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

#include "ns3/assert.h"

#include "ns3/log.h"

#include "ns3/simulator.h"

#include <math.h>

#include "dcf-manager.h"

#include "wifi-phy.h"

#include "wifi-mac.h"

#include "mac-low.h"

NS_LOG_COMPONENT_DEFINE ("DcfManager");

#define MY_DEBUG(x) \

  NS_LOG_DEBUG (Simulator::Now () << " " << this << " " << x)

namespace ns3 {

/****************************************************************

 *      Implement the DCF state holder

 ****************************************************************/

DcfState::DcfState ()

  : m_backoffSlots (0),

    m_backoffStart (Seconds (0.0)),

    m_cwMin (0),

    m_cwMax (0),

    m_cw (0),

    m_accessRequested (false)

{}

DcfState::~DcfState ()

{}

void 

DcfState::SetAifsn (uint32_t aifsn)

{

  m_aifsn = aifsn;

}

void 

DcfState::SetCwMin (uint32_t minCw)

{

  m_cwMin = minCw;

  ResetCw ();

}

void 

DcfState::SetCwMax (uint32_t maxCw)

{

  m_cwMax = maxCw;

  ResetCw ();

}

uint32_t 

DcfState::GetAifsn (void) const

{

  return m_aifsn;

}

uint32_t

DcfState::GetCwMin (void) const

{

  return m_cwMin;

}

uint32_t 

DcfState::GetCwMax (void) const

{

  return m_cwMax;

}

void 

DcfState::ResetCw (void)

{

  m_cw = m_cwMin;

}

void 

DcfState::UpdateFailedCw (void)

{

  uint32_t cw = m_cw;

  cw *= 2;

  cw = std::min (m_cwMax, cw);

  m_cw = cw;

}

void 

DcfState::UpdateBackoffSlotsNow (uint32_t nSlots, Time backoffUpdateBound)

{

  m_backoffSlots -= nSlots;

  m_backoffStart = backoffUpdateBound;

  MY_DEBUG ("update slots="<<nSlots<<" slots, backoff="<<m_backoffSlots);

}

void 

DcfState::StartBackoffNow (uint32_t nSlots)

{

  NS_ASSERT (m_backoffSlots == 0);

  MY_DEBUG ("start backoff="<<nSlots<<" slots");

  m_backoffSlots = nSlots;

  m_backoffStart = Simulator::Now ();

}

uint32_t

DcfState::GetCw (void) const

{

  return m_cw;

}

uint32_t 

DcfState::GetBackoffSlots (void) const

{

  return m_backoffSlots;

}

Time 

DcfState::GetBackoffStart (void) const

{

  return m_backoffStart;

}

bool 

DcfState::IsAccessRequested (void) const

{

  return m_accessRequested;

}

void 

DcfState::NotifyAccessRequested (void)

{

  m_accessRequested = true;

}

void 

DcfState::NotifyAccessGranted (void)

{

  NS_ASSERT (m_accessRequested);

  m_accessRequested = false;

  DoNotifyAccessGranted ();

}

void 

DcfState::NotifyCollision (void)

{

  DoNotifyCollision ();

}

void 

DcfState::NotifyInternalCollision (void)

{

  DoNotifyInternalCollision ();

}

/***************************************************************

 *         Listener for Nav events. Forwards to DcfManager

 ***************************************************************/

class LowNavListener : public ns3::MacLowNavListener {

public:

  LowNavListener (ns3::DcfManager *dcf)

    : m_dcf (dcf) {}

  virtual ~LowNavListener () {}

  virtual void NavStart (Time duration) {

    m_dcf->NotifyNavStartNow (duration);

  }

  virtual void NavReset (Time duration) {

    m_dcf->NotifyNavResetNow (duration);

  }

private:

  ns3::DcfManager *m_dcf;

};

/***************************************************************

 *         Listener for PHY events. Forwards to DcfManager

 ***************************************************************/

class PhyListener : public ns3::WifiPhyListener {

public:

  PhyListener (ns3::DcfManager *dcf)

    : m_dcf (dcf) {}

  virtual ~PhyListener () {}

  virtual void NotifyRxStart (Time duration) {

    m_dcf->NotifyRxStartNow (duration);

  }

  virtual void NotifyRxEndOk (void) {

    m_dcf->NotifyRxEndOkNow ();

  }

  virtual void NotifyRxEndError (void) {

    m_dcf->NotifyRxEndErrorNow ();

  }

  virtual void NotifyTxStart (Time duration) {

    m_dcf->NotifyTxStartNow (duration);

  }

  }

private:

  ns3::DcfManager *m_dcf;

};

/****************************************************************

 *      Implement the DCF manager of all DCF state holders

 ****************************************************************/

DcfManager::DcfManager ()

