001/*
002 *  Licensed to the Apache Software Foundation (ASF) under one
003 *  or more contributor license agreements.  See the NOTICE file
004 *  distributed with this work for additional information
005 *  regarding copyright ownership.  The ASF licenses this file
006 *  to you under the Apache License, Version 2.0 (the
007 *  "License"); you may not use this file except in compliance
008 *  with the License.  You may obtain a copy of the License at
009 *  
010 *    http://www.apache.org/licenses/LICENSE-2.0
011 *  
012 *  Unless required by applicable law or agreed to in writing,
013 *  software distributed under the License is distributed on an
014 *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015 *  KIND, either express or implied.  See the License for the
016 *  specific language governing permissions and limitations
017 *  under the License. 
018 *  
019 */
020package org.apache.directory.api.ldap.model.filter;
021
022
023import java.util.List;
024
025
026/**
027 * Filter expression tree node visitor interface. Note that this is a variation
028 * of the extrinsic visitor variation. It has the following advantages over the
029 * standard visitor pattern:
030 * <ul>
031 *   <li>Visitor takes responsibility that a visitor can visit a node</li>
032 *   <li>Each visitor knows which types of concrete classes it can visit</li>
033 *   <li>New visitors can be created without changing the node class</li>
034 *   <li>New node classes can be added without having to change old visitors</li>
035 *   <li>Visitation order can be controled in every respect:</li>
036 *   <li>
037 *     <ul>
038 *       <li>Visitation rejection with canVisit() and/or getOrder()</li>
039 *       <li>Recursive visitation ordering with isPrefix()</li>
040 *       <li>Child visitation ordering with getOrder()</li>
041 *     </ul>
042 *   </li>
043 * </ul>
044 * 
045 * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
046 */
047public interface FilterVisitor
048{
049    /**
050     * Visits a filter expression AST using a specific visitation order.
051     * 
052     * @param node the node to visit
053     * @return node the resulting modified node
054     */
055    Object visit( ExprNode node );
056
057
058    /**
059     * Checks to see if a node can be visited.
060     * 
061     * @param node the node to be visited
062     * @return whether or node the node should be visited
063     */
064    boolean canVisit( ExprNode node );
065
066
067    /**
068     * Determines whether the visitation order is prefix or postfix.
069     * 
070     * @return true if the visitation is in prefix order, false otherwise.
071     */
072    boolean isPrefix();
073
074
075    /**
076     * Get the array of children to visit sequentially to determine the order of
077     * child visitations. Some children may not be returned at all if canVisit()
078     * returns false on them.
079     * 
080     * @param node the parent branch node
081     * @param children the child node array
082     * @return the new reordered array of children
083     */
084    List<ExprNode> getOrder( BranchNode node, List<ExprNode> children );
085}