/*
 * Copyright (c) 2008, the JUNG Project and the Regents of the University
 * of California
 * All rights reserved.
 *
 * This software is open-source under the BSD license; see either
 * "license.txt" or
 * http://jung.sourceforge.net/license.txt 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;
    }
}