/*
 * @(#)$Id: LabelRefState.java,v 1.5 2001/05/01 18:13:07 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.reader.relax;

import com.sun.msv.grammar.Expression;
import com.sun.msv.grammar.ReferenceExp;
import com.sun.msv.grammar.relax.RELAXModule;
import com.sun.msv.reader.ExpressionWithoutChildState;
import com.sun.msv.reader.GrammarReader;

/**
 * base implementation of HedgeRefState and ElementRefState.
 * 
 * this class resolves namespace attribute and label attribute into the actual
 * ReferenceExp object.
 * 
 * @author <a href="mailto:kohsuke.kawaguchi@eng.sun.com">Kohsuke KAWAGUCHI</a>
 */
abstract class LabelRefState extends ExpressionWithoutChildState
{
	protected Expression makeExpression()
	{
		final String label = startTag.getAttribute("label");
		final String namespace = startTag.getAttribute("namespace");
		final RELAXReader reader = (RELAXReader)this.reader;
		
		if(label==null)
		{// label attribute is required.
			reader.reportError( GrammarReader.ERR_MISSING_ATTRIBUTE,
				startTag.localName,"label");
			// recover by returning something that can be interpreted as Pattern
			return Expression.nullSet;
		}
		
		return resolve(namespace,label);
	}
	
	/** gets or creates appropriate reference */
	protected abstract Expression resolve( String namespace, String label );
}