/*******************************************************************************
 * Copyright (c) 2002, 2006 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *     Jens Lukowski/Innoopract - initial renaming/restructuring
 *     
 *******************************************************************************/
package org.eclipse.wst.xml.ui.internal.catalog;

import java.io.IOException;
import java.io.InputStream;
import java.net.URL;

import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;

import org.eclipse.wst.xml.ui.internal.Logger;
import org.xml.sax.Attributes;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;

/**
 * 
 */
public class XMLQuickScan {
	public static String getTargetNamespaceURIForSchema(String uri) {
		String result = null;
		try {
			URL url = new URL(uri);
			InputStream inputStream = url.openStream();
			result = XMLQuickScan.getTargetNamespaceURIForSchema(inputStream);
		}
		catch (Exception e) {
		}
		return result;
	}

	public static String getTargetNamespaceURIForSchema(InputStream input) {
		TargetNamespaceURIContentHandler handler = new TargetNamespaceURIContentHandler();
		ClassLoader prevClassLoader = Thread.currentThread().getContextClassLoader();
		try {
			Thread.currentThread().setContextClassLoader(XMLQuickScan.class.getClassLoader());
			SAXParserFactory factory = SAXParserFactory.newInstance();
			factory.setNamespaceAware(true);
			SAXParser parser = factory.newSAXParser();
			parser.parse(new InputSource(input), handler);
		}
		catch (StopParseException e) {
			// this is a normal exception to stop parsing early,
			// when info is found, so we can safely ignore
		}
		catch (ParserConfigurationException e) {
			Logger.logException(e);
		}
		catch (SAXException e) {
			Logger.logException(e);
		}
		catch (IOException e) {
			Logger.logException(e);
		}
		finally {
			Thread.currentThread().setContextClassLoader(prevClassLoader);
		}
		return handler.targetNamespaceURI;
	}

	/**
	 * This is a special exception that is used to stop parsing when required
	 * information is found.
	 */
	static class StopParseException extends org.xml.sax.SAXException {
		static final long serialVersionUID = 1L;

		/**
		 * Constructor StopParseException.
		 */
		StopParseException() {
			super("targetnamespace found, no need to continue the parse");
		}
	}

	static class TargetNamespaceURIContentHandler extends DefaultHandler {
		public String targetNamespaceURI;

		public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {
			if (localName.equals("schema")) //$NON-NLS-1$
			{
				int nAttributes = attributes.getLength();
				for (int i = 0; i < nAttributes; i++) {
					if (attributes.getLocalName(i).equals("targetNamespace")) //$NON-NLS-1$
					{
						targetNamespaceURI = attributes.getValue(i);
						break;
					}
				}
			}
			throw new StopParseException();
		}
	}
}