/*
 * 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.protocol.http.servlet;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;

import org.apache.wicket.Application;
import org.apache.wicket.Session;
import org.apache.wicket.ThreadContext;
import org.apache.wicket.protocol.http.WebApplication;
import org.apache.wicket.protocol.http.WicketFilter;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * This filter can be used to make the Wicket {@link org.apache.wicket.protocol.http.WebSession}
 * instances available to non-wicket servlets.
 * <p>
 * The following example shows how this filter is setup to for a servlet. You can find the example
 * in the wicket-examples project.
 * 
 * <pre>
 *  <!-- The WicketSesionFilter can be used to provide thread local access to servlets/ JSPs/ etc -->
 *  <filter>
 *    <filter-name>WicketSessionFilter</filter-name>
 *    <filter-class>org.apache.wicket.protocol.http.servlet.WicketSessionFilter</filter-class>
 *    <init-param>
 *      <param-name>filterName</param-name>
 *      <!-- expose the session of the input example app -->
 *      <param-value>FormInputApplication</param-value>
 *    </init-param>
 *  </filter>
 * 
 *  <!-- couple the session filter to the helloworld servlet -->
 *  <filter-mapping>
 *    <filter-name>WicketSessionFilter</filter-name>
 *    <url-pattern>/helloworldservlet/*</url-pattern>
 *  </filter-mapping>
 *  ...
 * 
 *  <servlet>
 *    <servlet-name>HelloWorldServlet</servlet-name>
 *    <servlet-class>org.apache.wicket.examples.HelloWorldServlet</servlet-class>
 *  </servlet>
 * 
 *  <servlet-mapping>
 *    <servlet-name>HelloWorldServlet</servlet-name>
 *    <url-pattern>/helloworldservlet/*</url-pattern>
 *  </servlet-mapping>
 * </pre>
 * 
 * Note: If both {@link WicketFilter} and {@link WicketSessionFilter} are mapped to the same url
 * pattern, make sure to have the {@code <filter-mapping>} for {@link WicketFilter} first in your
 * {@code web.xml}.
 * <p>
 * After that, you can get to the Wicket session in the usual fashion:
 * 
 * <pre>
 * if (Session.exists())
 * {
 * 	Session wicketSession = Session.get();
 * }
 * </pre>
 * 
 * Make sure to test for session existence first, like the HelloWorldServlet does:
 * 
 * <pre>
 * public class HelloWorldServlet extends HttpServlet
 * {
 * 	public void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException,
 * 		IOException
 * 	{
 * 		res.setContentType("text/html");
 * 		PrintWriter out = res.getWriter();
 * 		String message = "Hi. " +
 * 			(Session.exists() ? " I know Wicket session " + Session.get() + "."
 * 				: " I can't find a Wicket session.");
 * 		out.println(message);
 * 		out.close();
 * 	}
 * }
 * </pre>
 * 
 * </p>
 * 
 * @author Eelco Hillenius
 */
public class WicketSessionFilter implements Filter
{
	/** log. */
	private static final Logger logger = LoggerFactory.getLogger(WicketSessionFilter.class);

	/** the filter name/ application key. */
	private String filterName;

	/** the session key where the Wicket session should be stored. */
	private String sessionKey;

	/**
	 * Construct.
	 */
	public WicketSessionFilter()
	{
	}

	/**
	 * @see javax.servlet.Filter#init(javax.servlet.FilterConfig)
	 */
	@Override
	public void init(FilterConfig filterConfig) throws ServletException
	{
		filterName = filterConfig.getInitParameter("filterName");

		if (filterName == null)
		{
			throw new ServletException(
				"you must provide init parameter 'filterName if you want to use " +
					getClass().getName());
		}

		logger.debug("filterName/application key set to {}", filterName);
	}

	/**
	 * @see javax.servlet.Filter#doFilter(javax.servlet.ServletRequest,
	 *      javax.servlet.ServletResponse, javax.servlet.FilterChain)
	 */
	@Override
	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
		throws IOException, ServletException
	{
		try
		{
			WebApplication application = bindApplication();
			bindSession(request, application);
			chain.doFilter(request, response);
		}
		finally
		{
			cleanupBoundApplicationAndSession();
		}
	}

	private void cleanupBoundApplicationAndSession()
	{
		ThreadContext.detach();
	}

	private void bindSession(ServletRequest request, WebApplication application)
	{
		// find wicket session and bind it to thread

		HttpSession httpSession = ((HttpServletRequest)request).getSession(false);
		Session session = getSession(httpSession, application);
		if (session == null)
		{
			if (logger.isDebugEnabled())
			{
				logger.debug("could not set Wicket session: key " + sessionKey +
					" not found in http session for " +
					((HttpServletRequest)request).getContextPath() + "," + request.getServerName() +
					", or http session does not exist");
			}
		}
		else
		{
			ThreadContext.setSession(session);
		}
	}

	private WebApplication bindApplication()
	{
		// find wicket application and bind it to thread

		WebApplication application = (WebApplication)Application.get(filterName);
		if (application == null)
		{
			throw new IllegalStateException("Could not find wicket application mapped to filter: " +
				filterName +
				". Make sure you set filterName attribute to the name of the wicket filter " +
				"for the wicket application whose session you want to access.");
		}
		ThreadContext.setApplication(application);
		return application;
	}

	private Session getSession(HttpSession session, WebApplication application)
	{
		if (session != null)
		{
			if (sessionKey == null)
			{
				sessionKey = application.getSessionAttributePrefix(null, filterName) +
					Session.SESSION_ATTRIBUTE_NAME;

				logger.debug("will use {} as the session key to get the Wicket session", sessionKey);
			}

			return (Session)session.getAttribute(sessionKey);
		}
		return null;
	}

	/**
	 * @see javax.servlet.Filter#destroy()
	 */
	@Override
	public void destroy()
	{
	}
}