/*
 * 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.Axis;
import org.apache.xml.dtm.DTM;
import org.apache.xml.dtm.DTMIterator;
import org.apache.xpath.Expression;
import org.apache.xpath.ExpressionOwner;
import org.apache.xpath.XPathContext;
import org.apache.xpath.XPathVisitor;
import org.apache.xpath.compiler.Compiler;
import org.apache.xpath.compiler.OpCodes;
import org.apache.xpath.objects.XNodeSet;

/**
 * Walker for the OP_VARIABLE, or OP_EXTFUNCTION, or OP_FUNCTION, or OP_GROUP,
 * op codes.
 * @see <a href="http://www.w3.org/TR/xpath#NT-FilterExpr">XPath FilterExpr descriptions</a>
 */
public class FilterExprWalker extends AxesWalker
{
    static final long serialVersionUID = 5457182471424488375L;

  /**
   * Construct a FilterExprWalker using a LocPathIterator.
   *
   * @param locPathIterator non-null reference to the parent iterator.
   */
  public FilterExprWalker(WalkingIterator locPathIterator)
  {
    super(locPathIterator, Axis.FILTEREDLIST);
  }

  /**
   * Init a FilterExprWalker.
   *
   * @param compiler non-null reference to the Compiler that is constructing.
   * @param opPos positive opcode position for this step.
   * @param stepType The type of step.
   *
   * @throws javax.xml.transform.TransformerException
   */
  public void init(Compiler compiler, int opPos, int stepType)
          throws javax.xml.transform.TransformerException
  {

    super.init(compiler, opPos, stepType);

    // Smooth over an anomily in the opcode map...
    switch (stepType)
    {
    case OpCodes.OP_FUNCTION :
    case OpCodes.OP_EXTFUNCTION :
    	m_mustHardReset = true;
    case OpCodes.OP_GROUP :
    case OpCodes.OP_VARIABLE :
      m_expr = compiler.compile(opPos);
      m_expr.exprSetParent(this);
      //if((OpCodes.OP_FUNCTION == stepType) && (m_expr instanceof org.apache.xalan.templates.FuncKey))
      if(m_expr instanceof org.apache.xpath.operations.Variable)
      {
      	// hack/temp workaround
      	m_canDetachNodeset = false;
      }
      break;
    default :
      m_expr = compiler.compile(opPos + 2);
      m_expr.exprSetParent(this);
    }
//    if(m_expr instanceof WalkingIterator)
//    {
//      WalkingIterator wi = (WalkingIterator)m_expr;
//      if(wi.getFirstWalker() instanceof FilterExprWalker)
//      {
//      	FilterExprWalker fw = (FilterExprWalker)wi.getFirstWalker();
//      	if(null == fw.getNextWalker())
//      	{
//      		m_expr = fw.m_expr;
//      		m_expr.exprSetParent(this);
//      	}
//      }
//      		
//    }
  }
  
  /**
   * 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()
  {  
  	super.detach();
  	if (m_canDetachNodeset)
  	{
  	  m_exprObj.detach();
  	}
  	m_exprObj = null;
  }

  /**
   *  Set the root node of the TreeWalker.
   *
   * @param root non-null reference to the root, or starting point of 
   *        the query.
   */
  public void setRoot(int root)
  {

    super.setRoot(root);

  	m_exprObj = FilterExprIteratorSimple.executeFilterExpr(root, 
  	                  m_lpi.getXPathContext(), m_lpi.getPrefixResolver(), 
  	                  m_lpi.getIsTopLevel(), m_lpi.m_stackFrame, m_expr);

  }

  /**
   * Get a cloned FilterExprWalker.
   *
   * @return A new FilterExprWalker that can be used without mutating this one.
   *
   * @throws CloneNotSupportedException
   */
  public Object clone() throws CloneNotSupportedException
  {

    FilterExprWalker clone = (FilterExprWalker) super.clone();

    if (null != m_exprObj)
      clone.m_exprObj = (XNodeSet) m_exprObj.clone();

    return clone;
  }
  
  /**
   * This method needs to override AxesWalker.acceptNode because FilterExprWalkers
   * don't need to, and shouldn't, do a node test.
   * @param n  The node to check to see if it passes the filter or not.
   * @return  a constant to determine whether the node is accepted,
   *   rejected, or skipped, as defined  above .
   */
  public short acceptNode(int n)
  {

    try
    {
      if (getPredicateCount() > 0)
      {
        countProximityPosition(0);

        if (!executePredicates(n, m_lpi.getXPathContext()))
          return DTMIterator.FILTER_SKIP;
      }

      return DTMIterator.FILTER_ACCEPT;
    }
    catch (javax.xml.transform.TransformerException se)
    {
      throw new RuntimeException(se.getMessage());
    }
  }

