/*
 *  Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may
 *  be found in the AUTHORS file in the root of the source tree.
 */
#ifndef WEBRTC_TEST_SINGLE_THREADED_TASK_QUEUE_H_
#define WEBRTC_TEST_SINGLE_THREADED_TASK_QUEUE_H_

#include <functional>
#include <list>
#include <memory>

#include "webrtc/rtc_base/criticalsection.h"
#include "webrtc/rtc_base/event.h"
#include "webrtc/rtc_base/platform_thread.h"
#include "webrtc/rtc_base/thread_checker.h"

namespace webrtc {
namespace test {

// This class gives capabilities similar to rtc::TaskQueue, but ensures
// everything happens on the same thread. This is intended to make the
// threading model of unit-tests (specifically end-to-end tests) more closely
// resemble that of real WebRTC, thereby allowing us to replace some critical
// sections by thread-checkers.
// This task is NOT tuned for performance, but rather for simplicity.
class SingleThreadedTaskQueueForTesting {
 public:
  using Task = std::function<void()>;
  using TaskId = size_t;

  explicit SingleThreadedTaskQueueForTesting(const char* name);
  ~SingleThreadedTaskQueueForTesting();

  // Sends one task to the task-queue, and returns a handle by which the
  // task can be cancelled.
  // This mimics the behavior of TaskQueue, but only for lambdas, rather than
  // for both lambdas and QueuedTask objects.
  TaskId PostTask(Task task);

  // Same as PostTask(), but ensures that the task will not begin execution
  // less than |delay_ms| milliseconds after being posted; an upper bound
  // is not provided.
  TaskId PostDelayedTask(Task task, int64_t delay_ms);

  // Send one task to the queue. The function does not return until the task
  // has finished executing. No support for canceling the task.
  void SendTask(Task task);

  // Given an identifier to the task, attempts to eject it from the queue.
  // Returns true if the task was found and cancelled. Failure possible
  // only for invalid task IDs, or for tasks which have already been executed.
  bool CancelTask(TaskId task_id);

 private:
  struct QueuedTask {
    QueuedTask(TaskId task_id, int64_t earliest_execution_time, Task task);
    ~QueuedTask();

    TaskId task_id;
    int64_t earliest_execution_time;
    Task task;
  };

  static void Run(void* obj);

  void RunLoop();

  rtc::CriticalSection cs_;
  std::list<std::unique_ptr<QueuedTask>> tasks_ GUARDED_BY(cs_);
  rtc::ThreadChecker owner_thread_checker_;
  rtc::PlatformThread thread_;
  bool running_ GUARDED_BY(cs_);

  TaskId next_task_id_;

  // The task-queue will sleep when not executing a task. Wake up occurs when:
  // * Upon destruction, to make sure that the |thead_| terminates, so that it
  //   may be joined. [Event will be set.]
  // * New task added. Because we optimize for simplicity rahter than for
  //   performance (this class is a testing facility only), waking up occurs
  //   when we get a new task even if it is scheduled with a delay. The RunLoop
  //   is in charge of sending itself back to sleep if the next task is only
  //   to be executed at a later time. [Event will be set.]
  // * When the next task in the queue is a delayed-task, and the time for
  //   its execution has come. [Event will time-out.]
  rtc::Event wake_up_;
};

}  // namespace test
}  // namespace webrtc

#endif  // WEBRTC_TEST_SINGLE_THREADED_TASK_QUEUE_H_