/* -*-  Mode: C++; c-file-style: "gnu"; indent-tabs-mode:nil; -*- */
/*
 * Copyright (c) 2006 Georgia Tech Research Corporation
 *
 * 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: George F. Riley<riley@ece.gatech.edu>
 */

#ifndef __APPLICATION_H__
#define __APPLICATION_H__

//
// \brief The base class for all ns3 applicationes
//
// Class Application is the base class for all ns3 applications.
// Applications are associated with individual nodes, and are created
// using the AddApplication method in the ApplicationManager capability.
// 
// Conceptually, an application has zero or more Socket
// objects associated with it, that are created using the Socket
// creation API of the Kernel capability.  The Socket object
// API is modeled after the
// well-known BSD sockets interface, although it is somewhat 
// simplified for use with ns3.  Further, any socket call that
// would normally "block" in normal sockets will return immediately
// in ns3.  A set of "upcalls" are defined that will be called when
// the previous blocking call would normally exit.  THis is documented
// in more detail Socket class in socket.h.
// 
// There is a second application class in ns3, called "ThreadedApplication"
// that implements a true sockets interface, which should be used
// when porting existing sockets code to ns3.  The true
// sockets approach is significantly
// less memory--efficient using private stacks for each defined application,
// so that approach should be used with care.  The design and implementation
// of the ThreadedApplication are still being discussed.

#include "ns3/event-id.h"
#include "ns3/nstime.h"
#include "ns3/object.h"
#include "ns3/ptr.h"
#include "ns3/node.h"

namespace ns3 {

class Node;
class RandomVariable;

/**
 * \brief a model for userspace applications.
 */
class Application : public Object
{
public:
  Application(Ptr<Node>);
  virtual ~Application();
  
  /**
   * \brief Specify application start time
   * Applications start at various times in the simulation scenario.
   * The Start method specifies when the application should be
   * started.  The application subclasses should override the
   * private "StartApplication" method defined below, which is called at the
   * time specified, to cause the application to begin.
   * \param startTime Start time for this application, absolute time,
   *        relative to the start of the simulation.
   */
  void Start(const Time& startTime);

  /** 
   * \brief Same as above, but uses a random variable for start time
   * The random variable returns the desired start time in units of
   * Seconds.
   * \param startVariable the random variable to use to pick
   *        the real start time as an absolute time, relative to
   *        the start of the simulation.
   */
  void Start(const RandomVariable& startVariable);
  
  /**
   * \brief Specify application stop time
   * Once an application has started, it is sometimes useful
   * to stop the application.  The Stop method specifies when an
   * application is to stop.  The application subclasses should override
   * the private StopApplication method defined below, to cause the application
   * to stop.
   * \param stopTime Stop time for this application, relative to the
   *        start of the simulation.
   */
  void Stop(const Time& stopTime);

  /**
   * \brief Same as above, but uses a random variable for stop time
   * The random variable returns the desired stop time in units of
   * Seconds.
   * \param stopVariable the random variable to use to pick
   *        the real stop time, relative to the start of the simulation.
   */
  void Stop(const RandomVariable& stopVariable);

  /**
   * \returns the Node to which this Application object is attached.
   */
  Ptr<Node> GetNode() const;
  
private:
  // Members
  Ptr<Node>       m_node;      // All applications have an associated node
  EventId         m_startEvent;// Event identifier for start event
  EventId         m_stopEvent; // Event identifier for the stop event

private:
  /**
   * \brief Application specific startup code
   * The StartApplication method is called at the start time specifed by Start
   * This method should be overridden by all or most application
   * subclasses.
   */
  virtual void StartApplication (void);

  /**
   * \brief Application specific shutdown code
   * The StopApplication method is called at the stop time specifed by Stop
   * This method should be overridden by all or most application
   * subclasses.
   */
  virtual void StopApplication (void);
protected:
  virtual void DoDispose (void);
private:
  // Helpers
  void ScheduleStart (const Time &time);
  void ScheduleStop (const Time &time);
};

} //namespace ns3
#endif