package at.gv.egovernment.moa.util;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.Vector;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;

import org.w3c.dom.Attr;
import org.w3c.dom.Document;
import org.w3c.dom.DocumentFragment;
import org.w3c.dom.Element;
import org.w3c.dom.NamedNodeMap;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

import org.apache.xerces.parsers.DOMParser;
import org.apache.xerces.parsers.SAXParser;
import org.apache.xerces.parsers.XMLGrammarPreparser;
import org.apache.xerces.util.SymbolTable;
import org.apache.xerces.util.XMLGrammarPoolImpl;
import org.apache.xerces.xni.grammars.XMLGrammarDescription;
import org.apache.xerces.xni.grammars.XMLGrammarPool;
import org.apache.xerces.xni.parser.XMLInputSource;
import org.xml.sax.EntityResolver;
import org.xml.sax.ErrorHandler;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;


import at.gv.egovernment.moa.logging.Logger;

/**
 * Various utility functions for handling XML DOM trees.
 * 
 * The parsing methods in this class make use of some features internal to the
 * Xerces DOM parser, mainly for performance reasons. As soon as JAXP
 * (currently at version 1.2) is better at schema handling, it should be used as
 * the parser interface.
 * 
 * @author Patrick Peck
 * @version $Id$
 */
public class DOMUtils {

  /** Feature URI for namespace aware parsing. */
  private static final String NAMESPACES_FEATURE =
    "http://xml.org/sax/features/namespaces";
  /** Feature URI for validating parsing. */
  private static final String VALIDATION_FEATURE =
    "http://xml.org/sax/features/validation";
  /** Feature URI for schema validating parsing. */
  private static final String SCHEMA_VALIDATION_FEATURE =
    "http://apache.org/xml/features/validation/schema";
  /** Feature URI for normalization of element/attribute values. */
  private static final String NORMALIZED_VALUE_FEATURE =
    "http://apache.org/xml/features/validation/schema/normalized-value";
  /** Feature URI for parsing ignorable whitespace. */
  private static final String INCLUDE_IGNORABLE_WHITESPACE_FEATURE =
    "http://apache.org/xml/features/dom/include-ignorable-whitespace";
  /** Feature URI for creating EntityReference nodes in the DOM tree. */
  private static final String CREATE_ENTITY_REF_NODES_FEATURE =
    "http://apache.org/xml/features/dom/create-entity-ref-nodes";
  /** Property URI for providing external schema locations. */
  private static final String EXTERNAL_SCHEMA_LOCATION_PROPERTY =
    "http://apache.org/xml/properties/schema/external-schemaLocation";
  /** Property URI for providing the external schema location for elements 
   * without a namespace. */
  private static final String EXTERNAL_NO_NAMESPACE_SCHEMA_LOCATION_PROPERTY =
    "http://apache.org/xml/properties/schema/external-noNamespaceSchemaLocation";
  /** Property URI for the Xerces grammar pool. */
  private static final String GRAMMAR_POOL =
    org.apache.xerces.impl.Constants.XERCES_PROPERTY_PREFIX
      + org.apache.xerces.impl.Constants.XMLGRAMMAR_POOL_PROPERTY;
  /** A prime number for initializing the symbol table. */
  private static final int BIG_PRIME = 2039;
  /** Symbol table for the grammar pool. */
  private static SymbolTable symbolTable = new SymbolTable(BIG_PRIME);
  /** Xerces schema grammar pool. */
  private static XMLGrammarPool grammarPool = new XMLGrammarPoolImpl();
  /** Set holding the NamespaceURIs of the grammarPool, to prevent multiple
    * entries of same grammars to the pool */
  private static Set grammarNamespaces; 

  static {
    grammarPool.lockPool();
    grammarNamespaces = new HashSet();
  }

  /**
   * Preparse a schema and add it to the schema pool.
   * The method only adds the schema to the pool if a schema having the same
   * <code>systemId</code> (namespace URI) is not already present in the pool.
   * 
   * @param inputStream An <code>InputStream</code> providing the contents of
   * the schema.
   * @param systemId The systemId (namespace URI) to use for the schema.
   * @throws IOException An error occurred reading the schema.
   */
  public static void addSchemaToPool(InputStream inputStream, String systemId)
    throws IOException {
    XMLGrammarPreparser preparser;

    if (!grammarNamespaces.contains(systemId)) { 

      grammarNamespaces.add(systemId);
    
