/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
/**
 * Copyright (c) 2014-2016,  Regents of the University of California,
 *                           Arizona Board of Regents,
 *                           Colorado State University,
 *                           University Pierre & Marie Curie, Sorbonne University,
 *                           Washington University in St. Louis,
 *                           Beijing Institute of Technology,
 *                           The University of Memphis.
 *
 * This file is part of NFD (Named Data Networking Forwarding Daemon).
 * See AUTHORS.md for complete list of NFD authors and contributors.
 *
 * NFD is free software: you can redistribute it and/or modify it under the terms
 * of the GNU General Public License as published by the Free Software Foundation,
 * either version 3 of the License, or (at your option) any later version.
 *
 * NFD 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
 * NFD, e.g., in COPYING.md file.  If not, see <http://www.gnu.org/licenses/>.
 */

#include "ncc-strategy.hpp"
#include "pit-algorithm.hpp"
#include "core/random.hpp"

namespace nfd {
namespace fw {

const Name NccStrategy::STRATEGY_NAME("ndn:/localhost/nfd/strategy/ncc/%FD%01");
NFD_REGISTER_STRATEGY(NccStrategy);

NccStrategy::NccStrategy(Forwarder& forwarder, const Name& name)
  : Strategy(forwarder, name)
{
}

const time::microseconds NccStrategy::DEFER_FIRST_WITHOUT_BEST_FACE = time::microseconds(4000);
const time::microseconds NccStrategy::DEFER_RANGE_WITHOUT_BEST_FACE = time::microseconds(75000);
const time::nanoseconds NccStrategy::MEASUREMENTS_LIFETIME = time::seconds(16);

void
NccStrategy::afterReceiveInterest(const Face& inFace, const Interest& interest,
                                  const shared_ptr<pit::Entry>& pitEntry)
{
  const fib::Entry& fibEntry = this->lookupFib(*pitEntry);
  const fib::NextHopList& nexthops = fibEntry.getNextHops();
  if (nexthops.size() == 0) {
    this->rejectPendingInterest(pitEntry);
    return;
  }

  PitEntryInfo* pitEntryInfo = pitEntry->insertStrategyInfo<PitEntryInfo>().first;
  bool isNewPitEntry = !hasPendingOutRecords(*pitEntry);
  if (!isNewPitEntry) {
    return;
  }

  MeasurementsEntryInfo& meInfo = this->getMeasurementsEntryInfo(pitEntry);

  time::microseconds deferFirst = DEFER_FIRST_WITHOUT_BEST_FACE;
  time::microseconds deferRange = DEFER_RANGE_WITHOUT_BEST_FACE;
  size_t nUpstreams = nexthops.size();

  shared_ptr<Face> bestFace = meInfo.getBestFace();
  if (bestFace != nullptr && fibEntry.hasNextHop(*bestFace) &&
      canForwardToLegacy(*pitEntry, *bestFace)) {
    // TODO Should we use `randlow = 100 + nrand48(h->seed) % 4096U;` ?
    deferFirst = meInfo.prediction;
    deferRange = time::microseconds((deferFirst.count() + 1) / 2);
    --nUpstreams;
    this->sendInterest(pitEntry, *bestFace);
    pitEntryInfo->bestFaceTimeout = scheduler::schedule(
      meInfo.prediction,
      bind(&NccStrategy::timeoutOnBestFace, this, weak_ptr<pit::Entry>(pitEntry)));
  }
  else {
    // use first eligible nexthop
    auto firstEligibleNexthop = std::find_if(nexthops.begin(), nexthops.end(),
        [&pitEntry] (const fib::NextHop& nexthop) {
          return canForwardToLegacy(*pitEntry, nexthop.getFace());
        });
    if (firstEligibleNexthop != nexthops.end()) {
      this->sendInterest(pitEntry, firstEligibleNexthop->getFace());
    }
  }

  shared_ptr<Face> previousFace = meInfo.previousFace.lock();
  if (previousFace != nullptr && fibEntry.hasNextHop(*previousFace) &&
      canForwardToLegacy(*pitEntry, *previousFace)) {
    --nUpstreams;
  }

