////////////////////////////////////////////////////////////////////////////////
/// DISCLAIMER
///
/// Copyright 2014-2018 ArangoDB GmbH, Cologne, Germany
/// Copyright 2004-2014 triAGENS GmbH, Cologne, Germany
///
/// Licensed under the Apache License, Version 2.0 (the "License");
/// you may not use this file except in compliance with the License.
/// You may obtain a copy of the License at
///
///     http://www.apache.org/licenses/LICENSE-2.0
///
/// Unless required by applicable law or agreed to in writing, software
/// distributed under the License is distributed on an "AS IS" BASIS,
/// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
/// See the License for the specific language governing permissions and
/// limitations under the License.
///
/// Copyright holder is ArangoDB GmbH, Cologne, Germany
///
/// @author Michael Hackstein
////////////////////////////////////////////////////////////////////////////////

#include "TraverserEngineRegistry.h"

#include "Basics/ConditionLocker.h"
#include "Basics/Exceptions.h"
#include "Basics/ReadLocker.h"
#include "Basics/WriteLocker.h"
#include "Cluster/TraverserEngine.h"
#include "Logger/Logger.h"
#include "Transaction/Context.h"
#include "VocBase/ticks.h"

#include <velocypack/Slice.h>
#include <velocypack/velocypack-aliases.h>

using namespace arangodb;
using namespace arangodb::traverser;

TraverserEngineRegistry::EngineInfo::EngineInfo(TRI_vocbase_t& vocbase,
                                                std::shared_ptr<transaction::Context> const& ctx,
                                                arangodb::velocypack::Slice info, bool needToLock)
    : _isInUse(false),
      _toBeDeleted(false),
      _engine(BaseEngine::BuildEngine(vocbase, ctx, info, needToLock)),
      _timeToLive(0),
      _expires(0) {}

TraverserEngineRegistry::EngineInfo::~EngineInfo() {}

TraverserEngineRegistry::~TraverserEngineRegistry() {
  WRITE_LOCKER(writeLocker, _lock);
  for (auto const& it : _engines) {
    destroy(it.first, false);
  }
}

/// @brief Create a new Engine and return it's id
TraverserEngineID TraverserEngineRegistry::createNew(
    TRI_vocbase_t& vocbase, std::shared_ptr<transaction::Context> const& ctx,
    arangodb::velocypack::Slice engineInfo, double ttl, /*= 600.0*/
    bool needToLock) {
  TraverserEngineID id = TRI_NewTickServer();
  LOG_TOPIC("cb2bd", DEBUG, arangodb::Logger::AQL) << "Register TraverserEngine with id " << id;
  TRI_ASSERT(id != 0);
  auto info = std::make_unique<EngineInfo>(vocbase, ctx, engineInfo, needToLock);
  info->_timeToLive = ttl;
  info->_expires = TRI_microtime() + ttl;

  WRITE_LOCKER(writeLocker, _lock);
  TRI_ASSERT(_engines.find(id) == _engines.end());
  _engines.emplace(id, info.get());
  info.release();
  return id;
}

/// @brief Destroy the engine with the given id
void TraverserEngineRegistry::destroy(TraverserEngineID id) {
  destroy(id, true);
}

/// @brief Get the engine with the given id
BaseEngine* TraverserEngineRegistry::get(TraverserEngineID id) {
  LOG_TOPIC("52d01", DEBUG, arangodb::Logger::AQL) << "Load TraverserEngine with id " << id;
  while (true) {
    {
      WRITE_LOCKER(writeLocker, _lock);
      auto e = _engines.find(id);
      if (e == _engines.end()) {
        LOG_TOPIC("c2057", DEBUG, arangodb::Logger::AQL)
            << "TraverserEngine with id " << id << " not found";
        // Nothing to hand out
        // TODO: Should we throw an error instead?
        return nullptr;
      }
      if (!e->second->_isInUse) {
        // We capture the engine
        e->second->_isInUse = true;
        LOG_TOPIC("1e69a", DEBUG, arangodb::Logger::AQL)
            << "TraverserEngine with id " << id << " is now in use";
        return e->second->_engine.get();
      }
      // Free write lock
    }

