Config::Set ("/NodeList/*/DeviceList/*/TxQueue/MaxPackets", UintegerValue (15));

  txQueue->GetAttribute ("MaxPackets", limit); 

  NS_LOG_INFO ("5.  txQueue limit changed through wildcarded namespace: " << 

               limit.Get () << " packets");

  Simulator::Destroy ();

}