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Pax Wicket Service is an OSGi extension of the Wicket framework, allowing for dynamic loading and unloading of Wicket components and pageSources.
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/*
 * 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.loader;

import java.io.IOException;

import org.apache.wicket.MarkupContainer;
import org.apache.wicket.markup.IMarkupFragment;
import org.apache.wicket.markup.Markup;
import org.apache.wicket.markup.MarkupFactory;
import org.apache.wicket.markup.MarkupNotFoundException;
import org.apache.wicket.markup.MarkupResourceStream;
import org.apache.wicket.markup.MergedMarkup;
import org.apache.wicket.markup.TagUtils;
import org.apache.wicket.util.resource.ResourceStreamNotFoundException;

/**
 * Merge the 2+ markups involved in markup inheritance. From a users perspective there is only one
 * markup associated with the component, the merged one.
 * 
 * @author Juergen Donnerstag
 */
public class InheritedMarkupMarkupLoader implements IMarkupLoader
{
	/**
	 * Constructor.
	 */
	public InheritedMarkupMarkupLoader()
	{
	}

	/**
	 * Load the markup from the resource stream with the base MarkupLoader provided, than check if
	 * markup inheritance must be applied. If yes, than load the base markup and merge them.
	 */
	public final Markup loadMarkup(final MarkupContainer container,
		final MarkupResourceStream markupResourceStream, final IMarkupLoader baseLoader,
		final boolean enforceReload) throws IOException, ResourceStreamNotFoundException
	{
		// read and parse the markup
		Markup markup = baseLoader.loadMarkup(container, markupResourceStream, null, enforceReload);

		// Check if markup contains  which tells us that
		// we need to read the inherited markup as well.
		int extendIndex = requiresBaseMarkup(markup);
		if (extendIndex == -1)
		{
			return markup;
		}

		// Load the base markup
		final Markup baseMarkup = getBaseMarkup(container, markup, enforceReload);
		if ((baseMarkup == null) || (baseMarkup == Markup.NO_MARKUP))
		{
			throw new MarkupNotFoundException(
				"Base markup of inherited markup not found. Component class: " +
					markup.getMarkupResourceStream()
						.getContainerInfo()
						.getContainerClass()
						.getName() +
					". Enable debug messages for org.apache.wicket.util.resource.locator.ResourceStreamLocator to get a list of all filenames tried.");
		}

		// Merge base and derived markup
		return new MergedMarkup(markup, baseMarkup, extendIndex);
	}

	/**
	 * Load the base markup
	 * 
	 * @param container
	 * @param markup
	 * @param enforceReload
	 * @return the base markup
	 */
	private Markup getBaseMarkup(final MarkupContainer container, final Markup markup,
		final boolean enforceReload)
	{
		final Class location = markup.getMarkupResourceStream().getMarkupClass().getSuperclass();

		// get the base markup
		return MarkupFactory.get().getMarkup(container, location, enforceReload);
	}

	/**
	 * Check if markup contains <wicket:extend> which tells us that we need to read the
	 * inherited markup as well. <wicket:extend> MUST BE the first wicket tag in the markup.
	 * Skip raw markup
	 * 
	 * @param markup
	 * @return == 0, if no wicket:extend was found
	 */
	private int requiresBaseMarkup(final IMarkupFragment markup)
	{
		for (int i = 0; i < markup.size(); i++)
		{
			if (TagUtils.isExtendTag(markup, i))
			{
				// Ok, inheritance is on and we must get the
				// inherited markup as well.
				return i;
			}
		}
		return -1;
	}
}