/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
//
// Copyright (c) 2006 Georgia Tech Research Corporation
//           (c) 2013 University of Arizona
//           (c) 2013 University of California, Los Angeles
//
// 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: Rajib Bhattacharjea<raj.b@gatech.edu>
//         Cheng Yi <yic@email.arizona.edu>
//         Alexander Afanasyev <alexander.afanasyev@ucla.edu>
//

// Georgia Tech Network Simulator - Round Trip Time Estimation Class
// George F. Riley.  Georgia Tech, Spring 2002

#include "ndn-rtt-mean-deviation.h"
#include "ns3/simulator.h"
#include "ns3/double.h"
#include "ns3/integer.h"
#include "ns3/uinteger.h"
#include "ns3/log.h"

NS_LOG_COMPONENT_DEFINE ("ndn.RttMeanDeviation");

namespace ns3 {
namespace ndn {

//---------------------------------------------------------------------------------
// A modified version of Mean-Deviation Estimator optimized for NDN packet delivery

NS_OBJECT_ENSURE_REGISTERED (RttMeanDeviation);

TypeId
RttMeanDeviation::GetTypeId (void)
{
  static TypeId tid = TypeId ("ns3::ndn::RttMeanDeviation")
    .SetParent<RttEstimator> ()
    .AddConstructor<RttMeanDeviation> ()
    .AddAttribute ("Gain",
                   "Gain used in estimating the RTT (smoothed RTT), must be 0 < Gain < 1",
                   DoubleValue (0.125),
                   MakeDoubleAccessor (&RttMeanDeviation::m_gain),
                   MakeDoubleChecker<double> ())
    .AddAttribute ("Gain2",
                   "Gain2 used in estimating the RTT (variance), must be 0 < Gain2 < 1",
                   DoubleValue (0.25),
                   MakeDoubleAccessor (&RttMeanDeviation::m_gain2),
                   MakeDoubleChecker<double> ())
  ;
  return tid;
}

RttMeanDeviation::RttMeanDeviation() :
  m_variance (0)
{
  NS_LOG_FUNCTION (this);
}

RttMeanDeviation::RttMeanDeviation (const RttMeanDeviation& c)
  : RttEstimator (c), m_gain (c.m_gain), m_gain2 (c.m_gain2), m_variance (c.m_variance)
{
  NS_LOG_FUNCTION (this);
}

void RttMeanDeviation::Measurement (Time m)
{
  NS_LOG_FUNCTION (this << m);
  if (m_nSamples)
    { // Not first
      Time err (m - m_currentEstimatedRtt);
      double gErr = err.ToDouble (Time::S) * m_gain;
      m_currentEstimatedRtt += Time::FromDouble (gErr, Time::S);
      Time difference = Abs (err) - m_variance;
      NS_LOG_DEBUG ("m_variance += " << Time::FromDouble (difference.ToDouble (Time::S) * m_gain2, Time::S));
      m_variance += Time::FromDouble (difference.ToDouble (Time::S) * m_gain2, Time::S);
    }
  else
    { // First sample
      m_currentEstimatedRtt = m;             // Set estimate to current
      //variance = sample / 2;               // And variance to current / 2
      // m_variance = m; // try this  why????
      m_variance = Seconds (m.ToDouble (Time::S) / 2);
      NS_LOG_DEBUG ("(first sample) m_variance += " << m);
    }
  m_nSamples++;
}

Time RttMeanDeviation::RetransmitTimeout ()
{
  NS_LOG_FUNCTION (this);

  double retval = std::min (m_maxRto.ToDouble (Time::S),
                            std::max (m_multiplier*m_minRto.ToDouble (Time::S),
                                      m_multiplier*(m_currentEstimatedRtt.ToDouble (Time::S) + 4 * m_variance.ToDouble (Time::S))));

  NS_LOG_DEBUG ("RetransmitTimeout:  return " << retval);

  return Seconds (retval);
}

Ptr<RttEstimator> RttMeanDeviation::Copy () const
{
  NS_LOG_FUNCTION (this);
  return CopyObject<RttMeanDeviation> (this);
}

void RttMeanDeviation::Reset ()
{
  NS_LOG_FUNCTION (this);
  // Reset to initial state
  m_variance = Seconds (0);
  RttEstimator::Reset ();
}

void RttMeanDeviation::Gain (double g)
{
  NS_LOG_FUNCTION (this);
  NS_ASSERT_MSG( (g > 0) && (g < 1), "RttMeanDeviation: Gain must be less than 1 and greater than 0" );
  m_gain = g;
}

Time RttMeanDeviation::AckSeq (SequenceNumber32 ackSeq)
{
  NS_LOG_FUNCTION (this << ackSeq);
  // An ack has been received, calculate rtt and log this measurement
  // Note we use a linear search (O(n)) for this since for the common
  // case the ack'ed packet will be at the head of the list
  Time m = Seconds (0.0);
  if (m_history.size () == 0) return (m);    // No pending history, just exit

  for (RttHistory_t::iterator i = m_history.begin (); i != m_history.end (); ++i)
  {
      if (ackSeq == i->seq)
      { // Found it
          m = Simulator::Now () - i->time;// Elapsed time
          Measurement (m);                // Log the measurement
          ResetMultiplier ();             // Reset multiplier on valid measurement
          m_history.erase(i);
          break;
      }
  }

  return m;
}

} // namespace ndn
} // namespace ns3