/*
 * Copyright 2007-2013
 * 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.bool;

import org.epochx.epox.Node;
import org.epochx.tools.DataTypeUtils;

/**
 * A node which performs the logical operation of <code>NAND</code>, which is 
 * equivalent to the negation of the conjunction, <code>NOT AND</code>
 * 
 * @since 2.0
 */
public class Nand extends Node {

    public static final String IDENTIFIER = "NAND";

	/**
	 * Constructs a <code>NandFunction</code> with two <code>null</code> children
	 */
	public Nand() {
		this(null, null);
	}

	/**
	 * Constructs a <code>NandFunction</code> with two boolean child nodes
	 * 
	 * @param child1 the first child node
	 * @param child2 the second child node
	 */
	public Nand(Node child1, Node child2) {
		super(child1, child2);
	}

	/**
	 * Evaluates this function lazily. The first child node is evaluated, the
	 * result of which must be a <code>Boolean</code> instance. The second child
	 * is only evaluated if the first had a <code>true</code> value. The result of 
	 * this method will be <code>true</code> if both children evaluate to 
	 * <code>false</code>, otherwise it will return <code>false</code>.
	 * 
	 * @return <code>true</code> if both children evaluate to <code>false</code> 
	 * 			otherwise <code>false</code> is returned
	 */
	@Override
	public Boolean evaluate() {
		boolean result = ((Boolean) getChild(0).evaluate()).booleanValue();

		if (result) {
			result = ((Boolean) getChild(1).evaluate()).booleanValue();
		}

		return !result;
	}

	/**
	 * Returns the identifier of this function which is <code>NAND</code>
	 * 
	 * @return this node's identifier
	 */
	@Override
	public String getIdentifier() {
		return IDENTIFIER;
	}

	/**
	 * Returns this function node's return type for the given child input types.
	 * If there are two children, both of which have a return type of 
	 * <code>Boolean</code>, then the return type of this function will also be 
	 * <code>Boolean</code>. In all other cases this method will return 
	 * <code>null</code> to indicate that the inputs are invalid.
	 * 
	 * @return The Boolean class or null if the input type is invalid.
	 */
	@Override
	public Class<?> dataType(Class<?> ... inputTypes) {
		if ((inputTypes.length == 2) && DataTypeUtils.allEqual(inputTypes, Boolean.class)) {
			return Boolean.class;
		} else {
			return null;
		}
	}
}