  if (nUpstreams > 0) {
    pitEntryInfo->maxInterval = std::max(time::microseconds(1),
      time::microseconds((2 * deferRange.count() + nUpstreams - 1) / nUpstreams));
  }
  else {
    // Normally, maxInterval is unused if there aren't any face beyond best and previousBest.
    // However, in case FIB entry gains a new nexthop before doPropagate executes (bug 1853),
    // this maxInterval would be used to determine when the next doPropagate would happen.
    pitEntryInfo->maxInterval = deferFirst;
  }
  pitEntryInfo->propagateTimer = scheduler::schedule(deferFirst,
    bind(&NccStrategy::doPropagate, this, weak_ptr<pit::Entry>(pitEntry)));
}

void
NccStrategy::doPropagate(weak_ptr<pit::Entry> pitEntryWeak)
{
  shared_ptr<pit::Entry> pitEntry = pitEntryWeak.lock();
  if (pitEntry == nullptr) {
    return;
  }
  const fib::Entry& fibEntry = this->lookupFib(*pitEntry);

  PitEntryInfo* pitEntryInfo = pitEntry->getStrategyInfo<PitEntryInfo>();
  // pitEntryInfo is guaranteed to exist here, because doPropagate is triggered
  // from a timer set by NccStrategy.
  BOOST_ASSERT(pitEntryInfo != nullptr);

  MeasurementsEntryInfo& meInfo = this->getMeasurementsEntryInfo(pitEntry);

  shared_ptr<Face> previousFace = meInfo.previousFace.lock();
  if (previousFace != nullptr && fibEntry.hasNextHop(*previousFace) &&
      canForwardToLegacy(*pitEntry, *previousFace)) {
    this->sendInterest(pitEntry, *previousFace);
  }

  const fib::NextHopList& nexthops = fibEntry.getNextHops();
  bool isForwarded = false;
  for (fib::NextHopList::const_iterator it = nexthops.begin(); it != nexthops.end(); ++it) {
    Face& face = it->getFace();
    if (canForwardToLegacy(*pitEntry, face)) {
      isForwarded = true;
      this->sendInterest(pitEntry, face);
      break;
    }
  }

  if (isForwarded) {
    std::uniform_int_distribution<time::nanoseconds::rep> dist(0, pitEntryInfo->maxInterval.count() - 1);
    time::nanoseconds deferNext = time::nanoseconds(dist(getGlobalRng()));
    pitEntryInfo->propagateTimer = scheduler::schedule(deferNext,
      bind(&NccStrategy::doPropagate, this, weak_ptr<pit::Entry>(pitEntry)));
  }
}

void
NccStrategy::timeoutOnBestFace(weak_ptr<pit::Entry> pitEntryWeak)
{
  shared_ptr<pit::Entry> pitEntry = pitEntryWeak.lock();
  if (pitEntry == nullptr) {
    return;
  }
  measurements::Entry* measurementsEntry = this->getMeasurements().get(*pitEntry);

  for (int i = 0; i < UPDATE_MEASUREMENTS_N_LEVELS; ++i) {
    if (measurementsEntry == nullptr) {
      // going out of this strategy's namespace
      break;
    }
    this->getMeasurements().extendLifetime(*measurementsEntry, MEASUREMENTS_LIFETIME);

    MeasurementsEntryInfo& meInfo = this->getMeasurementsEntryInfo(measurementsEntry);
    meInfo.adjustPredictUp();

    measurementsEntry = this->getMeasurements().getParent(*measurementsEntry);
  }
}

void
NccStrategy::beforeSatisfyInterest(const shared_ptr<pit::Entry>& pitEntry,
                                   const Face& inFace, const Data& data)
{
  if (!pitEntry->hasInRecords()) {
    // PIT entry has already been satisfied (and is now waiting for straggler timer to expire)
    // NCC does not collect measurements for non-best face
    return;
  }

  measurements::Entry* measurementsEntry = this->getMeasurements().get(*pitEntry);

  for (int i = 0; i < UPDATE_MEASUREMENTS_N_LEVELS; ++i) {
    if (measurementsEntry == nullptr) {
      // going out of this strategy's namespace
      return;
    }
    this->getMeasurements().extendLifetime(*measurementsEntry, MEASUREMENTS_LIFETIME);

