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

#include "ns3/nstime.h"

#include "ns3/event-id.h"

#include <vector>

namespace ns3 {

/**

 * \brief keep track of the state needed for a single DCF 

 * function.

 *

 * Multiple instances of a DcfState can be registered in a single

 * DcfManager to implement 802.11e-style relative QoS.

 * DcfState::SetAifsn and DcfState::SetCwBounds allow the user to 

 * control the relative QoS differentiation.

 */

class DcfState

{

public:

  DcfState ();

  virtual ~DcfState ();

  /**

   * \param aifsn the number of slots which make up an AIFS for a specific DCF.

   *        a DIFS corresponds to an AIFSN = 2.

   *

   * Calling this method after DcfManager::Add has been called is not recommended.

   */

  void SetAifsn (uint32_t aifsn);

  /**

   * Update the value of the CW variable to take into account

   * a transmission success or a transmission abort (stop transmission

   * of a packet after the maximum number of retransmissions has been

   * reached). By default, this resets the CW variable to minCW.

   */

  void ResetCw (void);

  /**

   * Update the value of the CW variable to take into account

   * a transmission failure. By default, this triggers a doubling

   * of CW (capped by maxCW).

   */

  void UpdateFailedCw (void);

  /**

   * \param nSlots the number of slots of the backoff.

   *

   * Start a backoff by initializing the backoff counter to the number of

   * slots specified.

   */

  void StartBackoffNow (uint32_t nSlots);

  /**

   * \returns the current value of the CW variable. The initial value is

   * minCW.

   */

  uint32_t GetCw (void) const;

  /**

   * \returns true if access has been requested for this DcfState and

   *          has not been granted already, false otherwise.

   */

  bool IsAccessRequested (void) const;

private:

  friend class DcfManager;

  uint32_t GetBackoffSlots (void) const;

  Time GetBackoffStart (void) const;

  void UpdateBackoffSlotsNow (uint32_t nSlots, Time backoffUpdateBound);

  void NotifyAccessRequested (void);

  void NotifyAccessGranted (void);

  void NotifyCollision (void);

  void NotifyInternalCollision (void);

  /**

   * Called by DcfManager to notify a DcfState subclass

   * that access to the medium is granted and can

   * start immediately.

   */

  virtual void DoNotifyAccessGranted (void) = 0;

  /**

   * Called by DcfManager to notify a DcfState subclass

   * that an 'internal' collision occured, that is, that

   * the backoff timer of a higher priority DcfState expired

   * at the same time and that access was granted to this

   * higher priority DcfState.

   *

   * The subclass is expected to start a new backoff by

   * calling DcfState::StartBackoffNow and DcfManager::RequestAccess

   * is access is still needed.

   */

  virtual void DoNotifyInternalCollision (void) = 0;

  /**

   * Called by DcfManager to notify a DcfState subclass

   * that a normal collision occured, that is, that

   * the medium was busy when access was requested.

   *

   * The subclass is expected to start a new backoff by

   * calling DcfState::StartBackoffNow and DcfManager::RequestAccess

   * is access is still needed.

   */

  virtual void DoNotifyCollision (void) = 0;

  uint32_t m_aifsn;

  uint32_t m_backoffSlots;

  // the backoffStart variable is used to keep track of the

  // time at which a backoff was started or the time at which

  // the backoff counter was last updated.

  Time m_backoffStart;

  uint32_t m_cwMin;

  uint32_t m_cwMax;

  uint32_t m_cw;

  bool m_accessRequested;

};

/**

 * \brief Manage a set of ns3::DcfState

 *

 * Handle a set of independent ns3::DcfState, each of which represents

 * a single DCF within a MAC stack. Each ns3::DcfState has a priority

 * implicitely associated with it (the priority is determined when the 

 * ns3::DcfState is added to the DcfManager: the first DcfState to be

 * added gets the highest priority, the second, the second highest

 * priority, and so on.) which is used to handle "internal" collisions.