  /**
   *  Moves the <code>TreeWalker</code> to the next visible node in document
   * order relative to the current node, and returns the new node. If the
   * current node has no next node,  or if the search for nextNode attempts
   * to step upward from the TreeWalker's root node, returns
   * <code>null</code> , and retains the current node.
   * @return  The new node, or <code>null</code> if the current node has no
   *   next node  in the TreeWalker's logical view.
   */
  public int getNextNode()
  {

    if (null != m_exprObj)
    {
       int next = m_exprObj.nextNode();
       return next;
    }
    else
      return DTM.NULL;
  }
  
  /**
   * Get the index of the last node that can be itterated to.
   *
   *
   * @param xctxt XPath runtime context.
   *
   * @return the index of the last node that can be itterated to.
   */
  public int getLastPos(XPathContext xctxt)
  {
    return m_exprObj.getLength();
  }
  
  /** The contained expression. Should be non-null.
   *  @serial   */
  private Expression m_expr;

  /** The result of executing m_expr.  Needs to be deep cloned on clone op.  */
  transient private XNodeSet m_exprObj;
  
  private boolean m_mustHardReset = false;
  private boolean m_canDetachNodeset = true;

  /**
   * This function is used to fixup variables from QNames to stack frame 
   * indexes at stylesheet build time.
   * @param vars List of QNames that correspond to variables.  This list 
   * should be searched backwards for the first qualified name that 
   * corresponds to the variable reference qname.  The position of the 
   * QName in the vector from the start of the vector will be its position 
   * in the stack frame (but variables above the globalsTop value will need 
   * to be offset to the current stack frame).
   */
  public void fixupVariables(java.util.Vector vars, int globalsSize)
  {
    super.fixupVariables(vars, globalsSize);
    m_expr.fixupVariables(vars, globalsSize);
  }
  
  /**
   * Get the inner contained expression of this filter.
   */
  public Expression getInnerExpression()
  {
  	return m_expr;
  }
  
  /**
   * Set the inner contained expression of this filter.
   */
  public void setInnerExpression(Expression expr)
  {
  	expr.exprSetParent(this);
  	m_expr = expr;
  }

  
  /** 
   * Get the analysis bits for this walker, as defined in the WalkerFactory.
   * @return One of WalkerFactory#BIT_DESCENDANT, etc.
   */
  public int getAnalysisBits()
  {
      if (null != m_expr && m_expr instanceof PathComponent)
      {
        return ((PathComponent) m_expr).getAnalysisBits();
      }
      return WalkerFactory.BIT_FILTER;
  }
  
  /**
   * 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 true as a default.
   */
  public boolean isDocOrdered()
  {
    return m_exprObj.isDocOrdered();
  }
  
  /**
   * Returns the axis being iterated, if it is known.
   * 
   * @return Axis.CHILD, etc., or -1 if the axis is not known or is of multiple 
   * types.
   */
  public int getAxis()
  {
    return m_exprObj.getAxis();
  }
  
  class filterExprOwner implements ExpressionOwner
  {
      /**
     * @see ExpressionOwner#getExpression()
     */
    public Expression getExpression()
    {
      return m_expr;
    }

    /**
     * @see ExpressionOwner#setExpression(Expression)
     */
    public void setExpression(Expression exp)
    {
    	exp.exprSetParent(FilterExprWalker.this);
    	m_expr = exp;
    }
  }
  
	/**
	 * This will traverse the heararchy, calling the visitor for 
	 * each member.  If the called visitor method returns 
	 * false, the subtree should not be called.
	 * 
	 * @param visitor The visitor whose appropriate method will be called.
	 */
	public void callPredicateVisitors(XPathVisitor visitor)
	{
	  m_expr.callVisitors(new filterExprOwner(), visitor);
	  
	  super.callPredicateVisitors(visitor);
	} 


    /**
     * @see Expression#deepEquals(Expression)
     */
    public boolean deepEquals(Expression expr)
    {
      if (!super.deepEquals(expr))
                return false;

      FilterExprWalker walker = (FilterExprWalker)expr;
      if(!m_expr.deepEquals(walker.m_expr))
      	return false;

      return true;
    }

	
}