/*
 *  JFLAP - Formal Languages and Automata Package
 * 
 * 
 *  Susan H. Rodger
 *  Computer Science Department
 *  Duke University
 *  August 27, 2009

 *  Copyright (c) 2002-2009
 *  All rights reserved.

 *  JFLAP is open source software. Please see the LICENSE for terms.
 *
 */





package grammar;

import java.util.Comparator;

/**
 * This is a comparator for productions that sorts productions lexigraphically,
 * with the exception that the start variable is always ordered first on the
 * LHS.
 * 
 * @author Thomas Finley
 */

public class ProductionComparator implements Comparator {
	/**
	 * Instantiates a comparator, getting the start variable from a given
	 * grammar.
	 * 
	 * @param grammar
	 *            the grammar
	 * @throws IllegalArgumentException
	 *             if the grammar does not have a start variable
	 */
	public ProductionComparator(Grammar grammar) {
		this(grammar.getStartVariable());
	}

	/**
	 * Instantiates a comparator, with the start variable is passed in
	 * explicitly.
	 * 
	 * @param variable
	 *            the start variable
	 */
	public ProductionComparator(String variable) {
		start = variable;
		if (start == null)
			throw new IllegalArgumentException("Null start variable!");
	}

	/**
	 * Compares two productions.
	 */
	public int compare(Object o1, Object o2) {
		Production p1 = (Production) o1, p2 = (Production) o2;
		if (start.equals(p1.getLHS())) {
			if (p1.getLHS().equals(p2.getLHS()))
				return 0;
			else
				return -1;
		}
		if (start.equals(p2.getLHS()))
			return 1;
		return p1.getLHS().compareTo(p2.getRHS());
	}

	/**
	 * Returns the start variable this comparator keys on.
	 * 
	 * @return the start variable
	 */
	public String getStartVariable() {
		return start;
	}

	/**
	 * Included to ensure compatibility with equals.
	 * 
	 * @return a hash code for this object
	 */
	public int hashCode() {
		return getClass().hashCode() ^ start.hashCode();
	}

	/**
	 * Two production comparators are equal if they have the same start
	 * variable.
	 * 
	 * @param object
	 *            the object to test for equality
	 * @return if the two objects are equal
	 */
	public boolean equals(Object object) {
		try {
			ProductionComparator c = (ProductionComparator) object;
			return c.start.equals(start);
		} catch (ClassCastException e) {
			return false;
		}
	}

	/** The start variable. */
	private String start = null;
}