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    * 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.                                           *
   ****************************************************************/
  package org.apache.jsieve.util;
  
  import org.apache.jsieve.exception.SieveException;
  import org.apache.jsieve.parser.generated.ASTargument;
  import org.apache.jsieve.parser.generated.ASTarguments;
  import org.apache.jsieve.parser.generated.ASTblock;
  import org.apache.jsieve.parser.generated.ASTcommand;
  import org.apache.jsieve.parser.generated.ASTcommands;
  import org.apache.jsieve.parser.generated.ASTstart;
  import org.apache.jsieve.parser.generated.ASTstring;
  import org.apache.jsieve.parser.generated.ASTstring_list;
  import org.apache.jsieve.parser.generated.ASTtest;
  import org.apache.jsieve.parser.generated.ASTtest_list;
  import org.apache.jsieve.parser.generated.Node;
  import org.apache.jsieve.parser.generated.SieveParserVisitor;
  import org.apache.jsieve.parser.generated.SimpleNode;
  
  /**
   * Traverses nodes.
   * Once instance can be safely shared between threads.
   */
  public class NodeTraverser {
      
      /**
       * Traverses the tree structure rooted at the given node.
       * The nodes contained are reported to the handler.
       * @param root not null
       * @param handler not null
       * @throws SieveException when traversal fails
       * @throws HaltTraversalException when traversal is halted by handler
       */
      public void traverse(final NodeHandler handler, final Node root) throws SieveException {
          final TraversalWorker worker = new TraversalWorker(handler);
          handler.start();
          root.jjtAccept(worker, null);
          handler.end();
      }
      
      /**
       * Traverses the tree structure rooted at the given node.
       * The nodes contained are reported to the handler.
       * @param root not null
       * @param handler not null
       * @throws SieveException when traversal fails
       * @throws HaltTraversalException when traversal is halted by handler
       */
      public void traverse(final SieveHandler handler, final Node root) throws SieveException {
          traverse(new NodeToSieveAdapter(handler), root);
      }
    
  
      /**
       * <p>Traverses a nodal tree structure.
       * An inner worker:
       * </p>
       * <ul>
       * <li>Allows a more fluent public API</li>
       * <li>Isolated the monotheaded code</li>
       * </ul>
       */
      private static final class TraversalWorker implements SieveParserVisitor {
          
          private final NodeHandler handler;
          
          /**
           * Constructs a traversal worker.
           * @param handler not null
           */
          public TraversalWorker(final NodeHandler handler) {
              super();
              this.handler = handler;
          }
          
          public Object visit(SimpleNode node, Object data) throws SieveException {
              handler.start(node);
              node.childrenAccept(this, null);
              handler.end(node);
              return null;
          }
      
          public Object visit(ASTstart node, Object data) throws SieveException {
             handler.start(node);
             node.childrenAccept(this, null);
             handler.end(node);
             return null;
         }
     
         public Object visit(ASTcommands node, Object data) throws SieveException {
             handler.start(node);
             node.childrenAccept(this, null);
             handler.end(node);
             return null;
         }
     
         public Object visit(ASTcommand node, Object data) throws SieveException {
             handler.start(node);
             node.childrenAccept(this, null);
             handler.end(node);
             return null;
         }
     
         public Object visit(ASTblock node, Object data) throws SieveException {
             handler.start(node);
             node.childrenAccept(this, null);
             handler.end(node);
             return null;
         }
     
         public Object visit(ASTarguments node, Object data) throws SieveException {
             handler.start(node);
             node.childrenAccept(this, null);
             handler.end(node);
             return null;
         }
     
         public Object visit(ASTargument node, Object data) throws SieveException {
             handler.start(node);
             node.childrenAccept(this, null);
             handler.end(node);
             return null;
         }
     
         public Object visit(ASTtest node, Object data) throws SieveException {
             handler.start(node);
             node.childrenAccept(this, null);
             handler.end(node);
             return null;
         }
     
         public Object visit(ASTtest_list node, Object data) throws SieveException {
             handler.start(node);
             node.childrenAccept(this, null);
             handler.end(node);
             return null;
         }
     
         public Object visit(ASTstring node, Object data) throws SieveException {
             handler.start(node);
             node.childrenAccept(this, null);
             handler.end(node);
             return null;
         }
     
         public Object visit(ASTstring_list node, Object data) throws SieveException {
             handler.start(node);
             node.childrenAccept(this, null);
             handler.end(node);
             return null;
         }
     }
 }