/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.wicket.markup.transformer;

import java.io.FileNotFoundException;
import java.io.StringReader;
import java.io.StringWriter;

import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.stream.StreamResult;
import javax.xml.transform.stream.StreamSource;

import org.apache.wicket.Application;
import org.apache.wicket.Component;
import org.apache.wicket.util.resource.IResourceStream;
import org.apache.wicket.core.util.resource.locator.IResourceStreamLocator;


/**
 * A processor to XSLT transform the output generated by a Component.
 * 
 * @see org.apache.wicket.markup.transformer.XsltOutputTransformerContainer
 * @see org.apache.wicket.markup.transformer.XsltTransformerBehavior
 * 
 * @author Juergen Donnerstag
 */
public class XsltTransformer implements ITransformer
{
        private final static String extension = "xsl";

        /** an optional XSL file */
        private final String xslFile;

        /**
         * Construct.
         */
        public XsltTransformer()
        {
                xslFile = null;
        }

        /**
         * Instead of using the default mechanism to determine the associated XSL file, it is given by
         * the user.
         * 
         * @param xslFile
         *            XSL input file path relative to the component's package. If the path does not end
         *            with <tt>.xsl</tt>, then it is considered as a basename and will be passed as-is
         *            to
         *            {@link IResourceStreamLocator#locate(Class, String, String, String, java.util.Locale, String, boolean)}
         *            . All stylesheets must have the <tt>.xsl</tt> extension.
         */
        public XsltTransformer(final String xslFile)
        {
                if ((xslFile != null) && xslFile.endsWith(extension))
                {
                        this.xslFile = xslFile.substring(0, xslFile.length() - extension.length() - 1);
                }
                else
                {
                        this.xslFile = xslFile;
                }
        }

        /**
         * Apply a XSL transformation to the markup generated by a component. The *.xsl resource must be
         * located in the same path as the nearest parent with an associated markup and must have a
         * filename equal to the component's id.
         */
        @Override
        public CharSequence transform(final Component component, final CharSequence output)
                throws Exception
        {
                IResourceStream resourceStream = getResourceStream(component);

                if (resourceStream == null)
                {
                        throw new FileNotFoundException("Unable to find XSLT resource for " +
                                component.toString());
                }

                try
                {
                        // 1. Instantiate a TransformerFactory.
                        TransformerFactory tFactory = TransformerFactory.newInstance();

                        // 2. Use the TransformerFactory to process the stylesheet Source
                        // and
                        // generate a Transformer.
                        Transformer transformer = tFactory.newTransformer(new StreamSource(
                                resourceStream.getInputStream()));

                        // 3. Use the Transformer to transform an XML Source and send the
                        // output to a Result object.
                        StringWriter writer = new StringWriter();
                        transformer.transform(new StreamSource(new StringReader(output.toString())),
                                new StreamResult(writer));

                        return writer.getBuffer();
                }
                finally
                {
                        resourceStream.close();
                }
        }

        /**
         * Get the XSL resource stream
         * 
         * @param component
         * 
         * @return The XSLT file resource stream
         */
        private IResourceStream getResourceStream(final Component component)
        {
                final IResourceStream resourceStream;

                String filePath = xslFile;
                if (filePath == null)
                {
                        filePath = component.findParentWithAssociatedMarkup()
                                .getClass()
                                .getPackage()
                                .getName()
                                .replace('.', '/') +
                                "/" + component.getId();
                }

                resourceStream = Application.get()
                        .getResourceSettings()
                        .getResourceStreamLocator()
                        .locate(getClass(), filePath, component.getStyle(), component.getVariation(),
                                component.getLocale(), XsltTransformer.extension, false);

                return resourceStream;
        }
}