/*
 * 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;

import org.apache.commons.lang.ObjectUtils;

/**
 * Literal values are terminal nodes with a specific value. Typically the value of a
 * literal will not change.
 * 
 * @see Variable
 * 
 * @since 2.0
 */
public class Literal extends Node {

	private Object value;

	/**
	 * Constructs a new <code>Literal</code> node with the given value. Evaluation
	 * of this literal will return the value set here. The data-type of this
	 * node will be determined by the type of the object specified here.
	 * 
	 * @param value the value of this literal
	 */
	public Literal(Object value) {
		this.value = value;
	}

	/**
	 * Returns the value of this literal. Has the same functionality as calling
	 * <code>getValue</code>.
	 * 
	 * @return the value of this literal
	 */
	@Override
	public Object evaluate() {
		return value;
	}

	/**
	 * Returns this node's string representation, which is the string
	 * representation of the literal value
	 * 
	 * @return a <code>String</code> representation
	 */
	@Override
	public String getIdentifier() {
		return toString();
	}

	/**
	 * Returns the data-type of this node. The data-type of a literal node
	 * is the data-type of its value. If no value has been set then
	 * <code>null</code> will be returned.
	 * 
	 * @param inputTypes the data-types of the node's inputs. Literals
	 *        take no inputs so this should be an empty array.
	 * @return the data-type of this node
	 * @throws IllegalArgumentException if <code>inputTypes</code> is
	 *         anything other than an empty array
	 */
	@Override
	public Class<?> dataType(Class<?> ... inputTypes) {
		if (inputTypes.length != 0) {
			throw new IllegalArgumentException("literals have no input types");
		}

		if (value != null) {
			return value.getClass();
		} else {
			return null;
		}
	}

	/**
	 * Sets the value of this literal. Implementations of this class may
	 * wish to use this method to delay the setting of a literal's value.
	 * 
	 * @param value the value to set for this literal
	 */
	protected void setValue(Object value) {
		this.value = value;
	}

	/**
	 * Returns the current value of this literal
	 * 
	 * @return the value of this literal
	 */
	public Object getValue() {
		return value;
	}

	/**
	 * Returns this node's string representation, which is the string
	 * representation of the literal value. If no value is set then an empty
	 * string will be returned.
	 * 
	 * @return a <code>String</code> representation.
	 */
	@Override
	public String toString() {
		if (value != null) {
			return value.toString();
		} else {
			return "";
		}
	}

	/**
	 * Compares this literal to the given object for equality. An object is equal to this literal 
	 * if it is an instance of <code>Literal</code> and its value is equal to this literal's value.
	 * 
	 * @return <code>true</code> if the two objects are equal, <code>false</code> otherwise.
	 */
	@Override
	public boolean equals(Object obj) {
		if (!(obj instanceof Literal)) {
			return false;
		}

		Object objVal = ((Literal) obj).value;
		Object thisVal = value;

		return ObjectUtils.equals(objVal, thisVal);
	}

	/**
	 * Creates a new <code>Literal</code> instance which is a copy of this instance.
	 * The clone will contain a value which is a reference to the same object as
	 * this literal's value. For mutable object values, users should consider
	 * extending this class to provide a clone method which can provide an
	 * appropriate deep clone.
	 * 
	 * @return a new <code>Literal</code> instance which is a clone of this object
	 */
	@Override
	public Literal clone() {
		Literal clone = (Literal) super.clone();

		clone.value = value;

		return clone;
	}

	/**
	 * Constructs a new instance of this literal. This implementation is 
	 * equivalent to calling <code>clone()</code>.
	 * 
	 * @return a new <code>Literal</code> instance which is a clone of this object
	 */
	@Override
	public Literal newInstance() {
		return clone();
	}
}