/*
 * 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;

/**
 * The <code>VariableNode</code> class provides a wrapper for <code>Variable</code>
 * objects. Each <code>Node</code> must only appear in one place in a tree, so to
 * allow the same variable instance to be reused in multiple places, variables
 * are not themselves nodes. Instead, a <code>VariableNode</code> wrapper is used. This
 * allows the same variable object to be used in multiple locations within the same 
 * program tree while keeping the nodes unique.
 * 
 * @see Variable
 * 
 * @since 2.0
 */
public class VariableNode extends Node {

	private Variable variable;

	/**
	 * Constructs a new <code>VariableNode</code> wrapper for the given variable
	 * 
	 * @param variable the <code>Variable</code> object to wrap
	 */
	public VariableNode(Variable variable) {
		if (variable == null) {
			throw new IllegalArgumentException("variable cannot be null");
		}
		
		this.variable = variable;
	}

	/**
	 * Returns the <code>Variable</code> object that this node is a wrapper for
	 * 
	 * @return the variable
	 */
	public Variable getVariable() {
		return variable;
	}

	/**
	 * Returns the value of the variable
	 * 
	 * @return the variable's value
	 */
	@Override
	public Object evaluate() {
		return variable.getValue();
	}

	/**
	 * Returns the name of the variable
	 * 
	 * @return the name of the variable
	 */
	@Override
	public String getIdentifier() {
		return variable.getName();
	}

	/**
	 * Returns the data-type of the variable
	 * 
	 * @return the data-type of the variable's value
	 */
	@Override
	public Class<?> dataType(Class<?> ... inputTypes) {
		if (inputTypes.length != 0) {
			throw new IllegalArgumentException("variables do not have input types");
		}

		return variable.getDataType();
	}

	/**
	 * Returns a string representation of the variable
	 * 
	 * @return a string representation of the variable
	 */
	@Override
	public String toString() {
		return variable.getName();
	}

	/**
	 * Compares this <code>VariableNode</code> to the given object for equality. Two
	 * <code>VariableNode</code> objects are only considered to be equal if they
	 * refer to the same variable instance.
	 * 
	 * @return <code>true</code> if the given object refers to the same variable
	 *         instance as this node and <code>false</code> otherwise
	 */
	@Override
	public boolean equals(Object obj) {
		return (obj instanceof VariableNode) && (((VariableNode) obj).variable == this.variable);
	}
}