////////////////////////////////////////////////////////////////////////////////
/// 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 Daniel H. Larkin
////////////////////////////////////////////////////////////////////////////////

#ifndef ARANGODB_BASICS_LOCAL_TASK_QUEUE_H
#define ARANGODB_BASICS_LOCAL_TASK_QUEUE_H 1

#include <memory>
#include <queue>

#include "Basics/Common.h"
#include "Basics/ConditionVariable.h"
#include "Basics/Mutex.h"

namespace arangodb {
namespace basics {

class LocalTaskQueue;

class LocalTask : public std::enable_shared_from_this<LocalTask> {
 public:
  LocalTask() = delete;
  LocalTask(LocalTask const&) = delete;
  LocalTask& operator=(LocalTask const&) = delete;

  explicit LocalTask(std::shared_ptr<LocalTaskQueue> const& queue);
  virtual ~LocalTask() {}

  virtual void run() = 0;
  void dispatch();

 protected:
  //////////////////////////////////////////////////////////////////////////////
  /// @brief the underlying queue
  //////////////////////////////////////////////////////////////////////////////

  std::shared_ptr<LocalTaskQueue> _queue;
};

class LocalCallbackTask : public std::enable_shared_from_this<LocalCallbackTask> {
 public:
  LocalCallbackTask() = delete;
  LocalCallbackTask(LocalCallbackTask const&) = delete;
  LocalCallbackTask& operator=(LocalCallbackTask const&) = delete;

  LocalCallbackTask(std::shared_ptr<LocalTaskQueue> const& queue,
                    std::function<void()> const& cb);
  virtual ~LocalCallbackTask() {}

  virtual void run();
  void dispatch();

 protected:
  //////////////////////////////////////////////////////////////////////////////
  /// @brief the underlying queue
  //////////////////////////////////////////////////////////////////////////////

  std::shared_ptr<LocalTaskQueue> _queue;

  //////////////////////////////////////////////////////////////////////////////
  /// @brief the callback executed by run() (any exceptions will be caught and
  /// ignored; must not call queue->setStatus() or queue->enqueue())
  //////////////////////////////////////////////////////////////////////////////

  std::function<void()> _cb;
};

class LocalTaskQueue {
 public:
  typedef std::function<void(std::function<void()>)> PostFn;

  LocalTaskQueue() = delete;
  LocalTaskQueue(LocalTaskQueue const&) = delete;
  LocalTaskQueue& operator=(LocalTaskQueue const&) = delete;

  explicit LocalTaskQueue(PostFn poster);

  ~LocalTaskQueue();

  void startTask();
  void stopTask();

  //////////////////////////////////////////////////////////////////////////////
  /// @brief enqueue a task to be run
  //////////////////////////////////////////////////////////////////////////////

  void enqueue(std::shared_ptr<LocalTask>);

  //////////////////////////////////////////////////////////////////////////////
  /// @brief enqueue a callback task to be run after all normal tasks finish;
  /// useful for cleanup tasks
  //////////////////////////////////////////////////////////////////////////////

  void enqueueCallback(std::shared_ptr<LocalCallbackTask>);

  //////////////////////////////////////////////////////////////////////////////
  /// @brief post a function to the scheduler. Should only be used internally
  /// by task dispatch.
  //////////////////////////////////////////////////////////////////////////////

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

  //////////////////////////////////////////////////////////////////////////////
  /// @brief join a single task. reduces the number of waiting tasks and wakes
  /// up the queues's dispatchAndWait() routine
  //////////////////////////////////////////////////////////////////////////////

  void join();

  //////////////////////////////////////////////////////////////////////////////
  /// @brief dispatch all tasks, including those that are queued while running,
  /// and wait for all tasks to join; then dispatch all callback tasks and wait
  /// for them to join
  //////////////////////////////////////////////////////////////////////////////

  void dispatchAndWait();

  //////////////////////////////////////////////////////////////////////////////
  /// @brief set status of queue
  //////////////////////////////////////////////////////////////////////////////

  void setStatus(int);

  //////////////////////////////////////////////////////////////////////////////
  /// @brief return overall status of queue tasks
  //////////////////////////////////////////////////////////////////////////////

  int status();

 private:
  //////////////////////////////////////////////////////////////////////////////
  /// @brief post task to scheduler/io_service
  //////////////////////////////////////////////////////////////////////////////

  PostFn _poster;

  //////////////////////////////////////////////////////////////////////////////
  /// @brief internal task queue
  //////////////////////////////////////////////////////////////////////////////

  std::queue<std::shared_ptr<LocalTask>> _queue;

  //////////////////////////////////////////////////////////////////////////////
  /// @brief internal callback task queue
  //////////////////////////////////////////////////////////////////////////////

  std::queue<std::shared_ptr<LocalCallbackTask>> _callbackQueue;

  //////////////////////////////////////////////////////////////////////////////
  /// @brief condition variable
  //////////////////////////////////////////////////////////////////////////////

  arangodb::basics::ConditionVariable _condition;

  //////////////////////////////////////////////////////////////////////////////
  /// @brief internal mutex
  //////////////////////////////////////////////////////////////////////////////

  Mutex _mutex;

  //////////////////////////////////////////////////////////////////////////////
  /// @brief number of dispatched, non-joined tasks
  //////////////////////////////////////////////////////////////////////////////

  size_t _missing;

  //////////////////////////////////////////////////////////////////////////////
  /// @brief number of dispatched and started tasks
  //////////////////////////////////////////////////////////////////////////////

  size_t _started;

  //////////////////////////////////////////////////////////////////////////////
  /// @brief overall status of queue tasks
  //////////////////////////////////////////////////////////////////////////////

  int _status;
};

}  // namespace basics
}  // namespace arangodb

#endif