/*
 * Visitor.java January 2010
 *
 * Copyright (C) 2010, Niall Gallagher <niallg@users.sf.net>
 *
 * Licensed 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.
 */

package org.simpleframework.xml.strategy;

import org.simpleframework.xml.stream.InputNode;
import org.simpleframework.xml.stream.NodeMap;
import org.simpleframework.xml.stream.OutputNode;

/**
 * The <code>Visitor</code> interface represents an object that is 
 * used to visit each XML element during serialization. For the
 * deserialization process each XML element is visited before 
 * control is returned to the serializer. This allows a visitor
 * implementation to perform some operation based on the node 
 * that is being deserialized. Typically a visitor is used to
 * edit the node, for example it may remove or insert attributes.
 * <p>
 * In effect this can act much like a transformer that sits
 * between a <code>Strategy</code> implementation and the core
 * serializer. It enables interception and manipulation of the
 * node so that the resulting XML document can be customized in 
 * a way that can not be performed by the underlying strategy.
 * 
 * @author Niall Gallagher
 * 
 * @see org.simpleframework.xml.strategy.VisitorStrategy
 */
public interface Visitor {
   
   /**
    * This is used to intercept an XML element before it is read
    * by the underlying <code>Strategy</code> implementation. When
    * a node is intercepted it can be manipulated in such a way
    * that its semantics change. For example, this could be used 
    * to change the way a "class" attribute is represented, which
    * would allow the XML to appear in a language neutral format.
    *
    * @param type this is the type that represents the element
    * @param node this is the XML element to be intercepted
    */
   public void read(Type type, NodeMap<InputNode> node) throws Exception;
   
   /**
    * This is used to intercept an XML element after it is written
    * by the underlying <code>Strategy</code> implementation. When
    * a node is intercepted it can be manipulated in such a way
    * that its semantics change. For example, this could be used 
    * to change the way a "class" attribute is represented, which
    * would allow the XML to appear in a language neutral format.
    *
    * @param type this is the type that represents the element
    * @param node this is the XML element to be intercepted
    */
   public void write(Type type, NodeMap<OutputNode> node) throws Exception;
}