    MeasurementsEntryInfo& meInfo = this->getMeasurementsEntryInfo(measurementsEntry);
    meInfo.updateBestFace(inFace);

    measurementsEntry = this->getMeasurements().getParent(*measurementsEntry);
  }

  PitEntryInfo* pitEntryInfo = pitEntry->getStrategyInfo<PitEntryInfo>();
  if (pitEntryInfo != nullptr) {
    scheduler::cancel(pitEntryInfo->propagateTimer);

    // Verify that the best face satisfied the interest before canceling the timeout call
    MeasurementsEntryInfo& meInfo = this->getMeasurementsEntryInfo(pitEntry);
    shared_ptr<Face> bestFace = meInfo.getBestFace();

    if (bestFace.get() == &inFace)
      scheduler::cancel(pitEntryInfo->bestFaceTimeout);
  }
}

NccStrategy::MeasurementsEntryInfo&
NccStrategy::getMeasurementsEntryInfo(const shared_ptr<pit::Entry>& entry)
{
  measurements::Entry* measurementsEntry = this->getMeasurements().get(*entry);
  return this->getMeasurementsEntryInfo(measurementsEntry);
}

NccStrategy::MeasurementsEntryInfo&
NccStrategy::getMeasurementsEntryInfo(measurements::Entry* entry)
{
  BOOST_ASSERT(entry != nullptr);
  MeasurementsEntryInfo* info = nullptr;
  bool isNew = false;
  std::tie(info, isNew) = entry->insertStrategyInfo<MeasurementsEntryInfo>();
  if (!isNew) {
    return *info;
  }

  measurements::Entry* parentEntry = this->getMeasurements().getParent(*entry);
  if (parentEntry != nullptr) {
    MeasurementsEntryInfo& parentInfo = this->getMeasurementsEntryInfo(parentEntry);
    info->inheritFrom(parentInfo);
  }

  return *info;
}

const time::microseconds NccStrategy::MeasurementsEntryInfo::INITIAL_PREDICTION = time::microseconds(8192);
const time::microseconds NccStrategy::MeasurementsEntryInfo::MIN_PREDICTION = time::microseconds(127);
const time::microseconds NccStrategy::MeasurementsEntryInfo::MAX_PREDICTION = time::milliseconds(160);

NccStrategy::MeasurementsEntryInfo::MeasurementsEntryInfo()
  : prediction(INITIAL_PREDICTION)
{
}

void
NccStrategy::MeasurementsEntryInfo::inheritFrom(const MeasurementsEntryInfo& other)
{
  this->operator=(other);
}

shared_ptr<Face>
NccStrategy::MeasurementsEntryInfo::getBestFace()
{
  shared_ptr<Face> best = this->bestFace.lock();
  if (best != nullptr) {
    return best;
  }
  this->bestFace = best = this->previousFace.lock();
  return best;
}

void
NccStrategy::MeasurementsEntryInfo::updateBestFace(const Face& face)
{
  if (this->bestFace.expired()) {
    this->bestFace = const_cast<Face&>(face).shared_from_this();
    return;
  }
  shared_ptr<Face> bestFace = this->bestFace.lock();
  if (bestFace.get() == &face) {
    this->adjustPredictDown();
  }
  else {
    this->previousFace = this->bestFace;
    this->bestFace = const_cast<Face&>(face).shared_from_this();
  }
}

void
NccStrategy::MeasurementsEntryInfo::adjustPredictDown()
{
  prediction = std::max(MIN_PREDICTION,
    time::microseconds(prediction.count() - (prediction.count() >> ADJUST_PREDICT_DOWN_SHIFT)));
}

void
NccStrategy::MeasurementsEntryInfo::adjustPredictUp()
{
  prediction = std::min(MAX_PREDICTION,
    time::microseconds(prediction.count() + (prediction.count() >> ADJUST_PREDICT_UP_SHIFT)));
}

void
NccStrategy::MeasurementsEntryInfo::ageBestFace()
{
  this->previousFace = this->bestFace;
  this->bestFace.reset();
}

NccStrategy::PitEntryInfo::~PitEntryInfo()
{
  scheduler::cancel(this->bestFaceTimeout);
  scheduler::cancel(this->propagateTimer);
}

} // namespace fw
} // namespace nfd