/*******************************************************************************
 * Copyright 2014 See AUTHORS file.
 * 
 * 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.
 ******************************************************************************/

package com.badlogic.ashley.systems;

import com.badlogic.ashley.core.Engine;
import com.badlogic.ashley.core.Entity;
import com.badlogic.ashley.core.EntitySystem;
import com.badlogic.ashley.core.Family;
import com.badlogic.ashley.utils.ImmutableArray;

/**
 * A simple EntitySystem that iterates over each entity and calls processEntity() for each entity every time the EntitySystem is
 * updated. This is really just a convenience class as most systems iterate over a list of entities.
 * @author Stefan Bachmann
 */
public abstract class IteratingSystem extends EntitySystem {
	private Family family;
	private ImmutableArray<Entity> entities;

	/**
	 * Instantiates a system that will iterate over the entities described by the Family.
	 * @param family The family of entities iterated over in this System
	 */
	public IteratingSystem (Family family) {
		this(family, 0);
	}

	/**
	 * Instantiates a system that will iterate over the entities described by the Family, with a specific priority.
	 * @param family The family of entities iterated over in this System
	 * @param priority The priority to execute this system with (lower means higher priority)
	 */
	public IteratingSystem (Family family, int priority) {
		super(priority);

		this.family = family;
	}

	@Override
	public void addedToEngine (Engine engine) {
		entities = engine.getEntitiesFor(family);
	}

	@Override
	public void removedFromEngine (Engine engine) {
		entities = null;
	}

	@Override
	public void update (float deltaTime) {
		for (int i = 0; i < entities.size(); ++i) {
			processEntity(entities.get(i), deltaTime);
		}
	}

	/**
	 * @return set of entities processed by the system
	 */
	public ImmutableArray<Entity> getEntities () {
		return entities;
	}

	/**
	 * @return the Family used when the system was created
	 */
	public Family getFamily () {
		return family;
	}

	/**
	 * This method is called on every entity on every update call of the EntitySystem. Override this to implement your system's
	 * specific processing.
	 * @param entity The current Entity being processed
	 * @param deltaTime The delta time between the last and current frame
	 */
	protected abstract void processEntity (Entity entity, float deltaTime);
}