/*
 * @(#)$Id: ResidualCalculator.java,v 1.12 2001/10/18 23:52:19 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.verifier.regexp;

import com.sun.msv.grammar.*;

/**
 * computes regular expression derivative.
 * 
 * this class receives a regexp and computes the right language after eating
 * given token.
 * 
 * @author <a href="mailto:kohsuke.kawaguchi@eng.sun.com">Kohsuke KAWAGUCHI</a>
 */
public class ResidualCalculator implements ExpressionVisitorExpression {
	protected Token token;
	protected final ExpressionPool pool;
	
	public ResidualCalculator( ExpressionPool pool )	{ this.pool=pool; }
	
	/** compute the residual */
	final Expression calcResidual( Expression exp, ElementToken token ) {
		if( token.acceptedPatterns!=null && token.acceptedPatterns.length==1 ) {
			// we can use optimization table
			OptimizationTag ot;
			if(exp.verifierTag==null)
				exp.verifierTag = ot = new OptimizationTag();
			else {
				ot = (OptimizationTag)exp.verifierTag;
				Expression residual = (Expression)ot.simpleElementTokenResidual.get(token.acceptedPatterns[0]);
				if(residual!=null)
					return residual;	// cache hit.
			}
			
			this.token = token;
			Expression residual = exp.visit(this);
			// cache this residual
			ot.simpleElementTokenResidual.put(token.acceptedPatterns[0],residual);
			return residual;
		}
		
		// no chance of using cache.
		this.token = token;
		return exp.visit(this);
	}
	
	/** compute the residual */
	public final Expression calcResidual( Expression exp, Token token ) {
		if( token instanceof ElementToken )
			return calcResidual(exp,(ElementToken)token);
		
		this.token=token;
		return exp.visit(this);
	}
	
	public Expression onAttribute( AttributeExp exp ) {
		if(token.match(exp))	return Expression.epsilon;
		else				return Expression.nullSet;
	}
	public Expression onChoice( ChoiceExp exp ) {
		return pool.createChoice( exp.exp1.visit(this), exp.exp2.visit(this) );
	}
	public Expression onElement( ElementExp exp ) {
		if(token.match(exp))	return Expression.epsilon;
		else				return Expression.nullSet;
	}
	public Expression onOneOrMore( OneOrMoreExp exp ) {
		return pool.createSequence(
			exp.exp.visit(this),
			pool.createZeroOrMore(exp.exp) );
	}
	public Expression onMixed( MixedExp exp ) {
		// if token can be interpreted as anyString, eat it.
		if( token.matchAnyString() )	return exp;
		
		// otherwise, it must be consumed by the children.
		return pool.createMixed( exp.exp.visit(this) );
	}
	public Expression onEpsilon() {
		return Expression.nullSet;
	}
	public Expression onNullSet() {
		return Expression.nullSet;
	}
	public Expression onAnyString() {
		// anyString is not reduced to epsilon.
		// it remains there even after consuming StringToken.
		if(token.matchAnyString())		return Expression.anyString;
		else							return Expression.nullSet;
	}
	public Expression onRef( ReferenceExp exp ) {
		return exp.exp.visit(this);
	}
	public Expression onOther( OtherExp exp ) {
		return exp.exp.visit(this);
	}
	public Expression onSequence( SequenceExp exp ) {
		Expression r = pool.createSequence( exp.exp1.visit(this), exp.exp2 );
		
		if( exp.exp1.isEpsilonReducible() )
			return pool.createChoice( r, exp.exp2.visit(this) );
		else
			return r;
	}
	
	public Expression onData( DataExp exp ) {
		if(token.match(exp))	return Expression.epsilon;
		else					return Expression.nullSet;
	}
	
	public Expression onValue( ValueExp exp ) {
		if(token.match(exp))	return Expression.epsilon;
		else					return Expression.nullSet;
	}
	
	public Expression onList( ListExp exp ) {
		if(token.match(exp))	return Expression.epsilon;
		else					return Expression.nullSet;
	}
	
	public Expression onConcur( ConcurExp exp ) {
		return pool.createConcur(
			exp.exp1.visit(this), exp.exp2.visit(this) );
	}
	public Expression onInterleave( InterleaveExp exp ) {
		return pool.createChoice(
			pool.createInterleave( exp.exp1.visit(this), exp.exp2 ),
			pool.createInterleave( exp.exp1, exp.exp2.visit(this) ) );
	}
}