/*
 * Copyright 2007-2013
 * Licensed under GNU Lesser General Public License
 * 
 * This file is part of EpochX
 * 
 * EpochX is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 * 
 * EpochX 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 Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public License
 * along with EpochX. If not, see <http://www.gnu.org/licenses/>.
 * 
 * The latest version is available from: http://www.epochx.org
 */

package org.epochx.selection;

import org.epochx.Config;
import org.epochx.Config.ConfigKey;
import org.epochx.Individual;
import org.epochx.IndividualSelector;
import org.epochx.Population;

/**
 * This class represents an {@link IndividualSelector} that selects individuals
 * through a tournament performed on a subset of the population. In tournament
 * selection, <code>n</code> individuals are randomly selected and the
 * individual with the highest fitness is considered the winner of the
 * tournament and becomes the selected individual.
 */
public class TournamentSelector implements IndividualSelector {

	/**
	 * The key for setting and retrieving the tournament size.
	 */
	public static final ConfigKey<Integer> TOURNAMENT_SIZE = new ConfigKey<Integer>();

	/**
	 * The random selector used to select the individuals participating in the
	 * tournament.
	 */
	private final RandomSelector randomSelector;

	/**
	 * The tournament size.
	 */
	private int size;

	/**
	 * Constructs a <code>TournamentSelector</code>.
	 */
	public TournamentSelector() {
		randomSelector = new RandomSelector();
	}

	@Override
	public void setup(Population population) {
		randomSelector.setup(population);
		size = Config.getInstance().get(TOURNAMENT_SIZE);
	}

	/**
	 * Returns the selected individual using a tournament.
	 * 
	 * @return the selected individual using a tournament.
	 */
	@Override
	public Individual select() {
		Individual best = null;

		// choose and compare randomly selected programs.
		for (int i = 0; i < size; i++) {
			Individual individual = randomSelector.select();
			if ((best == null) || (individual.compareTo(best) > 0)) {
				best = individual;
			}
		}

		return best;
	}

}