      // unlock the pool so that we can add another grammar
      grammarPool.unlockPool();
	
      // prepare the preparser
      preparser = new XMLGrammarPreparser(symbolTable);
      preparser.registerPreparser(XMLGrammarDescription.XML_SCHEMA, null);
      preparser.setProperty(GRAMMAR_POOL, grammarPool);
      preparser.setFeature(NAMESPACES_FEATURE, true);
      preparser.setFeature(VALIDATION_FEATURE, true);
	
      // add the grammar to the pool
      preparser.preparseGrammar(
      XMLGrammarDescription.XML_SCHEMA,
        new XMLInputSource(null, systemId, null, inputStream, null));
	
      // lock the pool again so that schemas are not added automatically
      grammarPool.lockPool();
    }
  }

  /**
   * Parse an XML document from an <code>InputStream</code>.
   * 
   * @param inputStream The <code>InputStream</code> containing the XML
   * document.
   * @param validating If <code>true</code>, parse validating.
   * @param externalSchemaLocations A <code>String</code> containing namespace
   * URI to schema location pairs, the same way it is accepted by the <code>xsi:
   * schemaLocation</code> attribute. 
   * @param externalNoNamespaceSchemaLocation The schema location of the
   * schema for elements without a namespace, the same way it is accepted by the
   * <code>xsi:noNamespaceSchemaLocation</code> attribute.
   * @param entityResolver An <code>EntityResolver</code> to resolve external
   * entities (schemas and DTDs). If <code>null</code>, it will not be set.
   * @param errorHandler An <code>ErrorHandler</code> to decide what to do
   * with parsing errors. If <code>null</code>, it will not be set.
   * @return The parsed XML document as a DOM tree.
   * @throws SAXException An error occurred parsing the document.
   * @throws IOException An error occurred reading the document.
   * @throws ParserConfigurationException An error occurred configuring the XML
   * parser.
   */
  public static Document parseDocument(
    InputStream inputStream,
    boolean validating,
    String externalSchemaLocations,
    String externalNoNamespaceSchemaLocation,
    EntityResolver entityResolver,
    ErrorHandler errorHandler)
    throws  SAXException, IOException, ParserConfigurationException {

    DOMParser parser;



		//if Debug is enabled make a copy of inputStream to enable debug output in case of SAXException
		byte buffer [] = null;
		ByteArrayInputStream baStream = null;
		if(true == Logger.isDebugEnabled()) {
			int len = inputStream.available();
			buffer = new byte[len];
			inputStream.read(buffer);
			baStream = new ByteArrayInputStream(buffer);
		}	
			
    // create the DOM parser
    if (symbolTable != null) {
      parser = new DOMParser(symbolTable, grammarPool);
    } else {
      parser = new DOMParser();
    }

    // set parser features and properties
    try {
	    parser.setFeature(NAMESPACES_FEATURE, true);
	    parser.setFeature(VALIDATION_FEATURE, validating);
	    parser.setFeature(SCHEMA_VALIDATION_FEATURE, validating);
	    parser.setFeature(NORMALIZED_VALUE_FEATURE, false);
	    parser.setFeature(INCLUDE_IGNORABLE_WHITESPACE_FEATURE, true);
	    parser.setFeature(CREATE_ENTITY_REF_NODES_FEATURE, false);
	
	    if (validating) {
	      if (externalSchemaLocations != null) {
	        parser.setProperty(
	          EXTERNAL_SCHEMA_LOCATION_PROPERTY,
	          externalSchemaLocations);
	      }
	      if (externalNoNamespaceSchemaLocation != null) {
	        parser.setProperty(
	          EXTERNAL_NO_NAMESPACE_SCHEMA_LOCATION_PROPERTY,
	          externalNoNamespaceSchemaLocation);
	      }
	    }
	
