/*
    * $Header$
    * $Revision$
    * $Date$
    *
    * ====================================================================
    *
    * Copyright 2000-2002 bob mcwhirter & James Strachan.
    * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions are
   * met:
   * 
   *   * Redistributions of source code must retain the above copyright
   *     notice, this list of conditions and the following disclaimer.
   * 
   *   * Redistributions in binary form must reproduce the above copyright
   *     notice, this list of conditions and the following disclaimer in the
   *     documentation and/or other materials provided with the distribution.
   * 
   *   * Neither the name of the Jaxen Project nor the names of its
   *     contributors may be used to endorse or promote products derived 
   *     from this software without specific prior written permission.
   * 
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
   * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
   * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
   * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER
   * OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
   * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
   * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
   * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
   * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
   * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
   * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   *
   * ====================================================================
   * This software consists of voluntary contributions made by many 
   * individuals on behalf of the Jaxen Project and was originally 
   * created by bob mcwhirter <bob@werken.com> and 
   * James Strachan <jstrachan@apache.org>.  For more information on the 
   * Jaxen Project, please see <http://www.jaxen.org/>.
   * 
   * $Id$
   */
  
  
  
  package org.jaxen;
  
  import java.util.Iterator;
  import java.util.LinkedList;
  
  import org.jaxen.expr.DefaultXPathFactory;
  import org.jaxen.expr.Expr;
  import org.jaxen.expr.FilterExpr;
  import org.jaxen.expr.FunctionCallExpr;
  import org.jaxen.expr.LocationPath;
  import org.jaxen.expr.Predicate;
  import org.jaxen.expr.Predicated;
  import org.jaxen.expr.Step;
  import org.jaxen.expr.XPathExpr;
  import org.jaxen.expr.XPathFactory;
  import org.jaxen.saxpath.Operator;
  import org.jaxen.saxpath.XPathHandler;
  
  /** SAXPath <code>XPathHandler</code> implementation capable
   *  of building Jaxen expression trees which can walk various
   *  different object models.
   *
   *  @author bob mcwhirter (bob@werken.com)
   */
  public class JaxenHandler implements XPathHandler
  {
      private XPathFactory xpathFactory;
      private XPathExpr    xpath;
      
      /**
       * ????
       */
      protected boolean simplified;
  
      /**
       * This may be changed to an ArrayList in the future (i.e. version &gt;= 1.2). 
       * You really shouldn't be accessing this field directly, but
       * if you are please try to use it as a generic List. Don't use the 
       * methods that are only available in LinkedList.
       */
      protected LinkedList stack;
  
      /** Constructor
       */
      public JaxenHandler()
      {
          this.stack        = new LinkedList();
          this.xpathFactory = new DefaultXPathFactory();
      }
      
     /** Set the Jaxen <code>XPathFactory</code> that constructs
      *  the XPath expression tree during the parse.
      *
      *  @param xpathFactory the factory to use during the parse
      */
     public void setXPathFactory(XPathFactory xpathFactory)
     {
         this.xpathFactory = xpathFactory;
     }
 
     /** Retrieve the Jaxen <code>XPathFactory</code> used
      *  during the parse to construct the XPath expression tree.
      *
      *  @return the <code>XPathFactory</code> used during the parse.
      */
     public XPathFactory getXPathFactory()
     {
         return this.xpathFactory;
     }
 
     /** Retrieve the simplified Jaxen XPath expression tree.
      *
      *  <p>
      *  This method is only valid once <code>XPathReader.parse(...)</code>
      *  successfully returned.
      *  </p>
      *
      *  @return the XPath expression tree
      */
     public XPathExpr getXPathExpr()
     {
         return getXPathExpr( true );
     }
 
     /** Retrieve the Jaxen XPath expression tree, optionally
      *  simplified.
      *
      *  <p>
      *  This method is only valid once <code>XPathReader.parse(...)</code>
      *  successfully returned.
      *  </p>
      *  
      *  @param shouldSimplify ????
      *
      *  @return the XPath expression tree
      */
     public XPathExpr getXPathExpr(boolean shouldSimplify)
     {
         if ( shouldSimplify && ! this.simplified )
         {
             this.xpath.simplify();
             this.simplified = true;
         }
 
         return this.xpath;
     }
 
     public void startXPath()
     {
         this.simplified = false;
         pushFrame();
     }
     
     public void endXPath() throws JaxenException
     {
         this.xpath = getXPathFactory().createXPath( (Expr) pop() );
         popFrame();
     }
 
     public void startPathExpr()
     {
         pushFrame();
     }
 
     public void endPathExpr() throws JaxenException
     {
 
         // PathExpr ::=   LocationPath
         //              | FilterExpr
         //              | FilterExpr / RelativeLocationPath
         //              | FilterExpr // RelativeLocationPath
         //
         // If the current stack-frame has two items, it's a
         // FilterExpr and a LocationPath (of some flavor).
         //
         // If the current stack-frame has one item, it's simply
         // a FilterExpr, and more than likely boils down to a
         // primary expr of some flavor.  But that's for another
         // method...
 
