/*
    * Copyright (c) 2008, The JUNG Authors
    *
    * All rights reserved.
    *
    * This software is open-source under the BSD license; see either
    * "license.txt" or
    * https://github.com/jrtom/jung/blob/master/LICENSE for a description.
    */
  
  package edu.uci.ics.jung.io.graphml.parser;
  
  import java.util.Stack;
  
  import javax.xml.stream.XMLEventReader;
  import javax.xml.stream.events.StartElement;
  import javax.xml.stream.events.XMLEvent;
  
  import edu.uci.ics.jung.io.GraphIOException;
  import edu.uci.ics.jung.io.graphml.ExceptionConverter;
  
  /**
   * Skips an entire unknown subtree of the XML
   *
   * @author Nathan Mittler - nathan.mittler@gmail.com
   */
  public class UnknownElementParser implements ElementParser {
  
      /**
       * Skips an entire subtree starting with the provided unknown element.
       * 
       * @param xmlEventReader
       *            the event reader
       * @param start
       *            the unknown element to be skipped.
       * @return null
       */
      public Object parse(XMLEventReader xmlEventReader, StartElement start)
              throws GraphIOException {
  
          try {
              Stack<String> skippedElements = new Stack<String>();
              skippedElements.add(start.getName().getLocalPart());
  
              while (xmlEventReader.hasNext()) {
  
                  XMLEvent event = xmlEventReader.nextEvent();
                  if (event.isStartElement()) {
  
                      String name = event.asStartElement().getName()
                              .getLocalPart();
  
                      // Push the name of the unknown element.
                      skippedElements.push(name);
                  }
                  if (event.isEndElement()) {
  
                      String name = event.asEndElement().getName()
                              .getLocalPart();
  
                      if (skippedElements.size() == 0
                              || !skippedElements.peek().equals(name)) {
                          throw new GraphIOException(
                                  "Failed parsing GraphML document - startTag/endTag mismatch");
                      }
  
                      // Pop the stack.
                      skippedElements.pop();                        
                      if( skippedElements.isEmpty() ) {
                          break;
                      }
                  }
              }
  
              return null;
  
          } catch (Exception e) {
              ExceptionConverter.convert(e);
          }
  
          return null;
      }
  }