	    // set entity resolver and error handler
	    if (entityResolver != null) {
	      parser.setEntityResolver(entityResolver);
	    }
	    if (errorHandler != null) {
	      parser.setErrorHandler(errorHandler);
	    }
	
	    // parse the document and return it
	    // if debug is enabled: use copy of strem (baStream) else use orig stream
	    if(null != baStream)
	    	parser.parse(new InputSource(baStream));
	    else 
				parser.parse(new InputSource(inputStream));
    } catch(SAXException e) {
			if(true == Logger.isDebugEnabled() && null != buffer) {
				String xmlContent = new String(buffer);
				Logger.debug("SAXException in:\n" + xmlContent);				 
			} 
		  throw(e);
    }

    return parser.getDocument();
  }

  /**
   * Parse an XML document from an <code>InputStream</code>.
   * 
   * It uses a <code>MOAEntityResolver</code> as the <code>EntityResolver</code>
   * and a <code>MOAErrorHandler</code> as the <code>ErrorHandler</code>.
   * 
   * @param inputStream The <code>InputStream</code> containing the XML
   * document.
   * @param validating If <code>true</code>, parse validating.
   * @param externalSchemaLocations A <code>String</code> containing namespace
   * URI to schema location pairs, the same way it is accepted by the <code>xsi:
   * schemaLocation</code> attribute. 
   * @param externalNoNamespaceSchemaLocation The schema location of the
   * schema for elements without a namespace, the same way it is accepted by the
   * <code>xsi:noNamespaceSchemaLocation</code> attribute.
   * @return The parsed XML document as a DOM tree.
   * @throws SAXException An error occurred parsing the document.
   * @throws IOException An error occurred reading the document.
   * @throws ParserConfigurationException An error occurred configuring the XML
   * parser.
   */
  public static Document parseDocument(
    InputStream inputStream,
    boolean validating,
    String externalSchemaLocations,
    String externalNoNamespaceSchemaLocation)
    throws SAXException, IOException, ParserConfigurationException {

    return parseDocument(
      inputStream,
      validating,
      externalSchemaLocations,
      externalNoNamespaceSchemaLocation,
      new MOAEntityResolver(),
      new MOAErrorHandler());
  }

  /**
   * Parse an XML document from a <code>String</code>.
   * 
   * It uses a <code>MOAEntityResolver</code> as the <code>EntityResolver</code>
   * and a <code>MOAErrorHandler</code> as the <code>ErrorHandler</code>.
   * 
   * @param xmlString The <code>String</code> containing the XML document.
   * @param encoding The encoding of the XML document.
   * @param validating If <code>true</code>, parse validating.
   * @param externalSchemaLocations A <code>String</code> containing namespace
   * URI to schema location pairs, the same way it is accepted by the <code>xsi:
   * schemaLocation</code> attribute. 
   * @param externalNoNamespaceSchemaLocation The schema location of the
   * schema for elements without a namespace, the same way it is accepted by the
   * <code>xsi:noNamespaceSchemaLocation</code> attribute.
   * @return The parsed XML document as a DOM tree.
   * @throws SAXException An error occurred parsing the document.
   * @throws IOException An error occurred reading the document.
   * @throws ParserConfigurationException An error occurred configuring the XML
   * parser.
   */
  public static Document parseDocument(
    String xmlString,
    String encoding,
    boolean validating,
    String externalSchemaLocations,
    String externalNoNamespaceSchemaLocation)
    throws SAXException, IOException, ParserConfigurationException {

    InputStream in = new ByteArrayInputStream(xmlString.getBytes(encoding));
    return parseDocument(
      in,
      validating,
      externalSchemaLocations,
      externalNoNamespaceSchemaLocation);
  }