    CONDITION_LOCKER(condLocker, _cv);
    condLocker.wait(1000);
  }
  // Unreachable the above loop can only be left by error or return;
  TRI_ASSERT(false);
  return nullptr;
}

/// @brief Returns the engine to the registry. Someone else can now use it.
void TraverserEngineRegistry::returnEngine(TraverserEngineID id, double ttl) {
  LOG_TOPIC("e6ad2", DEBUG, arangodb::Logger::AQL)
      << "Returning TraverserEngine with id " << id;
  WRITE_LOCKER(writeLocker, _lock);
  auto e = _engines.find(id);
  if (e == _engines.end()) {
    // Nothing to return
    LOG_TOPIC("6ab92", DEBUG, arangodb::Logger::AQL) << "TraverserEngine with id " << id << " not found";
    return;
  }
  if (e->second->_isInUse) {
    e->second->_isInUse = false;
    if (e->second->_toBeDeleted) {
      auto engine = e->second;
      _engines.erase(e);
      delete engine;
      LOG_TOPIC("2e367", DEBUG, arangodb::Logger::AQL)
          << "TraverserEngine with id " << id << " is now deleted";
    } else {
      if (ttl >= 0.0) {
        e->second->_timeToLive = ttl;
      }
      e->second->_expires = TRI_microtime() + e->second->_timeToLive;

      LOG_TOPIC("40973", DEBUG, arangodb::Logger::AQL)
          << "TraverserEngine with id " << id << " is now free";
    }
    // Lockgard send signal auf conditionvar
    CONDITION_LOCKER(condLocker, _cv);
    condLocker.broadcast();
  }
}

/// @brief Destroy the engine with the given id, worker function
void TraverserEngineRegistry::destroy(TraverserEngineID id, bool doLock) {
  LOG_TOPIC("e7e96", DEBUG, arangodb::Logger::AQL)
      << "Destroying TraverserEngine with id " << id;
  EngineInfo* engine = nullptr;

  {
    CONDITIONAL_WRITE_LOCKER(writeLocker, _lock, doLock);
    auto e = _engines.find(id);
    if (e == _engines.end()) {
      // Nothing to destroy
      return;
    }
    // TODO what about shard locking?
    // TODO what about multiple dbs?
    if (e->second->_isInUse) {
      LOG_TOPIC("6906e", DEBUG, arangodb::Logger::AQL)
          << "TraverserEngine with id " << id << " still in use, sending kill";
      // Someone is still working with this engine. Mark it as to be deleted
      e->second->_toBeDeleted = true;
      return;
    }

    engine = e->second;
    _engines.erase(id);
  }
  LOG_TOPIC("fd318", DEBUG, arangodb::Logger::AQL)
      << "TraverserEngine with id " << id << " is now destroyed";

  delete engine;
}

/// @brief expireEngines
void TraverserEngineRegistry::expireEngines() {
  double now = TRI_microtime();
  std::vector<TraverserEngineID> toDelete;

  {
    WRITE_LOCKER(writeLocker, _lock);
    for (auto& y : _engines) {
      // y.first is an TraverserEngineID and
      // y.second is an EngineInfo*
      EngineInfo*& ei = y.second;
      if (!ei->_isInUse && now > ei->_expires) {
        toDelete.emplace_back(y.first);
      }
    }
  }

  for (auto& p : toDelete) {
    try {  // just in case
      LOG_TOPIC("f0ec7", DEBUG, arangodb::Logger::AQL)
          << "Destroy TraverserEngine with id " << p << " because of timeout";
      destroy(p, true);
    } catch (...) {
    }
  }
}

/// @brief return number of registered engines
size_t TraverserEngineRegistry::numberRegisteredEngines() {
  READ_LOCKER(readLocker, _lock);
  return _engines.size();
}

/// @brief destroy all registered engines
void TraverserEngineRegistry::destroyAll() {
  std::vector<TraverserEngineID> engines;
  {
    READ_LOCKER(readLocker, _lock);
    for (auto& p : _engines) {
      engines.push_back(p.first);
    }
  }
  for (auto& i : engines) {
    LOG_TOPIC("e6e47", DEBUG, arangodb::Logger::AQL)
        << "Destroy TraverserEngine with id " << i << " due to shutdown";
    destroy(i, true);
  }
}