/*
 * 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: VariableSafeAbsRef.java 468655 2006-10-28 07:12:06Z minchau $
 */
package org.apache.xpath.operations;

import org.apache.xml.dtm.DTMManager;
import org.apache.xpath.Expression;
import org.apache.xpath.XPathContext;
import org.apache.xpath.objects.XNodeSet;
import org.apache.xpath.objects.XObject;


This is a "smart" variable reference that is used in situations where 
an absolute path is optimized into a variable reference, but may 
be used in some situations where the document context may have changed.
For instance, in select="document(doc/@href)//name[//salary > 7250]", the 
root in the predicate will be different for each node in the set.  While 
this is easy to detect statically in this case, in other cases static 
detection would be very hard or impossible.  So, this class does a dynamic check 
to make sure the document context of the referenced variable is the same as 
the current document context, and, if it is not, execute the referenced variable's 
expression with the current context instead.
/**
 * This is a "smart" variable reference that is used in situations where 
 * an absolute path is optimized into a variable reference, but may 
 * be used in some situations where the document context may have changed.
 * For instance, in select="document(doc/@href)//name[//salary > 7250]", the 
 * root in the predicate will be different for each node in the set.  While 
 * this is easy to detect statically in this case, in other cases static 
 * detection would be very hard or impossible.  So, this class does a dynamic check 
 * to make sure the document context of the referenced variable is the same as 
 * the current document context, and, if it is not, execute the referenced variable's 
 * expression with the current context instead.
 */
public class VariableSafeAbsRef extends Variable
{
    static final long serialVersionUID = -9174661990819967452L;
	
  
Dereference the variable, and return the reference value.  Note that lazy 
evaluation will occur.  If a variable within scope is not found, a warning 
will be sent to the error listener, and an empty nodeset will be returned.
Params:
xctxt – The runtime execution context.
Throws:
TransformerException – 
Returns:
The evaluated variable, or an empty nodeset if not found./**
   * Dereference the variable, and return the reference value.  Note that lazy 
   * evaluation will occur.  If a variable within scope is not found, a warning 
   * will be sent to the error listener, and an empty nodeset will be returned.
   *
   *
   * @param xctxt The runtime execution context.
   *
   * @return The evaluated variable, or an empty nodeset if not found.
   *
   * @throws javax.xml.transform.TransformerException
   */
  public XObject execute(XPathContext xctxt, boolean destructiveOK) 
  	throws javax.xml.transform.TransformerException
  {
  	XNodeSet xns = (XNodeSet)super.execute(xctxt, destructiveOK);
  	DTMManager dtmMgr = xctxt.getDTMManager();
  	int context = xctxt.getContextNode();
  	if(dtmMgr.getDTM(xns.getRoot()).getDocument() != 
  	   dtmMgr.getDTM(context).getDocument())
  	{
  		Expression expr = (Expression)xns.getContainedIter();
  		xns = (XNodeSet)expr.asIterator(xctxt, context);
  	}
  	return xns;
  }

}