  /**
   * Parse an UTF-8 encoded XML document from a <code>String</code>.
   * 
   * @param xmlString The <code>String</code> containing the XML document.
   * @param validating If <code>true</code>, parse validating.
   * @param externalSchemaLocations A <code>String</code> containing namespace
   * URI to schema location pairs, the same way it is accepted by the <code>xsi:
   * schemaLocation</code> attribute. 
   * @param externalNoNamespaceSchemaLocation The schema location of the
   * schema for elements without a namespace, the same way it is accepted by the
   * <code>xsi:noNamespaceSchemaLocation</code> attribute.
   * @return The parsed XML document as a DOM tree.
   * @throws SAXException An error occurred parsing the document.
   * @throws IOException An error occurred reading the document.
   * @throws ParserConfigurationException An error occurred configuring the XML
   * parser.
   */
  public static Document parseDocument(
    String xmlString,
    boolean validating,
    String externalSchemaLocations,
    String externalNoNamespaceSchemaLocation)
    throws SAXException, IOException, ParserConfigurationException {

    return parseDocument(
      xmlString,
      "UTF-8",
      validating,
      externalSchemaLocations,
      externalNoNamespaceSchemaLocation);
  }

  /**
   * A convenience method to parse an XML document validating.
   * 
   * @param inputStream The <code>InputStream</code> containing the XML
   * document.
   * @return The root element of the parsed XML document.
   * @throws SAXException An error occurred parsing the document.
   * @throws IOException An error occurred reading the document.
   * @throws ParserConfigurationException An error occurred configuring the XML
   * parser.
   */
  public static Element parseXmlValidating(InputStream inputStream)
    throws ParserConfigurationException, SAXException, IOException {
    return DOMUtils
      .parseDocument(inputStream, true, Constants.ALL_SCHEMA_LOCATIONS, null)
      .getDocumentElement();
  }

  /**
   * Schema validate a given DOM element.
   * 
   * @param element The element to validate.
   * @param externalSchemaLocations A <code>String</code> containing namespace
   * URI to schema location pairs, the same way it is accepted by the <code>xsi:
   * schemaLocation</code> attribute. 
   * @param externalNoNamespaceSchemaLocation The schema location of the
   * schema for elements without a namespace, the same way it is accepted by the
   * <code>xsi:noNamespaceSchemaLocation</code> attribute.
   * @return <code>true</code>, if the <code>element</code> validates against
   * the schemas declared in it.
   * @throws SAXException An error occurred parsing the document.
   * @throws IOException An error occurred reading the document from its
   * serialized representation.
   * @throws ParserConfigurationException An error occurred configuring the XML
   * @throws TransformerException An error occurred serializing the element.
   */
  public static boolean validateElement(
    Element element,
    String externalSchemaLocations,
    String externalNoNamespaceSchemaLocation)
    throws
      ParserConfigurationException,
      IOException,
      SAXException,
      TransformerException {

    byte[] docBytes;
    SAXParser parser;

    // create the SAX parser
    if (symbolTable != null) {
      parser = new SAXParser(symbolTable, grammarPool);
    } else {
      parser = new SAXParser();
    }

    // serialize the document
    docBytes = serializeNode(element, "UTF-8");

    // set up parser features and attributes
    parser.setFeature(NAMESPACES_FEATURE, true);
    parser.setFeature(VALIDATION_FEATURE, true);
    parser.setFeature(SCHEMA_VALIDATION_FEATURE, true);
    if (externalSchemaLocations != null) {
      parser.setProperty(
        EXTERNAL_SCHEMA_LOCATION_PROPERTY,
        externalSchemaLocations);
    }
    if (externalNoNamespaceSchemaLocation != null) {
      parser.setProperty(
        EXTERNAL_NO_NAMESPACE_SCHEMA_LOCATION_PROPERTY,
        "externalNoNamespaceSchemaLocation");
    }

    // set up entity resolver and error handler
    parser.setEntityResolver(new MOAEntityResolver());
    parser.setErrorHandler(new MOAErrorHandler());

