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

/*

 * Copyright (c) 2005 INRIA

 *

 * 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: Mathieu Lacage <mathieu.lacage@sophia.inria.fr>

 */

#ifndef SCHEDULER_H

#define SCHEDULER_H

#include <stdint.h>

#include "ns3/object.h"

namespace ns3 {

class EventImpl;

/**

 * \ingroup simulator

 * \defgroup scheduler Scheduler

 */

/**

 * \ingroup scheduler

 * \brief Maintain the event list

 *

 * This base class specifies the interface used to maintain the 

 * event list. If you want to provide a new event list scheduler, 

 * you need to create a subclass of this base class and implement 

 * all the pure virtual methods defined here.

 *

 * The only tricky aspect of this API is the memory management of

 * the EventImpl pointer which is a member of the Event data structure.

 * The lifetime of this pointer is assumed to always be longer than

 * the lifetime of the Scheduler class which means that the caller

 * is responsible for ensuring that this invariant holds through

 * calling EventImpl::Ref and EventImpl::Unref at the right time.

 * Typically, ::Ref is called before Insert and ::Unref is called

 * after a call to one of the Remove methods.

 */

class Scheduler : public Object

{

 public:

  static TypeId GetTypeId (void);

  struct EventKey {

      uint64_t m_ts;

      uint32_t m_uid;

  };

  struct Event {

    EventImpl *impl;

    EventKey key;

  };

  virtual ~Scheduler () = 0;

  /**

   * \param ev event to store in the event list

   */

  virtual void Insert (const Event &ev) = 0;

  /**

   * \returns true if the event list is empty and false otherwise.

   */

  virtual bool IsEmpty (void) const = 0;

  /**

   * \returns a pointer to the next earliest event. The caller

   *      takes ownership of the returned pointer.

   *

   * This method cannot be invoked if the list is empty.

   */

  virtual Event PeekNext (void) const = 0;

  /**

   * This method cannot be invoked if the list is empty.

   * Remove the next earliest event from the event list.

   */

  virtual Event RemoveNext (void) = 0;

  /**

   *

   * This methods cannot be invoked if the list is empty.

   */

  virtual void Remove (const Event &ev) = 0;

};

/* Note the invariants which this function must provide:

 * - irreflexibility: f (x,x) is false)

 * - antisymmetry: f(x,y) = !f(y,x)

 * - transitivity: f(x,y) and f(y,z) => f(x,z)

 */

inline bool operator < (const Scheduler::EventKey &a, const Scheduler::EventKey &b)

{

  if (a.m_ts < b.m_ts)

    {

      return true;

    }

  else if (a.m_ts == b.m_ts &&

           a.m_uid < b.m_uid)

    {

      return true;

    }

  else

    {

      return false;

    }

}

inline bool operator < (const Scheduler::Event &a, const Scheduler::Event &b)

{

  return a.key < b.key;

}

} // namespace ns3

#endif /* SCHEDULER_H */