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;
  
  import javax.xml.transform.ErrorListener;
  import javax.xml.transform.TransformerException;
  
  import org.apache.xalan.res.XSLMessages;
  import org.apache.xml.dtm.DTM;
  import org.apache.xml.dtm.DTMIterator;
  import org.apache.xml.utils.XMLString;
  import org.apache.xpath.objects.XNodeSet;
  import org.apache.xpath.objects.XObject;
  import org.apache.xpath.res.XPATHErrorResources;
  
  import org.xml.sax.ContentHandler;
  
  /**
   * This abstract class serves as the base for all expression objects.  An
   * Expression can be executed to return a {@link org.apache.xpath.objects.XObject},
   * normally has a location within a document or DOM, can send error and warning
   * events, and normally do not hold state and are meant to be immutable once
   * construction has completed.  An exception to the immutibility rule is iterators
   * and walkers, which must be cloned in order to be used -- the original must
   * still be immutable.
   */
  public abstract class Expression implements java.io.Serializable, ExpressionNode, XPathVisitable
  {
      static final long serialVersionUID = 565665869777906902L;
    /**
     * The location where this expression was built from.  Need for diagnostic
     *  messages. May be null.
     *  @serial
     */
    private ExpressionNode m_parent;
  
    /**
     * Tell if this expression or it's subexpressions can traverse outside
     * the current subtree.
     *
     * @return true if traversal outside the context node's subtree can occur.
     */
    public boolean canTraverseOutsideSubtree()
    {
      return false;
    }
    
  //  /**
  //   * Set the location where this expression was built from.
  //   *
  //   *
  //   * @param locator the location where this expression was built from, may be
  //   *                null.
  //   */
  //  public void setSourceLocator(SourceLocator locator)
  //  {
  //    m_slocator = locator;
  //  }
  
    /**
     * Execute an expression in the XPath runtime context, and return the
     * result of the expression.
     *
     *
     * @param xctxt The XPath runtime context.
     * @param currentNode The currentNode.
     *
     * @return The result of the expression in the form of a <code>XObject</code>.
     *
     * @throws javax.xml.transform.TransformerException if a runtime exception
     *         occurs.
     */
    public XObject execute(XPathContext xctxt, int currentNode)
            throws javax.xml.transform.TransformerException
    {
  
      // For now, the current node is already pushed.
      return execute(xctxt);
    }
  
    /**
     * Execute an expression in the XPath runtime context, and return the
     * result of the expression.
     *
     *
     * @param xctxt The XPath runtime context.
     * @param currentNode The currentNode.
     * @param dtm The DTM of the current node.
     * @param expType The expanded type ID of the current node.
     *
     * @return The result of the expression in the form of a <code>XObject</code>.
     *
     * @throws javax.xml.transform.TransformerException if a runtime exception
     *         occurs.
     */
    public XObject execute(
            XPathContext xctxt, int currentNode, DTM dtm, int expType)
              throws javax.xml.transform.TransformerException
    {
  
      // For now, the current node is already pushed.
      return execute(xctxt);
    }
  
    /**
     * Execute an expression in the XPath runtime context, and return the
     * result of the expression.
     *
     *
     * @param xctxt The XPath runtime context.
     *
     * @return The result of the expression in the form of a <code>XObject</code>.
     *
     * @throws javax.xml.transform.TransformerException if a runtime exception
     *         occurs.
     */
    public abstract XObject execute(XPathContext xctxt)
      throws javax.xml.transform.TransformerException;
  
    /**
     * Execute an expression in the XPath runtime context, and return the
     * result of the expression, but tell that a "safe" object doesn't have 
     * to be returned.  The default implementation just calls execute(xctxt).
     *
     *
     * @param xctxt The XPath runtime context.
     * @param destructiveOK true if a "safe" object doesn't need to be returned.
     *
     * @return The result of the expression in the form of a <code>XObject</code>.
     *
     * @throws javax.xml.transform.TransformerException if a runtime exception
     *         occurs.
     */
    public XObject execute(XPathContext xctxt, boolean destructiveOK)
      throws javax.xml.transform.TransformerException
    {
    	return execute(xctxt);
    }
  