    // parse validating
    parser.parse(new InputSource(new ByteArrayInputStream(docBytes)));
    return true;
  }

  /**
   * Serialize the given DOM node.
   * 
   * The node will be serialized using the UTF-8 encoding.
   * 
   * @param node The node to serialize.
   * @return String The <code>String</code> representation of the given DOM
   * node.
   * @throws TransformerException An error occurred transforming the
   * node to a <code>String</code>.
   * @throws IOException An IO error occurred writing the node to a byte array.
   */
  public static String serializeNode(Node node)
    throws TransformerException, IOException {
    return new String(serializeNode(node, "UTF-8", false), "UTF-8");
  }


  /**
   * Serialize the given DOM node.
   * 
   * The node will be serialized using the UTF-8 encoding.
   * 
   * @param node The node to serialize.
   * @param omitXmlDeclaration The boolean value for omitting the XML Declaration.
   * @return String The <code>String</code> representation of the given DOM
   * node.
   * @throws TransformerException An error occurred transforming the
   * node to a <code>String</code>.
   * @throws IOException An IO error occurred writing the node to a byte array.
   */
  public static String serializeNode(Node node, boolean omitXmlDeclaration)
    throws TransformerException, IOException {
    return new String(serializeNode(node, "UTF-8", omitXmlDeclaration), "UTF-8");
  }

  /**
   * Serialize the given DOM node to a byte array.
   * 
   * @param node The node to serialize.
   * @param xmlEncoding The XML encoding to use.
   * @return The serialized node, as a byte array. Using a compatible encoding
   * this can easily be converted into a <code>String</code>.
   * @throws TransformerException An error occurred transforming the node to a 
   * byte array.
   * @throws IOException An IO error occurred writing the node to a byte array.
   */
  public static byte[] serializeNode(Node node, String xmlEncoding)
  throws TransformerException, IOException {
    return serializeNode(node, xmlEncoding, false);
  }
  
  /**
   * Serialize the given DOM node to a byte array.
   * 
   * @param node The node to serialize.
   * @param xmlEncoding The XML encoding to use.
   * @param omitXmlDeclaration The boolean value for omitting the XML Declaration.
   * @return The serialized node, as a byte array. Using a compatible encoding
   * this can easily be converted into a <code>String</code>.
   * @throws TransformerException An error occurred transforming the node to a 
   * byte array.
   * @throws IOException An IO error occurred writing the node to a byte array.
   */
  public static byte[] serializeNode(Node node, String xmlEncoding, boolean omitDeclaration)
    throws TransformerException, IOException {

    TransformerFactory transformerFactory = TransformerFactory.newInstance();
    Transformer transformer = transformerFactory.newTransformer();
    ByteArrayOutputStream bos = new ByteArrayOutputStream(16384);

    transformer.setOutputProperty(OutputKeys.METHOD, "xml");
    transformer.setOutputProperty(OutputKeys.ENCODING, xmlEncoding);
    String omit = omitDeclaration ? "yes" : "no";
    transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, omit);
    transformer.transform(new DOMSource(node), new StreamResult(bos));

    bos.flush();
    bos.close();

    return bos.toByteArray();
  }

  /**
    * Return the text that a node contains. 
    * 
    * This routine:
    * <ul>
    * <li>Ignores comments and processing instructions.</li>
    * <li>Concatenates TEXT nodes, CDATA nodes, and the results recursively
    * processing EntityRef nodes.</li>
    * <li>Ignores any element nodes in the sublist. (Other possible options are
    * to recurse into element sublists or throw an exception.)</li>
    * </ul>
    * 
    * @param node A DOM node from which to extract text.
    * @return A String representing its contents.
    */
  public static String getText(Node node) {
    if (!node.hasChildNodes()) {
      return "";
    }

