// Copyright 2020 Google LLC
//
// 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
//
//     https://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.

#ifndef PLATFORM_IMPL_WINDOWS_THREAD_POOL_H_
#define PLATFORM_IMPL_WINDOWS_THREAD_POOL_H_

#include <windows.h>

#include <queue>
#include <utility>

#include "absl/synchronization/mutex.h"
#include "internal/platform/runnable.h"

namespace location {
namespace nearby {
namespace windows {

class ThreadPool {
 public:
  virtual ~ThreadPool();
  static std::unique_ptr<ThreadPool> Create(int max_pool_size);

  // Runs a task on thread pool. The result indicates whether the task is put
  // into the thread pool.
  bool Run(Runnable task);

  // The thread pool is closed immediately if there are no outstanding work,
  // I/O, timer, or wait objects that are bound to the pool; otherwise, the
  // thread pool is released asynchronously after the outstanding objects are
  // freed.
  void ShutDown();

 private:
  ThreadPool(PTP_POOL thread_pool, TP_CALLBACK_ENVIRON thread_pool_environ,
             int max_pool_size);
  void RunNextTask();

  // Protects the access to tasks of the thread pool.
  mutable absl::Mutex mutex_;

  // The task queue of the thread pool. Thread pool will pick up task to run
  // when it is idle.
  std::queue<Runnable> tasks_ ABSL_GUARDED_BY(mutex_);

  // Keeps the pointer of the thread pool. It is created when constructing the
  // thread pool.
  PTP_POOL thread_pool_ = nullptr;

  // Keeps the environment of the thread pool.
  TP_CALLBACK_ENVIRON thread_pool_environ_;

  // The maximum thread count in the thread pool
  int max_pool_size_ = 0;

  friend VOID CALLBACK WorkCallback(PTP_CALLBACK_INSTANCE instance,
                                    PVOID parameter, PTP_WORK work);
};

}  // namespace windows
}  // namespace nearby
}  // namespace location

#endif  //  PLATFORM_IMPL_WINDOWS_THREAD_POOL_H_