 * i.e., when two local DcfState are expected to get access to the 

 * medium at the same time, the highest priority local DcfState wins

 * access to the medium and the other DcfState suffers a "internal" 

 * collision.

 */

class DcfManager

{

public:

  DcfManager ();

  /**

   * \param slotTime the duration of a slot.

   *

   * It is a bad idea to call this method after RequestAccess or

   * one of the Notify methods has been invoked.

   */

  /**

   * \param sifs the duration of a SIFS.

   *

   * It is a bad idea to call this method after RequestAccess or

   * one of the Notify methods has been invoked.

   */

  void SetSifs (Time sifs);

  /**

   *

   * It is a bad idea to call this method after RequestAccess or

   * one of the Notify methods has been invoked.

   */

  /**

   * \param dcf a new DcfState.

   *

   * The DcfManager does not take ownership of this pointer so, the callee

   * must make sure that the DcfState pointer will stay valid as long

   * as the DcfManager is valid. Note that the order in which DcfState

   * objects are added to a DcfManager matters: the first DcfState added

   * has the highest priority, the second DcfState added, has the second 

   * highest priority, etc.

   */

  void Add (DcfState *dcf);

  /**

   * \param state a DcfState

   *

   * Notify the DcfManager that a specific DcfState needs access to the 

   * medium. The DcfManager is then responsible for starting an access

   * timer and, invoking DcfState::DoNotifyAccessGranted when the access 

   * is granted if it ever gets granted.

   */

  void RequestAccess (DcfState *state);

  /**

   * \param duration expected duration of reception

   *

   * Notify the DCF that a packet reception started 

   * for the expected duration.

   */

  void NotifyRxStartNow (Time duration);

  /**

   * Notify the DCF that a packet reception was just

   * completed successfully.

   */

  void NotifyRxEndOkNow (void);

  /**

   * Notify the DCF that a packet reception was just

   * completed unsuccessfully.

   */

  void NotifyRxEndErrorNow (void);

  /**

   * \param duration expected duration of transmission

   *

   * Notify the DCF that a packet transmission was

   * just started and is expected to last for the specified

   * duration.

   */

  void NotifyTxStartNow (Time duration);

  /**

   * \param duration expected duration of cca busy period

   *

   * Notify the DCF that a CCA busy period has just started.

   */

  void NotifyCcaBusyStartNow (Time duration);

  /**

   * \param duration the value of the received NAV.

   *

   * Called at end of rx

   */

  void NotifyNavResetNow (Time duration);

  /**

   * \param duration the value of the received NAV.

   *

   * Called at end of rx

   */

  void NotifyNavStartNow (Time duration);

private:

  void UpdateBackoff (void);

  Time MostRecent (Time a, Time b) const;

  Time MostRecent (Time a, Time b, Time c) const;

  Time MostRecent (Time a, Time b, Time c, Time d) const;

  /**

   * Access will never be granted to the medium _before_

   * the time returned by this method.

   * 

   * \returns the absolute time at which access could start to 

   * be granted

   */

  Time GetAccessGrantStart (void) const;

  Time GetBackoffStartFor (DcfState *state);

  Time GetBackoffEndFor (DcfState *state);

  void DoRestartAccessTimeoutIfNeeded (void);

  void AccessTimeout (void);

  void DoGrantAccess (void);

  bool IsBusy (void) const;

  typedef std::vector<DcfState *> States;

  States m_states;

  Time m_lastNavStart;

  Time m_lastNavDuration;

  Time m_lastRxStart;

  Time m_lastRxDuration;

  bool m_lastRxReceivedOk;

  Time m_lastRxEnd;

  Time m_lastTxStart;

  Time m_lastTxDuration;

  Time m_lastBusyStart;

  Time m_lastBusyDuration;

  bool m_rxing;

  bool m_sleeping;

  EventId m_accessTimeout;

  Time m_slotTime;

  Time m_sifs;

};

} // namespace ns3