    StringBuffer result = new StringBuffer();
    NodeList list = node.getChildNodes();

    for (int i = 0; i < list.getLength(); i++) {
      Node subnode = list.item(i);
      if (subnode.getNodeType() == Node.TEXT_NODE) {
        result.append(subnode.getNodeValue());
      } else if (subnode.getNodeType() == Node.CDATA_SECTION_NODE) {
        result.append(subnode.getNodeValue());
      } else if (subnode.getNodeType() == Node.ENTITY_REFERENCE_NODE) {
        // Recurse into the subtree for text
        // (and ignore comments)
        result.append(getText(subnode));
      }
    }
    return result.toString();
  }

  /**
   * Build the namespace prefix to namespace URL mapping in effect for a given
   * node.
   * 
   * @param node The context node for which build the map.
   * @return The namespace prefix to namespace URL mapping (
   * a <code>String</code> value to <code>String</code> value mapping).
   */
  public static Map getNamespaceDeclarations(Node node) {
    Map nsDecls = new HashMap();
    int i;

    do {
      if (node.hasAttributes()) {
        NamedNodeMap attrs = node.getAttributes();

        for (i = 0; i < attrs.getLength(); i++) {
          Attr attr = (Attr) attrs.item(i);

          // add prefix mapping if none exists
          if ("xmlns".equals(attr.getPrefix())
            || "xmlns".equals(attr.getName())) {

            String nsPrefix =
              attr.getPrefix() != null ? attr.getLocalName() : "";

            if (nsDecls.get(nsPrefix) == null) {
              nsDecls.put(nsPrefix, attr.getValue());
            }
          }
        }
      }
    } while ((node = node.getParentNode()) != null);

    return nsDecls;
  }

  /**
   * Add all namespace declarations declared in the parent(s) of a given
   * element and used in the subtree of the given element to the given element.  
   * 
   * @param context The element to which to add the namespaces.
   */
  public static void localizeNamespaceDeclarations(Element context) {
    Node parent = context.getParentNode();

    if (parent != null) {
      Map namespaces = getNamespaceDeclarations(context.getParentNode());
      Set nsUris = collectNamespaceURIs(context);
      Iterator iter;

      for (iter = namespaces.entrySet().iterator(); iter.hasNext();) {
        Map.Entry e = (Map.Entry) iter.next();

        if (nsUris.contains(e.getValue())) {
          String prefix = (String) e.getKey();
          String nsUri = (String) e.getValue();
          String nsAttrName = "".equals(prefix) ? "xmlns" : "xmlns:" + prefix;

          context.setAttributeNS(Constants.XMLNS_NS_URI, nsAttrName, nsUri);
        }
      }
    }
  }

  /**
   * Collect all the namespace URIs used in the subtree of a given element.
   * 
   * @param context The element that should be searched for namespace URIs.
   * @return All namespace URIs used in the subtree of <code>context</code>,
   * including the ones used in <code>context</code> itself.
   */
  public static Set collectNamespaceURIs(Element context) {
    Set result = new HashSet();

    collectNamespaceURIsImpl(context, result);
    return result;
  }

  /**
   * A recursive method to do the work of <code>collectNamespaceURIs</code>.
   * 
   * @param context The context element to evaluate.
   * @param result The result, passed as a parameter to avoid unnecessary
   * instantiations of <code>Set</code>.
   */
  private static void collectNamespaceURIsImpl(Element context, Set result) {
    NamedNodeMap attrs = context.getAttributes();
    NodeList childNodes = context.getChildNodes();
    String nsUri;
    int i;

    // add the namespace of the context element
    nsUri = context.getNamespaceURI();
    if (nsUri != null && nsUri != Constants.XMLNS_NS_URI) {
      result.add(nsUri);
    }

    // add all namespace URIs from attributes
    for (i = 0; i < attrs.getLength(); i++) {
      nsUri = attrs.item(i).getNamespaceURI();
      if (nsUri != null && nsUri != Constants.XMLNS_NS_URI) {
        result.add(nsUri);
      }
    }

