/******************************************************************************* 
 * Copyright (c) 2011, 2012 Red Hat, Inc. 
 *  All rights reserved. 
 * This program is 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: 
 * Red Hat, Inc. - initial API and implementation 
 *
 * @author Innar Made
 ******************************************************************************/
package org.eclipse.bpmn2.modeler.ui;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;

import org.apache.xerces.parsers.SAXParser;
import org.apache.xerces.xni.Augmentations;
import org.apache.xerces.xni.QName;
import org.apache.xerces.xni.XMLAttributes;
import org.apache.xerces.xni.XNIException;
import org.eclipse.bpmn2.modeler.core.model.Bpmn2ModelerResourceImpl;
import org.eclipse.core.resources.IFile;
import org.eclipse.core.resources.IResource;
import org.eclipse.core.runtime.QualifiedName;
import org.eclipse.core.runtime.content.IContentDescription;
import org.eclipse.core.runtime.content.IContentType;
import org.eclipse.core.runtime.content.ITextContentDescriber;
import org.xml.sax.InputSource;

public class Bpmn2ContentDescriber implements ITextContentDescriber {

	private static final String BPMN2_NAMESPACE = "http://www.omg.org/spec/BPMN/20100524/MODEL"; //$NON-NLS-1$
	private static final String ROOT_ELEMENT = "definitions"; //$NON-NLS-1$

	private RootElementParser parser;

	public Bpmn2ContentDescriber() {
	}

	@Override
	public int describe(Reader contents, IContentDescription description) throws IOException {
		return doDescribe(contents) == null ? INVALID : VALID;
	}

	@Override
	public int describe(InputStream contents, IContentDescription description) throws IOException {
		return describe(new InputStreamReader(contents), description);
	}

	private synchronized String doDescribe(Reader contents) throws IOException {
		try {
			InputSource source = new InputSource(contents);
			parser = new RootElementParser();
			parser.parse(source);
		} catch (AcceptedException e) {
			return e.acceptedRootElement;
		} catch (RejectedException e) {
			return null;
		} catch (Exception e) {
			return null;
		} finally {
			parser = null;
		}

		return null;
	}

	@Override
	public QualifiedName[] getSupportedOptions() {
		return null;
	}

	private class RootElementParser extends SAXParser {
		public RootElementParser() {
			fConfiguration.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", false);
		}
		
		@Override
		public void startElement(QName qName, XMLAttributes attributes, Augmentations augmentations)
				throws XNIException {

			super.startElement(qName, attributes, augmentations);

			if (ROOT_ELEMENT.equals(qName.localpart)) {
				String namespace = fNamespaceContext.getURI(qName.prefix);
				if (BPMN2_NAMESPACE.equals(namespace)) {
					throw new AcceptedException(qName.localpart);
				} else {
					throw new RejectedException();
				}
			} else {
				throw new RejectedException();
			}
		}
	}

	private class AcceptedException extends RuntimeException {
		public String acceptedRootElement;

		public AcceptedException(String acceptedRootElement) {
			this.acceptedRootElement = acceptedRootElement;
		}

		private static final long serialVersionUID = 1L;
	}

	private class RejectedException extends RuntimeException {
		private static final long serialVersionUID = 1L;
	}

	public static boolean isBPMN2File(IResource res)
	{
		try
		{
			if (res.getType() == IResource.FILE) {
				IContentDescription desc = ((IFile) res).getContentDescription();
				if (desc != null) {
					IContentType type = desc.getContentType();
					if (type.getId().equals(Bpmn2ModelerResourceImpl.BPMN2_CONTENT_TYPE_ID))
						return true;
				}
			}
		}
		catch(Exception ex)
		{
		}
		return false;
	}
}