         FilterExpr   filterExpr;
         LocationPath locationPath;
 
         Object       popped;
 
         if ( stackSize() == 2 )
         {
             locationPath = (LocationPath) pop();
             filterExpr   = (FilterExpr) pop();
         }
         else
         {
             popped = pop();
 
             if ( popped instanceof LocationPath )
             {
                 locationPath = (LocationPath) popped;
                 filterExpr   = null;
             }
             else
             {
                 locationPath = null;
                 filterExpr   = (FilterExpr) popped;
             }
         }
         popFrame();
 
         push( getXPathFactory().createPathExpr( filterExpr,
                                                locationPath ) );
     }
 
     public void startAbsoluteLocationPath() throws JaxenException
     {
         pushFrame();
 
         push( getXPathFactory().createAbsoluteLocationPath() );
     }
 
     public void endAbsoluteLocationPath() throws JaxenException
     {
         endLocationPath();
     }
 
     public void startRelativeLocationPath() throws JaxenException
     {
         pushFrame();
 
         push( getXPathFactory().createRelativeLocationPath() );
     }
 
     public void endRelativeLocationPath() throws JaxenException
     {
         endLocationPath();
     }
 
     protected void endLocationPath() throws JaxenException 
     {
         LocationPath path = (LocationPath) peekFrame().removeFirst();
 
         addSteps( path,
                   popFrame().iterator() );
 
         push( path );
     }
 
     protected void addSteps(LocationPath locationPath,
                           Iterator stepIter)
     {
         while ( stepIter.hasNext() )
         {
             locationPath.addStep( (Step) stepIter.next() );
         }
     }
 
     public void startNameStep(int axis,
                               String prefix,
                               String localName) throws JaxenException
     {
         pushFrame();
 
         push( getXPathFactory().createNameStep( axis,
                                                prefix,
                                                localName ) );
     }
 
     public void endNameStep() 
     {
         endStep();
     }
     
     public void startTextNodeStep(int axis) throws JaxenException
     {
         //System.err.println("startTextNodeStep()");
         pushFrame();
         
         push( getXPathFactory().createTextNodeStep( axis ) );
     }
     
     public void endTextNodeStep()
     {
         endStep();
     }
 
     public void startCommentNodeStep(int axis) throws JaxenException
     {
         pushFrame();
 
         push( getXPathFactory().createCommentNodeStep( axis ) );
     }
 
     public void endCommentNodeStep()
     {
         endStep();
     }
         
     public void startAllNodeStep(int axis) throws JaxenException
     {
         pushFrame();
 
         push( getXPathFactory().createAllNodeStep( axis ) );
     }
 
     public void endAllNodeStep()
     {
         endStep();
     }
 
     public void startProcessingInstructionNodeStep(int axis,
                                                    String name) throws JaxenException
     {
         pushFrame();
 
         push( getXPathFactory().createProcessingInstructionNodeStep( axis,
                                                                     name ) );
     }
     
     public void endProcessingInstructionNodeStep()
     {
         endStep();
     }
 
     protected void endStep()
     {
         Step step = (Step) peekFrame().removeFirst();
 
         addPredicates( step,
                        popFrame().iterator() );
 
         push( step );
     }
     
     public void startPredicate()
     {
         pushFrame();
     }
     
     public void endPredicate() throws JaxenException
     {
         Predicate predicate = getXPathFactory().createPredicate( (Expr) pop() );
 
         popFrame();
 
         push( predicate );
     }
 
     public void startFilterExpr() 
     {
         pushFrame();
     }
 
     public void endFilterExpr() throws JaxenException
     {
         Expr expr = (Expr) peekFrame().removeFirst();
         
         FilterExpr filter = getXPathFactory().createFilterExpr( expr );
 
