code: /*
   * 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.axes;
  
  import org.apache.xml.dtm.DTM;
  import org.apache.xml.dtm.DTMAxisIterator;
  import org.apache.xpath.XPathContext;
  
  /**
   * Walker for a reverse axes.
   * @see <a href="http://www.w3.org/TR/xpath#predicates">XPath 2.4 Predicates</a>
   */
  public class ReverseAxesWalker extends AxesWalker
  {
      static final long serialVersionUID = 2847007647832768941L;
  
    /**
     * Construct an AxesWalker using a LocPathIterator.
     *
     * @param locPathIterator The location path iterator that 'owns' this walker.
     */
    ReverseAxesWalker(LocPathIterator locPathIterator, int axis)
    {
      super(locPathIterator, axis);
    }
    
    /**
     * Set the root node of the TreeWalker.
     * (Not part of the DOM2 TreeWalker interface).
     *
     * @param root The context node of this step.
     */
    public void setRoot(int root)
    {
      super.setRoot(root);
      m_iterator = getDTM(root).getAxisIterator(m_axis);
      m_iterator.setStartNode(root);
    }
  
    /**
     * Detaches the walker from the set which it iterated over, releasing
     * any computational resources and placing the iterator in the INVALID
     * state.
     */
    public void detach()
    {
      m_iterator = null;
      super.detach();
    }
    
    /**
     * Get the next node in document order on the axes.
     *
     * @return the next node in document order on the axes, or null.
     */
    protected int getNextNode()
    {
      if (m_foundLast)
        return DTM.NULL;
  
      int next = m_iterator.next();
      
      if (m_isFresh)
        m_isFresh = false;
  
      if (DTM.NULL == next)
        this.m_foundLast = true;
  
      return next;
    }
  
  
    /**
     * Tells if this is a reverse axes.  Overrides AxesWalker#isReverseAxes.
     *
     * @return true for this class.
     */
    public boolean isReverseAxes()
    {
      return true;
    }
  
  //  /**
  //   *  Set the root node of the TreeWalker.
  //   *
  //   * @param root The context node of this step.
  //   */
  //  public void setRoot(int root)
  //  {
  //    super.setRoot(root);
  //  }
  
    /**
     * Get the current sub-context position.  In order to do the
     * reverse axes count, for the moment this re-searches the axes
     * up to the predicate.  An optimization on this is to cache
     * the nodes searched, but, for the moment, this case is probably
     * rare enough that the added complexity isn't worth it.
     *
     * @param predicateIndex The predicate index of the proximity position.
     *
     * @return The pridicate index, or -1.
     */
    protected int getProximityPosition(int predicateIndex)
    {
      // A negative predicate index seems to occur with
      // (preceding-sibling::*|following-sibling::*)/ancestor::*[position()]/*[position()]
      // -sb
      if(predicateIndex < 0)
        return -1;
        
      int count = m_proximityPositions[predicateIndex];
        
      if (count <= 0)
      {
        AxesWalker savedWalker = wi().getLastUsedWalker();
  
        try
        {
          ReverseAxesWalker clone = (ReverseAxesWalker) this.clone();
  
          clone.setRoot(this.getRoot());
  
          clone.setPredicateCount(predicateIndex);
  
          clone.setPrevWalker(null);
          clone.setNextWalker(null);
          wi().setLastUsedWalker(clone);
  
          // Count 'em all
          count++;
          int next;
  
          while (DTM.NULL != (next = clone.nextNode()))
          {
            count++;
          }
  
          m_proximityPositions[predicateIndex] = count;
        }
        catch (CloneNotSupportedException cnse)
        {
  
          // can't happen
        }
        finally
        {
          wi().setLastUsedWalker(savedWalker);
        }
      }
      
      return count;
    }
  
    /**
     * Count backwards one proximity position.
     *
     * @param i The predicate index.
     */
    protected void countProximityPosition(int i)
    {
      if (i < m_proximityPositions.length)
        m_proximityPositions[i]--;
    }
  
    /**
     * Get the number of nodes in this node list.  The function is probably ill
     * named?
     *
     *
     * @param xctxt The XPath runtime context.
     *
     * @return the number of nodes in this node list.
     */
    public int getLastPos(XPathContext xctxt)
    {
  
      int count = 0;
      AxesWalker savedWalker = wi().getLastUsedWalker();
  
      try
      {
        ReverseAxesWalker clone = (ReverseAxesWalker) this.clone();
  
        clone.setRoot(this.getRoot());
  
        clone.setPredicateCount(m_predicateIndex);
  
        clone.setPrevWalker(null);
        clone.setNextWalker(null);
        wi().setLastUsedWalker(clone);
  
        // Count 'em all
        // count = 1;
        int next;
  
        while (DTM.NULL != (next = clone.nextNode()))
        {
          count++;
        }
      }
      catch (CloneNotSupportedException cnse)
      {
  
        // can't happen
      }
      finally
      {
        wi().setLastUsedWalker(savedWalker);
      }
  
      return count;
    }
    
    /**
     * Returns true if all the nodes in the iteration well be returned in document 
     * order.
     * Warning: This can only be called after setRoot has been called!
     * 
     * @return false.
     */
    public boolean isDocOrdered()
    {
      return false;  // I think.
    }
    
    /** The DTM inner traversal class, that corresponds to the super axis. */
    protected DTMAxisIterator m_iterator;
  }
  