/*
 * The Apache Software License, Version 1.1
 *
 *
 * Copyright (c) 1999-2003 The Apache Software Foundation.  All rights 
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer. 
 *
 * 2. 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.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:  
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Xalan" and "Apache Software Foundation" must
 *    not be used to endorse or promote products derived from this
 *    software without prior written permission. For written 
 *    permission, please contact apache@apache.org.
 *
 * 5. Products derived from this software may not be called "Apache",
 *    nor may "Apache" appear in their name, without prior written
 *    permission of the Apache Software Foundation.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED 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 APACHE SOFTWARE FOUNDATION OR
 * ITS 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 Apache Software Foundation and was
 * originally based on software copyright (c) 1999, Lotus
 * Development Corporation., http://www.lotus.com.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */
package org.apache.xalan.extensions;

import javax.xml.transform.ErrorListener;

import org.apache.xpath.objects.XObject;
import org.w3c.dom.Node;
import org.w3c.dom.traversal.NodeIterator;

/**
 * An object that implements this interface can supply
 * information about the current XPath expression context.
 */
public interface ExpressionContext
{

  /**
   * Get the current context node.
   * @return The current context node.
   */
  public Node getContextNode();

  /**
   * Get the current context node list.
   * @return An iterator for the current context list, as
   * defined in XSLT.
   */
  public NodeIterator getContextNodes();
  
  /**
   * Get the error listener.
   * @return The registered error listener.
   */
  public ErrorListener getErrorListener();

  /**
   * Get the value of a node as a number.
   * @param n Node to be converted to a number.  May be null.
   * @return value of n as a number.
   */
  public double toNumber(Node n);

  /**
   * Get the value of a node as a string.
   * @param n Node to be converted to a string.  May be null.
   * @return value of n as a string, or an empty string if n is null.
   */
  public String toString(Node n);

  /**
   * Get a variable based on it's qualified name.
   *
   * @param qname The qualified name of the variable.
   *
   * @return The evaluated value of the variable.
   *
   * @throws javax.xml.transform.TransformerException
   */
  public XObject getVariableOrParam(org.apache.xml.utils.QName qname)
            throws javax.xml.transform.TransformerException;
  
  /**
   * Get the XPathContext that owns this ExpressionContext.
   * 
   * Note: exslt:function requires the XPathContext to access
   * the variable stack and TransformerImpl.
   * 
   * @return The current XPathContext.
   * @throws javax.xml.transform.TransformerException
   */
  public org.apache.xpath.XPathContext getXPathContext()
            throws javax.xml.transform.TransformerException;

}