  
    /**
     * Evaluate expression to a number.
     *
     *
     * @param xctxt The XPath runtime context.
     * @return The expression evaluated as a double.
     *
     * @throws javax.xml.transform.TransformerException
     */
    public double num(XPathContext xctxt)
            throws javax.xml.transform.TransformerException
    {
      return execute(xctxt).num();
    }
  
    /**
     * Evaluate expression to a boolean.
     *
     *
     * @param xctxt The XPath runtime context.
     * @return false
     *
     * @throws javax.xml.transform.TransformerException
     */
    public boolean bool(XPathContext xctxt)
            throws javax.xml.transform.TransformerException
    {
      return execute(xctxt).bool();
    }
  
    /**
     * Cast result object to a string.
     *
     *
     * @param xctxt The XPath runtime context.
     * @return The string this wraps or the empty string if null
     *
     * @throws javax.xml.transform.TransformerException
     */
    public XMLString xstr(XPathContext xctxt)
            throws javax.xml.transform.TransformerException
    {
      return execute(xctxt).xstr();
    }
  
    /**
     * Tell if the expression is a nodeset expression.  In other words, tell
     * if you can execute {@link #asNode(XPathContext) asNode} without an exception.
     * @return true if the expression can be represented as a nodeset.
     */
    public boolean isNodesetExpr()
    {
      return false;
    }
  
    /**
     * Return the first node out of the nodeset, if this expression is
     * a nodeset expression.
     * @param xctxt The XPath runtime context.
     * @return the first node out of the nodeset, or DTM.NULL.
     *
     * @throws javax.xml.transform.TransformerException
     */
    public int asNode(XPathContext xctxt)
            throws javax.xml.transform.TransformerException
    {
    	DTMIterator iter = execute(xctxt).iter();
      return iter.nextNode();
    }
  
    /**
     * Given an select expression and a context, evaluate the XPath
     * and return the resulting iterator.
     *
     * @param xctxt The execution context.
     * @param contextNode The node that "." expresses.
     *
     *
     * @return A valid DTMIterator.
     * @throws TransformerException thrown if the active ProblemListener decides
     * the error condition is severe enough to halt processing.
     *
     * @throws javax.xml.transform.TransformerException
     * @xsl.usage experimental
     */
    public DTMIterator asIterator(XPathContext xctxt, int contextNode)
            throws javax.xml.transform.TransformerException
    {
  
      try
      {
        xctxt.pushCurrentNodeAndExpression(contextNode, contextNode);
  
        return execute(xctxt).iter();
      }
      finally
      {
        xctxt.popCurrentNodeAndExpression();
      }
    }
    
    /**
     * Given an select expression and a context, evaluate the XPath
     * and return the resulting iterator, but do not clone.
     *
     * @param xctxt The execution context.
     * @param contextNode The node that "." expresses.
     *
     *
     * @return A valid DTMIterator.
     * @throws TransformerException thrown if the active ProblemListener decides
     * the error condition is severe enough to halt processing.
     *
     * @throws javax.xml.transform.TransformerException
     * @xsl.usage experimental
     */
    public DTMIterator asIteratorRaw(XPathContext xctxt, int contextNode)
            throws javax.xml.transform.TransformerException
    {
  
      try
      {
        xctxt.pushCurrentNodeAndExpression(contextNode, contextNode);
  
        XNodeSet nodeset = (XNodeSet)execute(xctxt);
        return nodeset.iterRaw();
      }
      finally
      {
        xctxt.popCurrentNodeAndExpression();
      }
    }
  