  : m_lastNavStart (MicroSeconds (0)),

    m_lastNavDuration (MicroSeconds (0)),

    m_lastRxStart (MicroSeconds (0)),

    m_lastRxDuration (MicroSeconds (0)),

    m_lastRxReceivedOk (true),

    m_lastRxEnd (MicroSeconds (0)),

    m_lastTxStart (MicroSeconds (0)),

    m_lastTxDuration (MicroSeconds (0)),

    m_lastBusyStart (MicroSeconds (0)),

    m_lastBusyDuration (MicroSeconds (0)),

    m_rxing (false),

    m_slotTime (Seconds (0.0)),

    m_sifs (Seconds (0.0)),

    m_phyListener (0),

    m_lowListener (0)

{}

DcfManager::~DcfManager ()

{

  delete m_phyListener;

  delete m_lowListener;

  m_phyListener = 0;

  m_lowListener = 0;

}

void 

DcfManager::SetupPhyListener (Ptr<WifiPhy> phy)

{

  m_phyListener = new PhyListener (this);

  phy->RegisterListener (m_phyListener);

}

void 

DcfManager::SetupLowListener (Ptr<MacLow> low)

{

  m_lowListener = new LowNavListener (this);

  low->RegisterNavListener (m_lowListener);

}

void 

DcfManager::SetSlot (Time slotTime)

{

  m_slotTime = slotTime;

}

void 

DcfManager::SetSifs (Time sifs)

{

  m_sifs = sifs;

}

void 

DcfManager::SetEifsNoDifs (Time eifsNoDifs)

{

  m_eifsNoDifs = eifsNoDifs;

}

void 

DcfManager::Add (DcfState *dcf)

{

  m_states.push_back (dcf);

}

Time

DcfManager::MostRecent (Time a, Time b) const

{

  return Max (a, b);

}

Time

DcfManager::MostRecent (Time a, Time b, Time c) const

{

  Time retval;

  retval = Max (a, b);

  retval = Max (retval, c);

  return retval;

}

Time

DcfManager::MostRecent (Time a, Time b, Time c, Time d) const

{

  Time e = Max (a, b);

  Time f = Max (c, d);

  Time retval = Max (e, f);

  return retval;

}

bool 

DcfManager::IsBusy (void) const

{

  // PHY busy

  if (m_rxing) 

    {

      return true;

    }

  Time lastTxEnd = m_lastTxStart + m_lastTxDuration;

  if (lastTxEnd > Simulator::Now ()) 

    {

      return true;

    }

  // NAV busy

  Time lastNavEnd = m_lastNavStart + m_lastNavDuration;

  if (lastNavEnd > Simulator::Now ())

    {

      return true;

    }

  return false;

}

void 

DcfManager::RequestAccess (DcfState *state)

{

  UpdateBackoff ();

  NS_ASSERT (!state->IsAccessRequested ());

  state->NotifyAccessRequested ();

  /**

   * If there is a collision, generate a backoff

   * by notifying the collision to the user.

   */

  if (state->GetBackoffSlots () == 0 && 

      IsBusy ())

    {

      MY_DEBUG ("medium is busy: collision");

      /* someone else has accessed the medium.

       * generate a backoff.

       */

      state->NotifyCollision ();

    }

  DoGrantAccess ();

  DoRestartAccessTimeoutIfNeeded ();  

}

void

DcfManager::DoGrantAccess (void)

{

  Time accessGrantStart = GetAccessGrantStart ();

  uint32_t k = 0;

  for (States::const_iterator i = m_states.begin (); i != m_states.end (); k++)

    {

      DcfState *state = *i;

      if (state->IsAccessRequested () && 

          GetBackoffEndFor (state) <= Simulator::Now ())

        {

          /**

           * This is the first dcf we find with an expired backoff and which

           * needs access to the medium. i.e., it has data to send.

           */

          MY_DEBUG ("dcf " << k << " needs access. backoff expired. access granted. slots="<<state->GetBackoffSlots ());

          i++; // go to the next item in the list.

          k++;

          std::vector<DcfState *> internalCollisionStates;

          for (States::const_iterator j = i; j != m_states.end (); j++, k++)

            {

              DcfState *otherState = *j;

              if (otherState->IsAccessRequested () &&

                  GetBackoffEndFor (otherState) <= Simulator::Now ())

                {

                  MY_DEBUG ("dcf " << k << " needs access. backoff expired. internal collision. slots=" << 

                            otherState->GetBackoffSlots ());

                  /**

                   * all other dcfs with a lower priority whose backoff

                   * has expired and which needed access to the medium

                   * must be notified that we did get an internal collision.

                   */

                  internalCollisionStates.push_back (otherState);

                }

            }

          /**

           * Now, we notify all of these changes in one go. It is necessary to 

           * perform first the calculations of which states are colliding and then

           * only apply the changes because applying the changes through notification

           * could change the global state of the manager, and, thus, could change

           * the result of the calculations. 

