/*
 * 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.math;

import org.epochx.epox.Node;
import org.epochx.tools.util.*;

/**
 * A function node which performs the mathematical function of subtract.
 * 
 * Subtraction can be performed on inputs of the following types:
 * <ul>
 * <li>Integer</li>
 * <li>Long</li>
 * <li>Float</li>
 * <li>Double</li>
 * </ul>
 * 
 * Subtraction can be performed between mixed types, with a widening operation
 * performed and the result being of the wider of the two types.
 */
public class SubtractFunction extends Node {

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

	/**
	 * Constructs an SubtractFunction with two numerical child nodes. When
	 * evaluated, both children will be evaluated with the first subtracted from
	 * the second.
	 * 
	 * @param child1 The first child node.
	 * @param child2 The second child node.
	 */
	public SubtractFunction(final Node child1, final Node child2) {
		super(child1, child2);
	}

	/**
	 * Evaluates this function. Both child nodes are evaluated, the result of
	 * both must be of numeric type. If necessary, the inputs are widened to
	 * both be of the same type, then subtraction is performed and the return
	 * value will be of that wider type.
	 */
	@Override
	public Object evaluate() {
		final Object c1 = getChild(0).evaluate();
		final Object c2 = getChild(1).evaluate();

		final Class<?> returnType = TypeUtils.getNumericType(c1.getClass(), c2.getClass());

		if (returnType == Double.class) {
			// Subtract as doubles.
			final double d1 = NumericUtils.asDouble(c1);
			final double d2 = NumericUtils.asDouble(c2);

			return d1 - d2;
		} else if (returnType == Float.class) {
			// Subtract as floats.
			final float f1 = NumericUtils.asFloat(c1);
			final float f2 = NumericUtils.asFloat(c2);

			return f1 - f2;
		} else if (returnType == Long.class) {
			// Subtract as longs.
			final long l1 = NumericUtils.asLong(c1);
			final long l2 = NumericUtils.asLong(c2);

			return l1 - l2;
		} else if (returnType == Integer.class) {
			// Subtract as integers.
			final int i1 = NumericUtils.asInteger(c1);
			final int i2 = NumericUtils.asInteger(c2);

			return i1 - i2;
		}

		return null;
	}

	/**
	 * Returns the identifier of this function which is SUB.
	 */
	@Override
	public String getIdentifier() {
		return "SUB";
	}

	/**
	 * Returns this function node's return type for the given child input types.
	 * If there are two input types of numeric type then the return type will
	 * be the wider of those numeric types. In all other cases this method will
	 * return <code>null</code> to indicate that the inputs are invalid.
	 * 
	 * @return A numeric class or null if the input type is invalid.
	 */
	@Override
	public Class<?> getReturnType(final Class<?> ... inputTypes) {
		if (inputTypes.length == 2) {
			return TypeUtils.getNumericType(inputTypes);
		}
		return null;
	}
}
