/*
	PIP - Platform Independent Primitives
	
	Stephan Fomenko

	This program is free software: you can redistribute it and/or modify
	it under the terms of the GNU Lesser General Public License as published by
	the Free Software Foundation, either version 3 of the License, or
	(at your option) any later version.

	This program is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
	GNU Lesser General Public License for more details.

	You should have received a copy of the GNU Lesser General Public License
	along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#ifndef PIP_EXECUTOR_H
#define PIP_EXECUTOR_H

#include "piblockingdequeue.h"
#include <atomic>

/**
 * @brief Thread pools address two different problems: they usually provide improved performance when executing large
 * numbers of asynchronous tasks, due to reduced per-task invocation overhead, and they provide a means of bounding and
 * managing the resources, including threads, consumed when executing a collection of tasks.
 *
 * TODO adapt documentation to template
 */
template <typename Thread_, typename Dequeue_>
class PIP_EXPORT PIThreadPoolExecutorTemplate {
public:
	explicit PIThreadPoolExecutorTemplate(size_t corePoolSize = 1) : isShutdown_(false) { makePool(corePoolSize); }

	virtual ~PIThreadPoolExecutorTemplate() {
		shutdownNow();
		while (threadPool.size() > 0) delete threadPool.take_back();
	}

	/**
	 * @brief Executes the given task sometime in the future. The task execute in an existing pooled thread. If the task
	 * cannot be submitted for execution, either because this executor has been shutdown or because its capacity has been
	 * reached.
	 *
	 * @param runnable not empty function for thread pool execution
	 */
	void execute(const std::function<void()> & runnable) {
		if (!isShutdown_) taskQueue.offer(runnable);
	}

	/**
	 * @brief Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be
	 * accepted. Invocation has no additional effect if already shut down. This method does not wait for previously
	 * submitted tasks to complete execution. Use awaitTermination to do that.
	 */
	void shutdown() {
		isShutdown_ = true;
	}

	void shutdownNow() {
		isShutdown_ = true;
		for (size_t i = 0; i < threadPool.size(); ++i) threadPool[i]->stop();
	}

	bool isShutdown() const {
		return isShutdown_;
	}

	bool awaitTermination(int timeoutMs) {
		PITimeMeasurer measurer;
		for (size_t i = 0; i < threadPool.size(); ++i) {
			int dif = timeoutMs - (int)measurer.elapsed_m();
			if (dif < 0) return false;
			if (!threadPool[i]->waitForFinish(dif)) return false;
		}
		return true;
	}

protected:
	std::atomic_bool isShutdown_;
	Dequeue_ taskQueue;
	PIVector<Thread_*> threadPool;

	template<typename Function>
	PIThreadPoolExecutorTemplate(size_t corePoolSize, Function onBeforeStart) : isShutdown_(false) {
		makePool(corePoolSize, onBeforeStart);
	}

	void makePool(size_t corePoolSize, std::function<void(Thread_*)> onBeforeStart = [](Thread_*){}) {
		for (size_t i = 0; i < corePoolSize; ++i) {
			auto* thread = new Thread_([&, i](){
				auto runnable = taskQueue.poll(100);
				if (runnable) {
					runnable();
				}
				if (isShutdown_ && taskQueue.size() == 0) threadPool[i]->stop();
			});
			threadPool.push_back(thread);
			onBeforeStart(thread);
			thread->start();
		}
	}
};

typedef PIThreadPoolExecutorTemplate<PIThread, PIBlockingDequeue<std::function<void()> > > PIThreadPoolExecutor;


#endif //PIP_EXECUTOR_H