////////////////////////////////////////////////////////////////////////////////
/// DISCLAIMER
///
/// Copyright 2014-2016 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 Dr. Frank Celler
/// @author Achim Brandt
////////////////////////////////////////////////////////////////////////////////

#ifndef ARANGOD_SCHEDULER_SCHEDULER_H
#define ARANGOD_SCHEDULER_SCHEDULER_H 1

#include "Basics/Common.h"

#include <boost/asio/steady_timer.hpp>

#include "Basics/Mutex.h"
#include "Basics/asio-helper.h"
#include "Basics/socket-utils.h"
#include "Scheduler/EventLoop.h"
#include "Scheduler/Job.h"

namespace arangodb {
class JobQueue;
class JobGuard;

namespace basics {
class ConditionVariable;
}
namespace velocypack {
class Builder;
}

namespace rest {

class Scheduler {
  Scheduler(Scheduler const&) = delete;
  Scheduler& operator=(Scheduler const&) = delete;

  friend class arangodb::JobGuard;

 public:
  Scheduler(uint64_t nrMinimum, uint64_t nrDesired, uint64_t nrMaximum,
            uint64_t maxQueueSize);
  virtual ~Scheduler();

 public:
  boost::asio::io_service* ioService() const { return _ioService.get(); }
  boost::asio::io_service* managerService() const {
    return _managerService.get();
  }

  EventLoop eventLoop() {
    // return EventLoop{._ioService = *_ioService.get(), ._scheduler = this};
    // windows complains ...
    return EventLoop{_ioService.get(), this};
  }

  void post(std::function<void()> callback);

  bool start(basics::ConditionVariable*);
  bool isRunning() const { return numRunning(_counters) > 0; }

  void beginShutdown();
  void stopRebalancer() noexcept;
  bool isStopping() { return (_counters & (1ULL << 63)) != 0; }
  void shutdown();

 public:
  // decrements the nrRunning counter for the thread
  void stopThread();

  // check if the current thread should be stopped
  // returns true if yes, otherwise false. when the function returns
  // true, it has already decremented the nrRunning counter!
  bool stopThreadIfTooMany(double now);

  bool shouldQueueMore() const;
  bool hasQueueCapacity() const;

  bool queue(std::unique_ptr<Job> job);

  uint64_t minimum() const { return _nrMinimum; }

  std::string infoStatus();

  inline void queueJob() noexcept { ++_nrQueued; } 
  inline void unqueueJob() noexcept { 
    if (--_nrQueued == UINT64_MAX) {
      TRI_ASSERT(false);
    }
  }
 
 private:
  void startNewThread();
 
  static void initializeSignalHandlers();

 private:
  // we store most of the threads status info in a single atomic uint64_t
  // the encoding of the values inside this variable is (left to right means
  // high to low bytes):
  // 
  //   AA BB CC DD
  // 
  // we use the lowest 2 bytes (DD) to store the number of running threads
  // the next lowest bytes (CC) are used to store the number of currently working threads
  // the next bytes (BB) are used to store the number of currently blocked threads
  // the highest bytes (AA) are used only to encode a stopping bit. when this bit is
  // set, the scheduler is stopping (or already stopped)
  inline void setStopping() noexcept { _counters |= (1ULL << 63); }

  inline void incRunning() noexcept { _counters += 1ULL << 0; }
  inline void decRunning() noexcept { _counters -= 1ULL << 0; }

  inline void workThread() noexcept { _counters += 1ULL << 16; } 
  inline void unworkThread() noexcept { _counters -= 1ULL << 16; }

  inline void blockThread() noexcept { _counters += 1ULL << 32; }
  inline void unblockThread() noexcept { _counters -= 1ULL << 32; }

  inline uint64_t numRunning(uint64_t value) const noexcept { return value & 0xFFFFULL; }
  inline uint64_t numWorking(uint64_t value) const noexcept { return (value >> 16) & 0xFFFFULL; }
  inline uint64_t numBlocked(uint64_t value) const noexcept { return (value >> 32) & 0xFFFFULL; }
  inline bool isStopping(uint64_t value) const noexcept { return (value & (1ULL << 63)) != 0; }

  void startIoService();
  void startRebalancer();
  void startManagerThread();
  void rebalanceThreads();

 private:
  // maximal number of outstanding user requests
  uint64_t const _maxQueueSize;

  // minimum number of running SchedulerThreads
  uint64_t const _nrMinimum;

  // maximal number of outstanding user requests
  uint64_t const _nrMaximum;

  // current counters. refer to the above description of the 
  // meaning of its individual bits
  std::atomic<uint64_t> _counters;

  // number of jobs that are currently been queued, but not worked on
  std::atomic<uint64_t> _nrQueued;

  std::unique_ptr<JobQueue> _jobQueue;

  boost::shared_ptr<boost::asio::io_service::work> _serviceGuard;
  std::unique_ptr<boost::asio::io_service> _ioService;

  boost::shared_ptr<boost::asio::io_service::work> _managerGuard;
  std::unique_ptr<boost::asio::io_service> _managerService;

  std::unique_ptr<boost::asio::steady_timer> _threadManager;
  std::function<void(const boost::system::error_code&)> _threadHandler;

  mutable Mutex _threadCreateLock;
  double _lastAllBusyStamp;
};
}
}

#endif