    // add all namespaces from subelements
    for (i = 0; i < childNodes.getLength(); i++) {
      Node node = childNodes.item(i);

      if (node.getNodeType() == Node.ELEMENT_NODE) {
        collectNamespaceURIsImpl((Element) node, result);
      }
    }
  }

  /**
   * Check, that each attribute node in the given <code>NodeList</code> has its
   * parent in the <code>NodeList</code> as well.
   * 
   * @param nodes The <code>NodeList</code> to check.
   * @return <code>true</code>, if each attribute node in <code>nodes</code>
   * has its parent in <code>nodes</code> as well.
   */
  public static boolean checkAttributeParentsInNodeList(NodeList nodes) {
    Set nodeSet = new HashSet();
    int i;

    // put the nodes into the nodeSet
    for (i = 0; i < nodes.getLength(); i++) {
      nodeSet.add(nodes.item(i));
    }

    // check that each attribute node's parent is in the node list
    for (i = 0; i < nodes.getLength(); i++) {
      Node n = nodes.item(i);

      if (n.getNodeType() == Node.ATTRIBUTE_NODE) {
        Attr attr = (Attr) n;
        Element owner = attr.getOwnerElement();

        if (owner == null) {
          if (!isNamespaceDeclaration(attr)) {
            return false;
          }
        }

        if (!nodeSet.contains(owner) && !isNamespaceDeclaration(attr)) {
          return false;
        }
      }
    }

    return true;
  }

  /**
   * Convert an unstructured <code>NodeList</code> into a 
   * <code>DocumentFragment</code>.
   *
   * @param nodeList Contains the node list to be converted into a DOM 
   * DocumentFragment.
   * @return the resulting DocumentFragment. The DocumentFragment will be 
   * backed by a new DOM Document, i.e. all noded of the node list will be 
   * cloned.
   * @throws ParserConfigurationException An error occurred creating the
   * DocumentFragment.
   * @precondition The nodes in the node list appear in document order.
   * @precondition For each Attr node in the node list, the owning Element is 
   * in the node list as well.
   * @precondition Each Element or Attr node in the node list is namespace 
   * aware.
   */
  public static DocumentFragment nodeList2DocumentFragment(NodeList nodeList)
    throws ParserConfigurationException {

    DocumentBuilder builder =
      DocumentBuilderFactory.newInstance().newDocumentBuilder();
    Document doc = builder.newDocument();
    DocumentFragment result = doc.createDocumentFragment();

    if (null == nodeList || nodeList.getLength() == 0) {
      return result;
    }

    int currPos = 0;
    currPos =
      nodeList2DocumentFragment(nodeList, currPos, result, null, null) + 1;

    while (currPos < nodeList.getLength()) {
      currPos =
        nodeList2DocumentFragment(nodeList, currPos, result, null, null) + 1;
    }
    return result;
  }

  /**
   * Helper method for the <code>nodeList2DocumentFragment</code>.
   * 
   * @param nodeList The <code>NodeList</code> to convert.
   * @param currPos The current position in the <code>nodeList</code>.
   * @param result The resulting <code>DocumentFragment</code>.
   * @param currOrgElem The current original element.
   * @param currClonedElem The current cloned element.
   * @return The current position.
   */
  private static int nodeList2DocumentFragment(
    NodeList nodeList,
    int currPos,
    DocumentFragment result,
    Element currOrgElem,
    Element currClonedElem) {

    while (currPos < nodeList.getLength()) {
      Node currentNode = nodeList.item(currPos);
      switch (currentNode.getNodeType()) {
        case Node.COMMENT_NODE :
        case Node.PROCESSING_INSTRUCTION_NODE :
        case Node.TEXT_NODE :
          {
            // Append current node either to resulting DocumentFragment or to 
            // current cloned Element
            if (null == currClonedElem) {
              result.appendChild(
                result.getOwnerDocument().importNode(currentNode, false));
            } else {
              // Stop processing if current Node is not a descendant of 
              // current Element
              if (!isAncestor(currOrgElem, currentNode)) {
                return --currPos;
              }

              currClonedElem.appendChild(
                result.getOwnerDocument().importNode(currentNode, false));
            }
            break;
          }

        case Node.ELEMENT_NODE :
          {
            Element nextCurrOrgElem = (Element) currentNode;
            Element nextCurrClonedElem =
              result.getOwnerDocument().createElementNS(
                nextCurrOrgElem.getNamespaceURI(),
                nextCurrOrgElem.getNodeName());

