/* Copyright (c) 2002-2011 by XMLVM.org
 *
 * Project Info:  http://www.xmlvm.org
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or
 * (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301,
 * USA.
 */

package org.xmlvm.proc;

import java.io.InputStream;
import java.io.StringWriter;
import java.util.HashMap;
import java.util.Map;

import javax.xml.transform.Result;
import javax.xml.transform.Source;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerConfigurationException;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.URIResolver;
import javax.xml.transform.stream.StreamResult;
import javax.xml.transform.stream.StreamSource;

import net.sf.saxon.Controller;
import net.sf.saxon.jdom.DocumentWrapper;

import org.jdom.Document;
import org.xmlvm.Log;
import org.xmlvm.proc.out.OutputFile;

/**
 * Utility class for running XSL transformations.
 */
public class XsltRunner
{
	private static final String TAG= XsltRunner.class.getSimpleName();
	private static Map<String, Transformer> transformers= new HashMap<String, Transformer>();

	private XsltRunner()
	{
		// Utility class.
	}

	/**
	 * Runs an XSLT file on the given JDOM document.
	 * 
	 * @param xsltFileName
	 *            The name of the file that contains the XSLT definition.
	 * @param doc
	 *            The JDOM document the XSL transformation should be applied to.
	 * @return The output file with the result of the transformation.
	 */
	public static OutputFile runXSLT(String xsltFileName, Document doc)
	{
		return runXSLT(xsltFileName, doc, null);
	}

	/**
	 * Runs an XSLT file on the given JDOM document.
	 * 
	 * @param xsltFileName
	 *            The name of the file that contains the XSLT definition.
	 * @param doc
	 *            The JDOM document the XSL transformation should be applied to.
	 *            The first index refers to the i-th parameter, the index will
	 *            be 0 for the parameter name and 1 for the parameter value. See
	 *            {@link Transformer#setParameter(String, Object)}
	 * @param xsltParams
	 *            Parameters that should be applied to the transformation.
	 * @return The output file with the result of the transformation.
	 */
	public static OutputFile runXSLT(String xsltFileName, Document doc, String[][] xsltParams)
	{
		StringWriter writer= new StringWriter();
		try
		{
			Transformer transformer= getTransformer(xsltFileName);
			transformer.reset();
			if (xsltParams != null)
			{
				for (int i= 0; i < xsltParams.length; i++)
					transformer.setParameter(xsltParams[i][0], xsltParams[i][1]);
			}
			DocumentWrapper docw= new DocumentWrapper(doc, "", ((Controller) transformer).getConfiguration());
			Result result= new StreamResult(writer);
			transformer.transform(docw, result);

			return new OutputFile(writer.toString());
		}
		catch (TransformerException e)
		{
			Log.error(TAG, e.getMessage());
		}
		return null;
	}

	/**
	 * Returns a transformer for the given XSLT file. If one already exists, it
	 * will be returned and no new one will be created.
	 * 
	 * @param xsltFileName
	 *            the name of the XSLT file to use
	 * @return The transformer that uses the given XSLT file or null, if none
	 *         could be created.
	 */
	private static Transformer getTransformer(String xsltFileName)
	{
		String key= xsltFileName + "-" + Thread.currentThread().getId();
		if (transformers.containsKey(key))
		{
			return transformers.get(key);
		}
		InputStream xsltFile= XsltRunner.class.getResourceAsStream("/" + xsltFileName);
		if (xsltFile == null)
		{
			Log.error(TAG, "Error could not find: " + xsltFileName);
			return null;
		}
		try
		{
			Source xsltSource= new StreamSource(xsltFile);
			TransformerFactory transFactory= TransformerFactory.newInstance();

			// Add a URI resolver so that the XSL docs may import other XSL docs
			// using relative paths
			transFactory.setURIResolver(new URIResolver()
			{

				public Source resolve(String href, String base) throws TransformerException
				{
					InputStream is= XsltRunner.class.getResourceAsStream("/" + href);
					return new StreamSource(is);
				}
			});

			Transformer transformer= transFactory.newTransformer(xsltSource);
			transformers.put(key, transformer);
			return transformer;
		}
		catch (TransformerConfigurationException e)
		{
			Log.error(TAG, "Could not create transformer for " + xsltFileName + ": " + e.getMessage());
		}
		return null;
	}
}