/***

  Olive - Non-Linear Video Editor
  Copyright (C) 2022 Olive Team
  Modifications Copyright (C) 2025 mikesolar

  This program is free software: you can redistribute it and/or modify
  it under the terms of the GNU 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 General Public License for more details.

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

***/

#ifndef OAK_TASKMANAGER_H
#define OAK_TASKMANAGER_H

#include <QtConcurrent/QtConcurrent>
#include <QVector>
#include <QUndoCommand>

#include "task/task.h"

namespace olive
{

/**
 * @brief An object that manages background Task objects, handling their start and end
 *
 * TaskManager handles the life of a Task object. After a new Task is created, it should be sent to TaskManager through
 * AddTask(). TaskManager will take ownership of the task and add it to a queue until it system resources are available
 * for it to run. Currently, TaskManager will run no more Tasks than there are threads on the system (one task per
 * thread). As Tasks finished, TaskManager will start the next in the queue.
 */
class TaskManager : public QObject {
	Q_OBJECT
public:
	/**
   * @brief TaskManager Constructor
   */
	TaskManager();

	/**
   * @brief TaskManager Destructor
   *
   * Ensures all Tasks are deleted
   */
	virtual ~TaskManager();

	static void create_instance();

	static void destroy_instance();

	static TaskManager *instance();

	int get_task_count() const;

	Task *get_first_task() const;

	void cancel_task_and_wait(Task *t);

public slots:
	/**
   * @brief Add a new Task
   *
   * Adds a new Task to the queue. If there are available threads to run it, it'll also run immediately. Otherwise,
   * it'll be placed into the queue and run when resources are available.
   *
   * NOTE: This function is NOT thread-safe and is currently intended to only be used from the main/GUI thread.
   *
   * NOTE: A Task object should only be added once. Adding the same Task object more than once will result in undefined
   * behavior.
   *
   * @param t
   *
   * The task to add and run. TaskManager takes ownership of this Task and will be responsible for freeing it.
   */
	void add_task(Task *t);

	void cancel_task(Task *t);

signals:
	/**
   * @brief Signal emitted when a Task is added by AddTask()
   *
   * @param t
   *
   * Task that was added
   */
	void task_added(Task *t);

	/**
   * @brief Signal emitted when any change to the running task list has been made
   */
	void task_list_changed();

	/**
   * @brief Signal emitted when a task is deleted
   */
	void task_removed(Task *t);

	/**
   * @brief Signal emitted when a task fails
   */
	void task_failed(Task *t);

private:
	/**
   * @brief Internal task array
   */
	QHash<QFutureWatcher<bool> *, Task *> tasks_;

	/**
   * @brief Internal list of failed tasks
   */
	std::list<Task *> failed_tasks_;

	/**
   * @brief Task thread pool
   */
	QThreadPool thread_pool_;

	/**
   * @brief TaskManager singleton instance_
   */
	static TaskManager *instance_;

private slots:
	void task_finished();
};

}

#endif // OAK_TASKMANAGER_H