/*
 * @(#)$Id: GrammarState.java,v 1.11 2001/10/12 01:37:30 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.trex;

import com.sun.msv.util.StartTagInfo;
import com.sun.msv.reader.State;
import com.sun.msv.grammar.Expression;
import com.sun.msv.grammar.trex.TREXGrammar;

/**
 * parses <grammar> element.
 * 
 * this state is used to parse top-level grammars and nested grammars.
 * grammars merged by include element are handled by MergeGrammarState.
 * 
 * <p>
 * this class provides a new TREXGrammar object to localize names defined
 * within this grammar.
 * 
 * @author <a href="mailto:kohsuke.kawaguchi@eng.sun.com">Kohsuke KAWAGUCHI</a>
 */
public class GrammarState extends DivInGrammarState {
	protected TREXGrammar previousGrammar;
	protected TREXGrammar newGrammar;
	
	protected Expression makeExpression() {
		// start pattern is the grammar-as-a-pattern.
		return newGrammar;
	}

	protected void startSelf() {
		super.startSelf();
		
		previousGrammar = getReader().grammar;
		newGrammar = getReader().sfactory.createGrammar( reader.pool, previousGrammar );
		getReader().grammar = newGrammar;
	}

	public void endSelf() {
		final TREXGrammar grammar = getReader().grammar;
		
		// detect references to undefined pattterns
		reader.detectUndefinedOnes(
			grammar.namedPatterns, TREXBaseReader.ERR_UNDEFINED_PATTERN );

		// is start pattern defined?
		if( grammar.exp==null ) {
			reader.reportError( reader.ERR_MISSING_TOPLEVEL );
			grammar.exp = Expression.nullSet;	// recover by assuming a valid pattern
		}
		
		// this method is called when this State is about to be removed.
		// restore the previous grammar
		if( previousGrammar!=null )
			getReader().grammar = previousGrammar;
		
		// if the previous grammar is null, it means this grammar is the top-level
		// grammar. In that case, leave it there so that GrammarReader can access
		// the loaded grammar.
			
		super.endSelf();
	}
}