/*
 * Copyright 2007-2011 Tom Castle & Lawrence Beadle
 * Licensed under GNU Lesser General Public License
 * 
 * This file is part of EpochX: genetic programming software for research
 * 
 * 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.epox;

import org.epochx.tools.random.RandomNumberGenerator;

/**
 * Defines an integer ephemeral random constant (ERC). An ERC is a literal with
 * a value which is randomly generated upon construction. This implementation
 * will generate an integer between the lower and upper bounds provided. All
 * values between the two bounds (inclusive), can appear with equal probability.
 * As with all nodes, instances may be constructed in any of 3 ways:
 * <ul>
 * <li>constructor - the new instance will be initialised with a value of
 * <code>null</code>.</li>
 * <li>clone method - will return an instance with a value equal to the cloned
 * value.</li>
 * <li>newInstance method - will return a new instance with a new, randomly
 * generated value.</li>
 * </ul>
 * 
 * @see BooleanERC
 * @see DoubleERC
 */
public class IntegerERC extends Literal {

	private RandomNumberGenerator rng;

	// The inclusive bounds.
	private int upper;
	private int lower;

	/**
	 * Constructs a new <code>IntegerERC</code> with a value of
	 * <code>null</code>. The given random number generator will be be used to
	 * generate a new value if the <code>newInstance</code> method is used.
	 * 
	 * @param rng the random number generator to use if randomly generating an
	 *        integer value.
	 * @param lower the inclusive lower bound of values that are generated.
	 * @param upper the inclusive upper bound of values that are generated.
	 */
	public IntegerERC(final RandomNumberGenerator rng, final int lower, final int upper) {
		super(null);
		
		
		if (rng == null) {
			throw new IllegalArgumentException("random generator must not be null");
		}

		this.rng = rng;
		this.lower = lower;
		this.upper = upper;
		
		// Set its value.
		setValue(generateValue());
	}

	/**
	 * Constructs a new <code>IntegerERC</code> node with a randomly generated
	 * value, selected using the random number generator. The value will be
	 * randomly selected with an equal probability from the set of values
	 * between the lower and upper bounds.
	 * 
	 * @return a new <code>IntegerERC</code> instance with a randomly generated
	 *         value.
	 */
	@Override
	public IntegerERC newInstance() {
		final IntegerERC erc = (IntegerERC) super.newInstance();

		erc.setValue(generateValue());

		return erc;
	}

	/**
	 * Generates and returns a new integer value for use in a new
	 * <code>IntegerERC</code> instance. This implementation will return a value
	 * selected randomly from the set of values between the lower and upper
	 * bounds, inclusively.
	 * 
	 * @return an integer value to be used as the value of a new IntegerERC
	 *         instance.
	 */
	protected int generateValue() {
		if (rng == null) {
			throw new IllegalStateException("random number generator must not be null");
		}

		final int range = upper - lower;
		return (rng.nextInt(range) + lower);
	}

	/**
	 * Returns the random number generator that is currently being used to
	 * generate integer values for new <code>IntegerERC</code> instances.
	 * 
	 * @return the random number generator
	 */
	public RandomNumberGenerator getRNG() {
		return rng;
	}

	/**
	 * Sets the random number generator to be used for generating the integer
	 * value of new <code>IntegerERC</code> instances.
	 * 
	 * @param rng the random number generator to set
	 */
	public void setRNG(final RandomNumberGenerator rng) {
		this.rng = rng;
	}

	/**
	 * Returns the lower bound of the newly generated values.
	 * 
	 * @return the lower bound of values.
	 */
	public int getLower() {
		return lower;
	}

	/**
	 * Sets the inclusive lower bound for newly generated values.
	 * 
	 * @param lower the lower bound for values.
	 */
	public void setLower(final int lower) {
		this.lower = lower;
	}

	/**
	 * Returns the upper bound of the newly generated values.
	 * 
	 * @return the upper bound of values.
	 */
	public int getUpper() {
		return upper;
	}

	/**
	 * Sets the inclusive upper bound for newly generated values.
	 * 
	 * @param upper the upper bound for values.
	 */
	public void setUpper(final int upper) {
		this.upper = upper;
	}
}
