/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
/*
 * Copyright (c) 2014-2019,  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 "best-route-strategy2.hpp"
#include "algorithm.hpp"
#include "core/logger.hpp"

namespace nfd {
namespace fw {

NFD_LOG_INIT(BestRouteStrategy2);
NFD_REGISTER_STRATEGY(BestRouteStrategy2);

const time::milliseconds BestRouteStrategy2::RETX_SUPPRESSION_INITIAL(10);
const time::milliseconds BestRouteStrategy2::RETX_SUPPRESSION_MAX(250);

BestRouteStrategy2::BestRouteStrategy2(Forwarder& forwarder, const Name& name)
  : Strategy(forwarder)
  , ProcessNackTraits(this)
  , m_retxSuppression(RETX_SUPPRESSION_INITIAL,
                      RetxSuppressionExponential::DEFAULT_MULTIPLIER,
                      RETX_SUPPRESSION_MAX)
{
  ParsedInstanceName parsed = parseInstanceName(name);
  if (!parsed.parameters.empty()) {
    NDN_THROW(std::invalid_argument("BestRouteStrategy2 does not accept parameters"));
  }
  if (parsed.version && *parsed.version != getStrategyName()[-1].toVersion()) {
    NDN_THROW(std::invalid_argument(
      "BestRouteStrategy2 does not support version " + to_string(*parsed.version)));
  }
  this->setInstanceName(makeInstanceName(name, getStrategyName()));
}

const Name&
BestRouteStrategy2::getStrategyName()
{
  static Name strategyName("/localhost/nfd/strategy/best-route/%FD%05");
  return strategyName;
}

/** \brief determines whether a NextHop is eligible
 *  \param inFace incoming face of current Interest
 *  \param interest incoming Interest
 *  \param nexthop next hop
 *  \param pitEntry PIT entry
 *  \param wantUnused if true, NextHop must not have unexpired out-record
 *  \param now time::steady_clock::now(), ignored if !wantUnused
 */
static bool
isNextHopEligible(const Face& inFace, const Interest& interest,
                  const fib::NextHop& nexthop,
                  const shared_ptr<pit::Entry>& pitEntry,
                  bool wantUnused = false,
                  time::steady_clock::TimePoint now = time::steady_clock::TimePoint::min())
{
  const Face& outFace = nexthop.getFace();

  // do not forward back to the same face, unless it is ad hoc
  if (outFace.getId() == inFace.getId() && outFace.getLinkType() != ndn::nfd::LINK_TYPE_AD_HOC)
    return false;

  // forwarding would violate scope
  if (wouldViolateScope(inFace, interest, outFace))
    return false;

  if (wantUnused) {
    // nexthop must not have unexpired out-record
    auto outRecord = pitEntry->getOutRecord(outFace);
    if (outRecord != pitEntry->out_end() && outRecord->getExpiry() > now) {
      return false;
    }
  }

  return true;
}

/** \brief pick an eligible NextHop with earliest out-record
 *  \note It is assumed that every nexthop has an out-record.
 */
static fib::NextHopList::const_iterator
findEligibleNextHopWithEarliestOutRecord(const Face& inFace, const Interest& interest,
                                         const fib::NextHopList& nexthops,
                                         const shared_ptr<pit::Entry>& pitEntry)
{
  auto found = nexthops.end();
  auto earliestRenewed = time::steady_clock::TimePoint::max();

  for (auto it = nexthops.begin(); it != nexthops.end(); ++it) {
    if (!isNextHopEligible(inFace, interest, *it, pitEntry))
      continue;

    auto outRecord = pitEntry->getOutRecord(it->getFace());
    BOOST_ASSERT(outRecord != pitEntry->out_end());
    if (outRecord->getLastRenewed() < earliestRenewed) {
      found = it;
      earliestRenewed = outRecord->getLastRenewed();
    }
  }

  return found;
}

void
BestRouteStrategy2::afterReceiveInterest(const Face& inFace, const Interest& interest,
                                         const shared_ptr<pit::Entry>& pitEntry)
{
  RetxSuppressionResult suppression = m_retxSuppression.decidePerPitEntry(*pitEntry);
  if (suppression == RetxSuppressionResult::SUPPRESS) {
    NFD_LOG_DEBUG(interest << " from=" << inFace.getId()
                           << " suppressed");
    return;
  }

  const fib::Entry& fibEntry = this->lookupFib(*pitEntry);
  const fib::NextHopList& nexthops = fibEntry.getNextHops();
  auto it = nexthops.end();

  if (suppression == RetxSuppressionResult::NEW) {
    // forward to nexthop with lowest cost except downstream
    it = std::find_if(nexthops.begin(), nexthops.end(), [&] (const auto& nexthop) {
      return isNextHopEligible(inFace, interest, nexthop, pitEntry);
    });

    if (it == nexthops.end()) {
      NFD_LOG_DEBUG(interest << " from=" << inFace.getId() << " noNextHop");

      lp::NackHeader nackHeader;
      nackHeader.setReason(lp::NackReason::NO_ROUTE);
      this->sendNack(pitEntry, inFace, nackHeader);

      this->rejectPendingInterest(pitEntry);
      return;
    }

    Face& outFace = it->getFace();
    this->sendInterest(pitEntry, outFace, interest);
    NFD_LOG_DEBUG(interest << " from=" << inFace.getId()
                           << " newPitEntry-to=" << outFace.getId());
    return;
  }

  // find an unused upstream with lowest cost except downstream
  it = std::find_if(nexthops.begin(), nexthops.end(), [&] (const auto& nexthop) {
    return isNextHopEligible(inFace, interest, nexthop, pitEntry, true, time::steady_clock::now());
  });

  if (it != nexthops.end()) {
    Face& outFace = it->getFace();
    this->sendInterest(pitEntry, outFace, interest);
    NFD_LOG_DEBUG(interest << " from=" << inFace.getId()
                           << " retransmit-unused-to=" << outFace.getId());
    return;
  }

  // find an eligible upstream that is used earliest
  it = findEligibleNextHopWithEarliestOutRecord(inFace, interest, nexthops, pitEntry);
  if (it == nexthops.end()) {
    NFD_LOG_DEBUG(interest << " from=" << inFace.getId() << " retransmitNoNextHop");
  }
  else {
    Face& outFace = it->getFace();
    this->sendInterest(pitEntry, outFace, interest);
    NFD_LOG_DEBUG(interest << " from=" << inFace.getId()
                           << " retransmit-retry-to=" << outFace.getId());
  }
}

void
BestRouteStrategy2::afterReceiveNack(const Face& inFace, const lp::Nack& nack,
                                     const shared_ptr<pit::Entry>& pitEntry)
{
  this->processNack(inFace, nack, pitEntry);
}

} // namespace fw
} // namespace nfd