/*
 * @(#)$Id: NameClassCollisionChecker.java,v 1.1 2001/10/11 19:25:31 Bear Exp $
 *
 * Copyright 2001 Sun Microsystems, Inc. All Rights Reserved.
 * 
 * This software is the proprietary information of Sun Microsystems, Inc.  
 * Use is subject to license terms.
 * 
 */
package com.sun.msv.grammar.util;

import com.sun.msv.grammar.*;

/**
 * Computes if two name classes collide or not.
 * 
 * <p>
 * To be more precise, this class works as a function that takes two name classes
 * and computes if the intersection of them is empty or not.
 * 
 * <p>
 * To compute, create an instance and call the check method. This class is not
 * reentrant, so the caller is responsible not to reuse the same object by multiple
 * threads.
 * 
 * <p>
 * The same thing can be computed by using the {@link NameClass#intersection} method,
 * but generally this method is faster.
 * 
 * @author <a href="mailto:kohsuke.kawaguchi@sun.com">Kohsuke KAWAGUCHI</a>
 */
public class NameClassCollisionChecker implements NameClassVisitor {
			
	/** Two name classes to be tested. */
	NameClass nc1,nc2;
			
	/**
	 * This exception will be thrown when a collision is found.
	 */
	private final RuntimeException eureka = new RuntimeException();
			
	/**
	 * Returns true if two name classes collide.
	 */
	public boolean check( NameClass _new, NameClass _old ) {
				
		if( _new instanceof SimpleNameClass ) {
			// short cut for 90% of the cases
			SimpleNameClass nnc = (SimpleNameClass)_new;
			return _old.accepts( nnc.namespaceURI, nnc.localName );
		}
				
		try {
			nc1 = _new;
			nc2 = _old;
			_old.visit(this);
			_new.visit(this);
			return false;
		} catch( RuntimeException e ) {
			if(e==eureka)	return true;	// the collision was found.
			throw e;
		}
	}
			
	private void probe( String uri, String local ) {
		if(nc1.accepts(uri,local) && nc2.accepts(uri,local))
			// conflict is found.
			throw eureka;
	}
			
	private /*static*/ final String MAGIC = "\u0000";
			
	public Object onAnyName( AnyNameClass nc ) {
		probe(MAGIC,MAGIC);
		return null;
	}
	public Object onNsName( NamespaceNameClass nc ) {
		probe(nc.namespaceURI,MAGIC);
		return null;
	}
	public Object onSimple( SimpleNameClass nc ) {
		probe(nc.namespaceURI,nc.localName);
		return null;
	}
	public Object onNot( NotNameClass nc ) {
		nc.child.visit(this);
		return null;
	}
	public Object onDifference( DifferenceNameClass nc ) {
		nc.nc1.visit(this);
		nc.nc2.visit(this);
		return null;
	}
	public Object onChoice( ChoiceNameClass nc ) {
		nc.nc1.visit(this);
		nc.nc2.visit(this);
		return null;
	}
}