/*
 * 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.ajax.markup.html;

import java.util.Optional;
import org.apache.wicket.Component;

import org.apache.wicket.ajax.AjaxEventBehavior;
import org.apache.wicket.ajax.AjaxRequestTarget;
import org.apache.wicket.ajax.attributes.AjaxRequestAttributes;
import org.apache.wicket.markup.ComponentTag;
import org.apache.wicket.markup.html.link.Link;
import org.apache.wicket.model.IModel;

/**
 * An ajax link that will degrade to a normal request if ajax is not available or javascript is
 * disabled.
 * 
 * <p>
 * If JavaScript is enabled then the registered JavaScript event 'click' handler will be used,
 * otherwise the 'href' attribute if the markup element is an &lt;a&gt;, &lt;area&gt; or
 * &lt;link&gt;. AjaxFallbackLink doesn't fallback if the markup element is none of the three above.
 * </p>
 * 
 * @since 1.2
 * 
 * @author Igor Vaynberg (ivaynberg)
 * @param <T>
 *            type of model object
 */
public abstract class AjaxFallbackLink<T> extends Link<T>
{
	/** */
	private static final long serialVersionUID = 1L;

	/**
	 * Construct.
	 * 
	 * @param id
	 */
	public AjaxFallbackLink(final String id)
	{
		this(id, null);
	}

	/**
	 * Construct.
	 * 
	 * @param id
	 * @param model
	 */
	public AjaxFallbackLink(final String id, final IModel<T> model)
	{
		super(id, model);

	}

	@Override
	protected void onInitialize()
	{
		super.onInitialize();
		add(newAjaxEventBehavior("click"));
	}

	/**
	 * @param event
	 *            the name of the default event on which this link will listen to
	 * @return the ajax behavior which will be executed when the user clicks the link
	 */
	protected AjaxEventBehavior newAjaxEventBehavior(String event)
	{
		return new AjaxEventBehavior(event)
		{
			private static final long serialVersionUID = 1L;

			@Override
			protected void onEvent(AjaxRequestTarget target)
			{
				onClick(Optional.of(target));
			}

			@Override
			protected void updateAjaxAttributes(AjaxRequestAttributes attributes)
			{
				super.updateAjaxAttributes(attributes);
				attributes.setPreventDefault(true);
				AjaxFallbackLink.this.updateAjaxAttributes(attributes);
			}
			
			@Override
			public boolean getStatelessHint(Component component)
			{				
				return AjaxFallbackLink.this.getStatelessHint();
			}
		};
	}

	/**
	 * @param attributes
	 */
	protected void updateAjaxAttributes(AjaxRequestAttributes attributes)
	{
	}

	@Override
	public final void onClick()
	{
		onClick(Optional.empty());
	}

	/**
	 * Callback for the onClick event. If ajax failed and this event was generated via a normal link
	 * the target argument will be null
	 * 
	 * @param target
	 *            ajax target if this linked was invoked using ajax, null otherwise
	 */
	public abstract void onClick(final Optional<AjaxRequestTarget> target);

	/**
	 * Checks if the tag supports href: a, area or link.
	 * 
	 * @param tag
	 *            the component tag
	 */
	@Override
	protected void onComponentTag(ComponentTag tag)
	{
		super.onComponentTag(tag);

		String tagName = tag.getName();
		if (isEnabledInHierarchy() &&
			!("a".equalsIgnoreCase(tagName) || "area".equalsIgnoreCase(tagName) || "link".equalsIgnoreCase(tagName)))
		{
			String msg = String.format(
				"%s must be used only with <a>, <area> or <link> markup elements. "
					+ "The fallback functionality doesn't work for other markup elements. "
					+ "Component path: %s, markup element: <%s>.",
				AjaxFallbackLink.class.getSimpleName(), getClassRelativePath(), tagName);
			findMarkupStream().throwMarkupException(msg);
		}
	}

	@Override
	protected boolean useJSEventBindingWhenNeeded()
	{
		// AjaxFallbackLink uses Ajax event binding.
		return false;
	}
}