           */

          state->NotifyAccessGranted ();

          for (std::vector<DcfState *>::const_iterator k = internalCollisionStates.begin ();

               k != internalCollisionStates.end (); k++)

            {

              (*k)->NotifyInternalCollision ();

            }

          break;

        }

      i++;

    }

}

void

DcfManager::AccessTimeout (void)

{

  UpdateBackoff ();

  DoGrantAccess ();

  DoRestartAccessTimeoutIfNeeded ();

}

Time

DcfManager::GetAccessGrantStart (void) const

{

  Time rxAccessStart;

  if (m_lastRxEnd >= m_lastRxStart) 

    {

      rxAccessStart = m_lastRxEnd;

      if (!m_lastRxReceivedOk)

        {

          rxAccessStart += m_eifsNoDifs;

        }

      else

        {

          rxAccessStart += m_sifs;

        }

    } 

  else 

    {

      rxAccessStart = m_lastRxStart + m_lastRxDuration + m_sifs;

    }

  Time busyAccessStart = m_lastBusyStart + m_lastBusyDuration + m_sifs;

  Time txAccessStart = m_lastTxStart + m_lastTxDuration + m_sifs;

  Time navAccessStart = m_lastNavStart + m_lastNavDuration + m_sifs;

  Time accessGrantedStart = MostRecent (rxAccessStart, 

                                        busyAccessStart,

                                        txAccessStart, 

                                        navAccessStart);

  NS_LOG_INFO ("access grant start=" << accessGrantedStart <<

               ", rx access start=" << rxAccessStart <<

               ", busy access start=" << busyAccessStart <<

               ", tx access start=" << txAccessStart <<

               ", nav access start=" << navAccessStart);

  return accessGrantedStart;

}

Time

DcfManager::GetBackoffStartFor (DcfState *state)

{

  Time mostRecentEvent = MostRecent (state->GetBackoffStart (),

                                     GetAccessGrantStart () + Scalar (state->GetAifsn ()) * m_slotTime);

  return mostRecentEvent;

}

Time

DcfManager::GetBackoffEndFor (DcfState *state)

{

  return GetBackoffStartFor (state) + Scalar (state->GetBackoffSlots ()) * m_slotTime;

}

void

DcfManager::UpdateBackoff (void)

{

  uint32_t k = 0;

  for (States::const_iterator i = m_states.begin (); i != m_states.end (); i++, k++)

    {

      DcfState *state = *i;

      Time backoffStart = GetBackoffStartFor (state);

      if (backoffStart <= Simulator::Now ())

        {

          Scalar nSlots = (Simulator::Now () - backoffStart) / m_slotTime;

          uint32_t nIntSlots = lrint (nSlots.GetDouble ());          

          uint32_t n = std::min (nIntSlots, state->GetBackoffSlots ());

          MY_DEBUG ("dcf " << k << " dec backoff slots=" << n);

          Time backoffUpdateBound = backoffStart + Scalar (n) * m_slotTime;

          state->UpdateBackoffSlotsNow (n, backoffUpdateBound);

        }

    }

}

void

DcfManager::DoRestartAccessTimeoutIfNeeded (void)

{

  /**

   * Is there a DcfState which needs to access the medium, and, 

   * if there is one, how many slots for AIFS+backoff does it require ?

   */

  bool accessTimeoutNeeded = false;

  Time expectedBackoffEnd = Simulator::GetMaximumSimulationTime ();

  for (States::const_iterator i = m_states.begin (); i != m_states.end (); i++)

    {

      DcfState *state = *i;

      if (state->IsAccessRequested ())

        {

          Time tmp = GetBackoffEndFor (state);

          if (tmp > Simulator::Now ())

            {

              accessTimeoutNeeded = true;

              expectedBackoffEnd = std::min (expectedBackoffEnd, tmp);

            }

        }

    }

  if (accessTimeoutNeeded)

    {

      MY_DEBUG ("expected backoff end="<<expectedBackoffEnd);

      Time expectedBackoffDelay = expectedBackoffEnd - Simulator::Now ();

      if (m_accessTimeout.IsRunning () &&

          Simulator::GetDelayLeft (m_accessTimeout) > expectedBackoffDelay)

        {

          m_accessTimeout.Cancel ();

        }

      if (m_accessTimeout.IsExpired ())

        {

          m_accessTimeout = Simulator::Schedule (expectedBackoffDelay,

                                                 &DcfManager::AccessTimeout, this);

        }

    }

}

void 

DcfManager::NotifyRxStartNow (Time duration)

{

  MY_DEBUG ("rx start for="<<duration);

  UpdateBackoff ();

  m_lastRxStart = Simulator::Now ();