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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.Collections;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.Set;

/**
 * A collection of entities which specify a given criteria. This collection keeps itself current by
 * listening to entity changed and removed events. If an entity receives a property which allows it
 * to be in the collection, it is added automatically. If an entity removes a property which allows
 * it to be in the collection, it is removed automatically.
 * 
 * The criteria by which an entity is allowed in the collection is determined by an entity matcher.
 * Entity matchers may be composed for greater flexibility.
 *
 * @author Eric Fritz
 */
public class EntityCollection implements Iterable, EntityChangedEventListener, EntityRemovedEventListener
{
	/**
	 * The entity matcher.
	 */
	private EntityMatcher matcher;

	/**
	 * The wrapped entity list.
	 */
	private Set actives = new LinkedHashSet<>();

	/**
	 * Creates a new EntityCollection.
	 *
	 * @param eventManager The event manager.
	 * @param matcher      The entity matcher.
	 */
	public EntityCollection(EventManager eventManager, EntityMatcher matcher) {
		this.matcher = matcher;

		eventManager.addListener(EntityChangedEvent.class, this);
		eventManager.addListener(EntityRemovedEvent.class, this);
	}

	@Override
	public Iterator iterator() {
		return Collections.unmodifiableSet(actives).iterator();
	}

	@Override
	public EntityChangedEvent onEntityChanged(EntityChangedEvent event) {
		Entity entity = event.getEntity();

		if (matcher.matches(entity)) {
			actives.add(entity);
		} else {
			actives.remove(entity);
		}

		return event;
	}

	@Override
	public EntityRemovedEvent onEntityRemoved(EntityRemovedEvent event) {
		actives.remove(event.getEntity());
		return event;
	}
}