/*
 * 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.resolver;

import org.apache.wicket.Component;
import org.apache.wicket.MarkupContainer;
import org.apache.wicket.Page;
import org.apache.wicket.markup.ComponentTag;
import org.apache.wicket.markup.MarkupException;
import org.apache.wicket.markup.MarkupStream;
import org.apache.wicket.markup.WicketTag;
import org.apache.wicket.markup.html.TransparentWebMarkupContainer;
import org.apache.wicket.markup.html.WebMarkupContainer;
import org.apache.wicket.markup.html.WebPage;
import org.apache.wicket.markup.html.internal.HtmlHeaderContainer;
import org.apache.wicket.markup.html.internal.HtmlHeaderItemsContainer;
import org.apache.wicket.markup.parser.filter.HtmlHeaderSectionHandler;
import org.apache.wicket.markup.parser.filter.WicketTagIdentifier;
import org.apache.wicket.util.resource.IResourceStream;
import org.apache.wicket.util.visit.IVisit;
import org.apache.wicket.util.visit.IVisitor;

/**
 * This is a tag resolver which handles &lt;head&gt; and &lt;wicket:head&gt;tags. It must be
 * registered (with the application) and assumes that a ComponentTag respectively a WicketTag has
 * already been created (see {@link HtmlHeaderSectionHandler} and {@link WicketTagIdentifier}).
 * <p>
 * Provided the current tag is a &lt;head&gt;, a {@link HtmlHeaderContainer} component is created,
 * (auto) added to the component hierarchy and immediately rendered. Please see the javadoc for
 * {@link HtmlHeaderContainer} on how it treats the tag.
 * <p>
 * In case of &lt;wicket:head&gt; a simple {@link TransparentWebMarkupContainer} handles the tag.
 * 
 * @author Juergen Donnerstag
 */
public class HtmlHeaderResolver implements IComponentResolver
{
	private static final long serialVersionUID = 1L;

	/** */
	public static final String HEAD = "head";
	public static final String HEADER_ITEMS = "header-items";

	@Override
	public Component resolve(final MarkupContainer container, final MarkupStream markupStream,
		final ComponentTag tag)
	{
		final Page page = container.getPage();

		// <head> or <wicket:header-items/> component tags have the id == "_header_"
		if (tag.getId().equals(HtmlHeaderSectionHandler.HEADER_ID))
		{
			// Create a special header component which will gather additional
			// input the <head> from 'contributors'.
			return newHtmlHeaderContainer(tag.getId(), tag);
		}
		else if ((tag instanceof WicketTag) && ((WicketTag)tag).isHeadTag())
		{
			// If we found <wicket:head> without surrounding <head> on a Page,
			// then we have to add wicket:head into a automatically generated
			// head first.
			if (container instanceof WebPage)
			{
				HtmlHeaderContainer header = container.visitChildren(new IVisitor<Component, HtmlHeaderContainer>()
				{
					@Override
					public void component(final Component component, final IVisit<HtmlHeaderContainer> visit)
					{
						if (component instanceof HtmlHeaderContainer)
						{
							visit.stop((HtmlHeaderContainer) component);
						} else if (component instanceof TransparentWebMarkupContainer == false)
						{
							visit.dontGoDeeper();
						}
					}
				});

				// It is <wicket:head>. Because they do not provide any
				// additional functionality they are merely a means of surrounding relevant
				// markup. Thus we simply create a WebMarkupContainer to handle
				// the tag (class WicketHeadContainer).
				
				if (header == null)
				{
					// Create a special header component which will gather
					// additional input the <head> from 'contributors'.
					header = newHtmlHeaderContainer(tag.getId(), tag);
					header.add(new WicketHeadContainer());
					return header;
				}

				WicketHeadContainer wicketHeadContainer = 
					header.visitChildren(new FindWicketHeadContainer());
				
				//We just need one WicketHeadContainer, no matter how 
				//many <wicket:head> we have.
				if (wicketHeadContainer == null)
				{
					wicketHeadContainer = new WicketHeadContainer();
					header.add(wicketHeadContainer);
				}
				
				return wicketHeadContainer;
			}
			else if (container instanceof HtmlHeaderContainer)
			{
				// It is <wicket:head>. Because they do not provide any
				// additional functionality there are merely a means of surrounding
				// relevant markup. Thus we simply create a WebMarkupContainer to handle
				// the tag.
				WebMarkupContainer header = new WicketHeadContainer();

				return header;
			}

			final String pageClassName = (page != null) ? page.getClass().getName() : "unknown";
			final IResourceStream stream = markupStream.getResource();
			final String streamName = (stream != null) ? stream.toString() : "unknown";

			throw new MarkupException(
				"Mis-placed <wicket:head>. <wicket:head> must be outside of <wicket:panel>, <wicket:border>, " +
						"and <wicket:extend>. Error occurred while rendering page: " +
					pageClassName + " using markup stream: " + streamName);
		}

		// We were not able to handle the tag
		return null;
	}

	/**
	 * Return a new HtmlHeaderContainer
	 *
	 * @param id
	 * @return HtmlHeaderContainer
	 */
	protected HtmlHeaderContainer newHtmlHeaderContainer(String id, ComponentTag tag)
	{
		HtmlHeaderContainer htmlHeaderContainer;
		if (HtmlHeaderResolver.HEADER_ITEMS.equalsIgnoreCase(tag.getName()))
		{
			htmlHeaderContainer = new HtmlHeaderItemsContainer(id);
		}
		else
		{
			htmlHeaderContainer = new HtmlHeaderContainer(id);
		}

		return htmlHeaderContainer;
	}

	/**
	 * A component for &lt;wicket:head&gt; elements
	 */
	private static class WicketHeadContainer extends WebMarkupContainer
	{
		private static final long serialVersionUID = 1L;

		/**
		 * Constructor.
		 */
		public WicketHeadContainer()
		{
			super(HtmlHeaderSectionHandler.HEADER_ID);

			setRenderBodyOnly(true);
		}
	}
	
	/**
	 * Visitor to find children of type {@link WicketHeadContainer}}
	 */
	private static class FindWicketHeadContainer implements 
			IVisitor<Component, WicketHeadContainer>
	{
		@Override
		public void component(Component component, IVisit<WicketHeadContainer> visit)
		{
			if (component instanceof WicketHeadContainer)
			{
				WicketHeadContainer result = (WicketHeadContainer) component;
				visit.stop(result);
			}
		}	
	}
}