  
    /**
     * Execute an expression in the XPath runtime context, and return the
     * result of the expression.
     *
     *
     * @param xctxt The XPath runtime context.
     * NEEDSDOC @param handler
     *
     * @return The result of the expression in the form of a <code>XObject</code>.
     *
     * @throws javax.xml.transform.TransformerException if a runtime exception
     *         occurs.
     * @throws org.xml.sax.SAXException
     */
    public void executeCharsToContentHandler(
            XPathContext xctxt, ContentHandler handler)
              throws javax.xml.transform.TransformerException,
                     org.xml.sax.SAXException
    {
  
      XObject obj = execute(xctxt);
  
      obj.dispatchCharactersEvents(handler);
      obj.detach();
    }
  
    /**
     * Tell if this expression returns a stable number that will not change during 
     * iterations within the expression.  This is used to determine if a proximity 
     * position predicate can indicate that no more searching has to occur.
     * 
     *
     * @return true if the expression represents a stable number.
     */
    public boolean isStableNumber()
    {
      return false;
    }
  
    /**
     * 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).
     * NEEDSDOC @param globalsSize
     */
    public abstract void fixupVariables(java.util.Vector vars, int globalsSize);
    
    /**
     * Compare this object with another object and see 
     * if they are equal, include the sub heararchy.
     * 
     * @param expr Another expression object.
     * @return true if this objects class and the expr
     * object's class are the same, and the data contained 
     * within both objects are considered equal.
     */
    public abstract boolean deepEquals(Expression expr);
    
    /**
     * This is a utility method to tell if the passed in 
     * class is the same class as this.  It is to be used by
     * the deepEquals method.  I'm bottlenecking it here 
     * because I'm not totally confident that comparing the 
     * class objects is the best way to do this.
     * @return true of the passed in class is the exact same 
     * class as this class.
     */
    protected final boolean isSameClass(Expression expr)
    {
    	if(null == expr)
    	  return false;
    	  
    	return (getClass() == expr.getClass());
    }
  
    /**
     * Warn the user of an problem.
     *
     * @param xctxt The XPath runtime context.
     * @param msg An error msgkey that corresponds to one of the conststants found
     *            in {@link org.apache.xpath.res.XPATHErrorResources}, which is
     *            a key for a format string.
     * @param args An array of arguments represented in the format string, which
     *             may be null.
     *
     * @throws TransformerException if the current ErrorListoner determines to
     *                              throw an exception.
     *
     * @throws javax.xml.transform.TransformerException
     */
    public void warn(XPathContext xctxt, String msg, Object[] args)
            throws javax.xml.transform.TransformerException
    {
  
      java.lang.String fmsg = XSLMessages.createXPATHWarning(msg, args);
  
      if (null != xctxt)
      {
        ErrorListener eh = xctxt.getErrorListener();
  
        // TO DO: Need to get stylesheet Locator from here.
        eh.warning(new TransformerException(fmsg, xctxt.getSAXLocator()));
      }
    }
  
    /**
     * Tell the user of an assertion error, and probably throw an
     * exception.
     *
     * @param b  If false, a runtime exception will be thrown.
     * @param msg The assertion message, which should be informative.
     *
     * @throws RuntimeException if the b argument is false.
     *
     * @throws javax.xml.transform.TransformerException
     */
    public void assertion(boolean b, java.lang.String msg)
    {
  
      if (!b)
      {
        java.lang.String fMsg = XSLMessages.createXPATHMessage(
          XPATHErrorResources.ER_INCORRECT_PROGRAMMER_ASSERTION,
          new Object[]{ msg });
  
        throw new RuntimeException(fMsg);
      }
    }
  
    /**
     * Tell the user of an error, and probably throw an
     * exception.
     *
     * @param xctxt The XPath runtime context.
     * @param msg An error msgkey that corresponds to one of the constants found
     *            in {@link org.apache.xpath.res.XPATHErrorResources}, which is
     *            a key for a format string.
     * @param args An array of arguments represented in the format string, which
     *             may be null.
     *
     * @throws TransformerException if the current ErrorListoner determines to
     *                              throw an exception.
     *
     * @throws javax.xml.transform.TransformerException
     */
    public void error(XPathContext xctxt, String msg, Object[] args)
            throws javax.xml.transform.TransformerException
    {
  
