/*
  Copyright (c) 2019 Sogou, Inc.

  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.

  Author: Xie Han (xiehan@sogou-inc.com)
*/

#ifndef _WORKFLOW_H_
#define _WORKFLOW_H_

#include <assert.h>
#include <stddef.h>
#include <utility>
#include <functional>
#include <mutex>
#include "SubTask.h"

class SeriesWork;
class ParallelWork;

using series_callback_t = std::function<void (const SeriesWork *)>;
using parallel_callback_t = std::function<void (const ParallelWork *)>;

class Workflow
{
public:
	static SeriesWork *
	create_series_work(SubTask *first, series_callback_t callback);

	static void
	start_series_work(SubTask *first, series_callback_t callback);

	static ParallelWork *
	create_parallel_work(parallel_callback_t callback);

	static ParallelWork *
	create_parallel_work(SeriesWork *const all_series[], size_t n,
						 parallel_callback_t callback);

	static void
	start_parallel_work(SeriesWork *const all_series[], size_t n,
						parallel_callback_t callback);

public:
	static SeriesWork *
	create_series_work(SubTask *first, SubTask *last,
					   series_callback_t callback);

	static void
	start_series_work(SubTask *first, SubTask *last,
					  series_callback_t callback);
};

class SeriesWork
{
public:
	void start()
	{
		assert(!this->in_parallel);
		this->first->dispatch();
	}

	/* Call dismiss() only when you don't want to start a created series.
	 * This operation is recursive, so only call on the "root". */
	void dismiss()
	{
		assert(!this->in_parallel);
		this->dismiss_recursive();
	}

public:
	void push_back(SubTask *task);
	void push_front(SubTask *task);

public:
	void *get_context() const { return this->context; }
	void set_context(void *context) { this->context = context; }

public:
	/* Cancel a running series. Typically, called in the callback of a task
	 * that belongs to the series. All subsequent tasks in the series will be
	 * destroyed immediately and recursively (ParallelWork), without callback.
	 * But the callback of this canceled series will still be called. */
	virtual void cancel() { this->canceled = true; }

	/* Parallel work's callback may check the cancellation state of each
	 * sub-series, and cancel it's super-series recursively. */
	bool is_canceled() const { return this->canceled; }

	/* 'false' until the time of callback. Mainly for sub-class. */
	bool is_finished() const { return this->finished; }

public:
	void set_callback(series_callback_t callback)
	{
		this->callback = std::move(callback);
	}

public:
	virtual void *get_specific(const char *key) { return NULL; }

public:
	/* The following functions are intended for task implementations only. */
	SubTask *pop();

	SubTask *get_last_task() const { return this->last; }

	void set_last_task(SubTask *last)
	{
		last->set_pointer(this);
		this->last = last;
	}

	void unset_last_task() { this->last = NULL; }

	const ParallelTask *get_in_parallel() const { return this->in_parallel; }

protected:
	void set_in_parallel(const ParallelTask *task) { this->in_parallel = task; }

	void dismiss_recursive();

protected:
	void *context;
	series_callback_t callback;

private:
	SubTask *pop_task();
	void expand_queue();

private:
	SubTask *buf[4];
	SubTask *first;
	SubTask *last;
	SubTask **queue;
	int queue_size;
	int front;
	int back;
	bool canceled;
	bool finished;
	const ParallelTask *in_parallel;
	std::mutex mutex;

protected:
	SeriesWork(SubTask *first, series_callback_t&& callback);
	virtual ~SeriesWork();
	friend class ParallelWork;
	friend class Workflow;
};

static inline SeriesWork *series_of(const SubTask *task)
{
	return (SeriesWork *)task->get_pointer();
}

static inline SeriesWork& operator *(const SubTask& task)
{
	return *series_of(&task);
}

static inline SeriesWork& operator << (SeriesWork& series, SubTask *task)
{
	series.push_back(task);
	return series;
}

inline SeriesWork *
Workflow::create_series_work(SubTask *first, series_callback_t callback)
{
	return new SeriesWork(first, std::move(callback));
}

inline void
Workflow::start_series_work(SubTask *first, series_callback_t callback)
{
	new SeriesWork(first, std::move(callback));
	first->dispatch();
}

inline SeriesWork *
Workflow::create_series_work(SubTask *first, SubTask *last,
							 series_callback_t callback)
{
	SeriesWork *series = new SeriesWork(first, std::move(callback));
	series->set_last_task(last);
	return series;
}

inline void
Workflow::start_series_work(SubTask *first, SubTask *last,
							series_callback_t callback)
{
	SeriesWork *series = new SeriesWork(first, std::move(callback));
	series->set_last_task(last);
	first->dispatch();
}

class ParallelWork : public ParallelTask
{
public:
	void start()
	{
		assert(!series_of(this));
		Workflow::start_series_work(this, nullptr);
	}

	void dismiss()
	{
		assert(!series_of(this));
		delete this;
	}

public:
	void add_series(SeriesWork *series);

public:
	void *get_context() const { return this->context; }
	void set_context(void *context) { this->context = context; }

public:
	SeriesWork *series_at(size_t index)
	{
		if (index < this->subtasks_nr)
			return this->all_series[index];
		else
			return NULL;
	}

	const SeriesWork *series_at(size_t index) const
	{
		if (index < this->subtasks_nr)
			return this->all_series[index];
		else
			return NULL;
	}

	SeriesWork& operator[] (size_t index)
	{
		return *this->series_at(index);
	}

	const SeriesWork& operator[] (size_t index) const
	{
		return *this->series_at(index);
	}

	size_t size() const { return this->subtasks_nr; }

public:
	void set_callback(parallel_callback_t callback)
	{
		this->callback = std::move(callback);
	}

protected:
	virtual SubTask *done();

protected:
	void *context;
	parallel_callback_t callback;

private:
	void expand_buf();

private:
	size_t buf_size;
	SeriesWork **all_series;

protected:
	ParallelWork(parallel_callback_t&& callback);
	ParallelWork(SeriesWork *const all_series[], size_t n,
				 parallel_callback_t&& callback);
	virtual ~ParallelWork();
	friend class Workflow;
};

inline ParallelWork *
Workflow::create_parallel_work(parallel_callback_t callback)
{
	return new ParallelWork(std::move(callback));
}

inline ParallelWork *
Workflow::create_parallel_work(SeriesWork *const all_series[], size_t n,
							   parallel_callback_t callback)
{
	return new ParallelWork(all_series, n, std::move(callback));
}

inline void
Workflow::start_parallel_work(SeriesWork *const all_series[], size_t n,
							  parallel_callback_t callback)
{
	ParallelWork *p = new ParallelWork(all_series, n, std::move(callback));
	Workflow::start_series_work(p, nullptr);
}

#endif