            // Append current Node either to resulting DocumentFragment or to 
            // current cloned Element
            if (null == currClonedElem) {
              result.appendChild(nextCurrClonedElem);
              currOrgElem = nextCurrOrgElem;
              currClonedElem = nextCurrClonedElem;
            } else {
              // Stop processing if current Node is not a descendant of
              // current Element
              if (!isAncestor(currOrgElem, currentNode)) {
                return --currPos;
              }

              currClonedElem.appendChild(nextCurrClonedElem);
            }

            // Process current Node (of type Element) recursively
            currPos =
              nodeList2DocumentFragment(
                nodeList,
                ++currPos,
                result,
                nextCurrOrgElem,
                nextCurrClonedElem);

            break;
          }

        case Node.ATTRIBUTE_NODE :
          {
            Attr currAttr = (Attr) currentNode;

            // GK 20030411: Hack to overcome problems with IAIK IXSIL
            if (currAttr.getOwnerElement() == null)
              break;
            if (currClonedElem == null)
              break;

            // currClonedElem must be the owner Element of currAttr if 
            // preconditions are met
            currClonedElem.setAttributeNS(
              currAttr.getNamespaceURI(),
              currAttr.getNodeName(),
              currAttr.getValue());
            break;
          }

        default :
          {
            // All other nodes will be ignored
          }
      }

      currPos++;
    }

    return currPos;
  }

  /**
   * Check, if the given attribute is a namespace declaration.
   * 
   * @param attr The attribute to check.
   * @return <code>true</code>, if the attribute is a namespace declaration,
   * <code>false</code> otherwise.
   */
  private static boolean isNamespaceDeclaration(Attr attr) {
    return Constants.XMLNS_NS_URI.equals(attr.getNamespaceURI());
  }

  /**
   * Check, if a given DOM element is an ancestor of a given node.
   * 
   * @param candAnc The DOM element to check for being the ancestor.
   * @param cand The node to check for being the child.
   * @return <code>true</code>, if <code>candAnc</code> is an (indirect) 
   * ancestor of <code>cand</code>; <code>false</code> otherwise.
   */
  public static boolean isAncestor(Element candAnc, Node cand) {
    Node currPar = cand.getParentNode();

    while (currPar != null) {
      if (candAnc == currPar)
        return true;
      currPar = currPar.getParentNode();
    }
    return false;
  }
  
  /**
   * Selects the (first) element from a node list and returns it.
   * 
   * @param nl  The NodeList to get the element from.
   * @return    The (first) element included in the node list or <code>null</code>
   *            if the node list is <code>null</code> or empty or no element is
   *            included in the list.
   */
  public static Element getElementFromNodeList (NodeList nl) {
    if ((nl == null) || (nl.getLength() == 0)) {
      return null;
    }
    for (int i=0; i<nl.getLength(); i++) {
      Node node = nl.item(i);
      if (node.getNodeType() == Node.ELEMENT_NODE)  {
        return  (Element)node;
      }
    }
    return null;
  }
  
  /**
   * Returns all child elements of the given element.
   * 
   * @param parent  The element to get the child elements from.
   * 
   * @return A list including all child elements of the given element.
   *         Maybe empty if the parent element has no child elements.
   */
  public static List getChildElements (Element parent) {
    Vector v = new Vector();
    NodeList nl = parent.getChildNodes();
    int length = nl.getLength();
    for (int i=0; i < length; i++) {
      Node node = nl.item(i);
      if (node.getNodeType() == Node.ELEMENT_NODE) {
        v.add((Element)node);
      }
    }
    return v;
  }

}