/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the  "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
/*
 * $Id$
 */
package org.apache.xpath;

import org.apache.xpath.axes.LocPathIterator;
import org.apache.xpath.axes.UnionPathIterator;
import org.apache.xpath.functions.Function;
import org.apache.xpath.objects.XNumber;
import org.apache.xpath.objects.XString;
import org.apache.xpath.operations.Operation;
import org.apache.xpath.operations.UnaryOperation;
import org.apache.xpath.operations.Variable;
import org.apache.xpath.patterns.NodeTest;
import org.apache.xpath.patterns.StepPattern;
import org.apache.xpath.patterns.UnionPattern;

/**
 * A derivation from this class can be passed to a class that implements 
 * the XPathVisitable interface, to have the appropriate method called 
 * for each component of the XPath.  Aside from possible other uses, the 
 * main intention is to provide a reasonable means to perform expression 
 * rewriting.
 * 
 * <p>Each method has the form 
 * <code>boolean visitComponentType(ExpressionOwner owner, ComponentType compType)</code>. 
 * The ExpressionOwner argument is the owner of the component, and can 
 * be used to reset the expression for rewriting.  If a method returns 
 * false, the sub hierarchy will not be traversed.</p>
 * 
 * <p>This class is meant to be a base class that will be derived by concrete classes, 
 * and doesn't much except return true for each method.</p>
 */
public class XPathVisitor
{
	/**
	 * Visit a LocationPath.
	 * @param owner The owner of the expression, to which the expression can 
	 *              be reset if rewriting takes place.
	 * @param path The LocationPath object.
	 * @return true if the sub expressions should be traversed.
	 */
	public boolean visitLocationPath(ExpressionOwner owner, LocPathIterator path)
	{
		return true;
	}

	/**
	 * Visit a UnionPath.
	 * @param owner The owner of the expression, to which the expression can 
	 *              be reset if rewriting takes place.
	 * @param path The UnionPath object.
	 * @return true if the sub expressions should be traversed.
	 */
	public boolean visitUnionPath(ExpressionOwner owner, UnionPathIterator path)
	{
		return true;
	}
	
	/**
	 * Visit a step within a location path.
	 * @param owner The owner of the expression, to which the expression can 
	 *              be reset if rewriting takes place.
	 * @param step The Step object.
	 * @return true if the sub expressions should be traversed.
	 */
	public boolean visitStep(ExpressionOwner owner, NodeTest step)
	{
		return true;
	}
		
	/**
	 * Visit a predicate within a location path.  Note that there isn't a 
	 * proper unique component for predicates, and that the expression will 
	 * be called also for whatever type Expression is.
	 * 
	 * @param owner The owner of the expression, to which the expression can 
	 *              be reset if rewriting takes place.
	 * @param pred The predicate object.
	 * @return true if the sub expressions should be traversed.
	 */
	public boolean visitPredicate(ExpressionOwner owner, Expression pred)
	{
		return true;
	}

	/**
	 * Visit a binary operation.
	 * @param owner The owner of the expression, to which the expression can 
	 *              be reset if rewriting takes place.
	 * @param op The operation object.
	 * @return true if the sub expressions should be traversed.
	 */
	public boolean visitBinaryOperation(ExpressionOwner owner, Operation op)
	{
		return true;
	}

	/**
	 * Visit a unary operation.
	 * @param owner The owner of the expression, to which the expression can 
	 *              be reset if rewriting takes place.
	 * @param op The operation object.
	 * @return true if the sub expressions should be traversed.
	 */
	public boolean visitUnaryOperation(ExpressionOwner owner, UnaryOperation op)
	{
		return true;
	}
	
	/**
	 * Visit a variable reference.
	 * @param owner The owner of the expression, to which the expression can 
	 *              be reset if rewriting takes place.
	 * @param var The variable reference object.
	 * @return true if the sub expressions should be traversed.
	 */
	public boolean visitVariableRef(ExpressionOwner owner, Variable var)
	{
		return true;
	}

	/**
	 * Visit a function.
	 * @param owner The owner of the expression, to which the expression can 
	 *              be reset if rewriting takes place.
	 * @param func The function reference object.
	 * @return true if the sub expressions should be traversed.
	 */
	public boolean visitFunction(ExpressionOwner owner, Function func)
	{
		return true;
	}
	
	/**
	 * Visit a match pattern.
	 * @param owner The owner of the expression, to which the expression can 
	 *              be reset if rewriting takes place.
	 * @param pattern The match pattern object.
	 * @return true if the sub expressions should be traversed.
	 */
	public boolean visitMatchPattern(ExpressionOwner owner, StepPattern pattern)
	{
		return true;
	}
	
	/**
	 * Visit a union pattern.
	 * @param owner The owner of the expression, to which the expression can 
	 *              be reset if rewriting takes place.
	 * @param pattern The union pattern object.
	 * @return true if the sub expressions should be traversed.
	 */
	public boolean visitUnionPattern(ExpressionOwner owner, UnionPattern pattern)
	{
		return true;
	}
	
	/**
	 * Visit a string literal.
	 * @param owner The owner of the expression, to which the expression can 
	 *              be reset if rewriting takes place.
	 * @param str The string literal object.
	 * @return true if the sub expressions should be traversed.
	 */
	public boolean visitStringLiteral(ExpressionOwner owner, XString str)
	{
		return true;
	}


	/**
	 * Visit a number literal.
	 * @param owner The owner of the expression, to which the expression can 
	 *              be reset if rewriting takes place.
	 * @param num The number literal object.
	 * @return true if the sub expressions should be traversed.
	 */
	public boolean visitNumberLiteral(ExpressionOwner owner, XNumber num)
	{
		return true;
	}


}