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Lunar Base is a simple game framework written in Java. It is written using an entity-component-system architecture.

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/*
 * This file is part of the lunar-base package.
 *
 * Copyright (c) 2014 Eric Fritz
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
 * and associated documentation files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all copies or
 * substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING
 * BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
 * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

package com.kauridev.lunarbase;

import java.util.LinkedList;
import java.util.Queue;

/**
 * A manager that handles the creation and destruction of entities.
 *
 * @author Eric Fritz
 */
public class EntityManager
{
	/**
	 * The event manager.
	 */
	private EventManager eventManager;

	/**
	 * A unique incrementing id for new entities.
	 */
	private int uniqueId;

	/**
	 * A list of entities that may be re-used.
	 */
	private Queue pool = new LinkedList<>();

	/**
	 * Creates a new EntityManager.
	 *
	 * @param eventManager The event manager.
	 */
	public EntityManager(EventManager eventManager) {
		this.eventManager = eventManager;
	}

	/**
	 * Creates a new entity. This method fires the {@link EntityCreatedEvent} event.
	 *
	 * @return A new entity.
	 */
	public Entity create() {
		Entity entity = pool.poll();

		if (entity == null) {
			entity = new Entity(uniqueId++);
		}

		eventManager.dispatch(new EntityCreatedEvent(entity));
		return entity;
	}

	/**
	 * Removes an entity. This method fires the {@link EntityRemovedEvent} event.
	 *
	 * @param entity The entity to remove.
	 */
	public void remove(Entity entity) {
		pool.add(entity);
		eventManager.dispatch(new EntityRemovedEvent(entity));
	}
}