      java.lang.String fmsg = XSLMessages.createXPATHMessage(msg, args);
  
      if (null != xctxt)
      {
        ErrorListener eh = xctxt.getErrorListener();
        TransformerException te = new TransformerException(fmsg, this);
  
        eh.fatalError(te);
      }
    }
    
    /**
     * Get the first non-Expression parent of this node.
     * @return null or first ancestor that is not an Expression.
     */
    public ExpressionNode getExpressionOwner()
    {
    	ExpressionNode parent = exprGetParent();
    	while((null != parent) && (parent instanceof Expression))
    		parent = parent.exprGetParent();
    	return parent;
    }
    
    //=============== ExpressionNode methods ================
    
    /** This pair of methods are used to inform the node of its
      parent. */
    public void exprSetParent(ExpressionNode n)
    {
    	assertion(n != this, "Can not parent an expression to itself!");
    	m_parent = n;
    }
    
    public ExpressionNode exprGetParent()
    {
    	return m_parent;
    }
  
    /** This method tells the node to add its argument to the node's
      list of children.  */
    public void exprAddChild(ExpressionNode n, int i)
    {
    	assertion(false, "exprAddChild method not implemented!");
    }
  
    /** This method returns a child node.  The children are numbered
       from zero, left to right. */
    public ExpressionNode exprGetChild(int i)
    {
    	return null;
    }
  
    /** Return the number of children the node has. */
    public int exprGetNumChildren()
    {
    	return 0;
    }
    
    //=============== SourceLocator methods ================
  
    /**
     * Return the public identifier for the current document event.
     *
     * <p>The return value is the public identifier of the document
     * entity or of the external parsed entity in which the markup that
     * triggered the event appears.</p>
     *
     * @return A string containing the public identifier, or
     *         null if none is available.
     * @see #getSystemId
     */
    public String getPublicId()
    {
    	if(null == m_parent)
    	  return null;
    	return m_parent.getPublicId();
    }
  
    /**
     * Return the system identifier for the current document event.
     *
     * <p>The return value is the system identifier of the document
     * entity or of the external parsed entity in which the markup that
     * triggered the event appears.</p>
     *
     * <p>If the system identifier is a URL, the parser must resolve it
     * fully before passing it to the application.</p>
     *
     * @return A string containing the system identifier, or null
     *         if none is available.
     * @see #getPublicId
     */
    public String getSystemId()
    {
    	if(null == m_parent)
    	  return null;
    	return m_parent.getSystemId();
    }
  
    /**
     * Return the line number where the current document event ends.
     *
     * <p><strong>Warning:</strong> The return value from the method
     * is intended only as an approximation for the sake of error
     * reporting; it is not intended to provide sufficient information
     * to edit the character content of the original XML document.</p>
     *
     * <p>The return value is an approximation of the line number
     * in the document entity or external parsed entity where the
     * markup that triggered the event appears.</p>
     *
     * @return The line number, or -1 if none is available.
     * @see #getColumnNumber
     */
    public int getLineNumber()
    {
    	if(null == m_parent)
    	  return 0;
    	return m_parent.getLineNumber();
    }
  
    /**
     * Return the character position where the current document event ends.
     *
     * <p><strong>Warning:</strong> The return value from the method
     * is intended only as an approximation for the sake of error
     * reporting; it is not intended to provide sufficient information
     * to edit the character content of the original XML document.</p>
     *
     * <p>The return value is an approximation of the column number
     * in the document entity or external parsed entity where the
     * markup that triggered the event appears.</p>
     *
     * @return The column number, or -1 if none is available.
     * @see #getLineNumber
     */
    public int getColumnNumber()
    {
    	if(null == m_parent)
    	  return 0;
    	return m_parent.getColumnNumber();
    }
  }
  