         Iterator predIter = popFrame().iterator();
 
         addPredicates( filter,
                        predIter );
 
         push( filter );
     }
 
     protected void addPredicates(Predicated obj,
                                Iterator predIter)
     {
         while ( predIter.hasNext() )
         {
             obj.addPredicate( (Predicate) predIter.next() );
         }
     }
 
     protected void returnExpr()
     {
         Expr expr = (Expr) pop();
         popFrame();
         push( expr );
     }
 
     public void startOrExpr()
     {
     }
 
     public void endOrExpr(boolean create) throws JaxenException
     {
 
         if ( create )
         {
             Expr rhs = (Expr) pop();
             Expr lhs = (Expr) pop();
 
             push( getXPathFactory().createOrExpr( lhs,
                                                  rhs ) );
         }
     }
 
     public void startAndExpr()
     {
     }
 
     public void endAndExpr(boolean create) throws JaxenException
     {
 
         if ( create )
         {
 
             Expr rhs = (Expr) pop();
             Expr lhs = (Expr) pop();
 
             push( getXPathFactory().createAndExpr( lhs,
                                                   rhs ) );
         }
     }
 
     public void startEqualityExpr()
     {
     }
 
     public void endEqualityExpr(int operator) throws JaxenException
     {
 
         if ( operator != Operator.NO_OP )
         {
             
             Expr rhs = (Expr) pop();
             Expr lhs = (Expr) pop();
             
             push( getXPathFactory().createEqualityExpr( lhs,
                                                         rhs,
                                                         operator ) );
         }
     }
 
     public void startRelationalExpr()
     {
     }
 
     public void endRelationalExpr(int operator) throws JaxenException
     {
 
         if ( operator != Operator.NO_OP )
         {
 
             Expr rhs = (Expr) pop();
             Expr lhs = (Expr) pop();
 
             push( getXPathFactory().createRelationalExpr( lhs,
                                                          rhs,
                                                          operator ) );
         }
     }
 
     public void startAdditiveExpr()
     {
     }
 
     public void endAdditiveExpr(int operator) throws JaxenException
     {
 
         if ( operator != Operator.NO_OP )
         {
             
             Expr rhs = (Expr) pop();
             Expr lhs = (Expr) pop();
             
             push( getXPathFactory().createAdditiveExpr( lhs,
                                                         rhs,
                                                         operator ) );
         }
     }
 
     public void startMultiplicativeExpr()
     {
     }
 
     public void endMultiplicativeExpr(int operator) throws JaxenException
     {
 
         if ( operator != Operator.NO_OP )
         {
 
             Expr rhs = (Expr) pop();
             Expr lhs = (Expr) pop();
             
             push( getXPathFactory().createMultiplicativeExpr( lhs,
                                                              rhs,
                                                              operator ) );
         }
     }
 
     public void startUnaryExpr()
     {
      }
 
     public void endUnaryExpr(int operator) throws JaxenException
     {
 
         if ( operator != Operator.NO_OP )
         {
             push( getXPathFactory().createUnaryExpr( (Expr) pop(),
                                                     operator ) );
         }
     }
 
     public void startUnionExpr() 
     {
     }
 
     public void endUnionExpr(boolean create) throws JaxenException
     {
 
         if ( create )
         {
 
             Expr rhs = (Expr) pop();
             Expr lhs = (Expr) pop();
 
             push( getXPathFactory().createUnionExpr( lhs,
                                                     rhs ) );
         }
     }
 
     public void number(int number) throws JaxenException
     {
         push( getXPathFactory().createNumberExpr( number ) );
     }
 
     public void number(double number) throws JaxenException
     {
         push( getXPathFactory().createNumberExpr( number ) );
     }
 
     public void literal(String literal) throws JaxenException
     {
         push( getXPathFactory().createLiteralExpr( literal ) );
     }
 
     public void variableReference(String prefix,
                                   String variableName) throws JaxenException
     {
         push( getXPathFactory().createVariableReferenceExpr( prefix,
                                                              variableName ) );
     }
 
     public void startFunction(String prefix,
                               String functionName) throws JaxenException
     {
         pushFrame();
         push( getXPathFactory().createFunctionCallExpr( prefix,
                                                         functionName ) );
     }
 
     public void endFunction()
     {
         FunctionCallExpr function = (FunctionCallExpr) peekFrame().removeFirst();
 
         addParameters( function,
                        popFrame().iterator() );
 
         push( function );
     }
 
     protected void addParameters(FunctionCallExpr function,
                                Iterator paramIter)
     {
         while ( paramIter.hasNext() )
         {
             function.addParameter( (Expr) paramIter.next() );
         }
     }
 
     protected int stackSize()
     {
         return peekFrame().size();
     }
 
     protected void push(Object obj)
     {
         peekFrame().addLast( obj );
     }
 
     protected Object pop()
     {
         return peekFrame().removeLast();
     }
 
     protected boolean canPop()
     {
         return ( peekFrame().size() > 0 );
     }
 
     protected void pushFrame()
     {
         this.stack.addLast( new LinkedList() );
     }
 
     protected LinkedList popFrame()
     {
         return (LinkedList) this.stack.removeLast();
     }
 
     protected LinkedList peekFrame()
     {
         return (LinkedList) this.stack.getLast();
     }
 }