/**
    * Copyright 2005-2006 the original author or authors.
    *
    * Licensed under the Gnu General Pubic 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.opensource.org/licenses/gpl-license.php
    *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
   * See the Gnu General Public License for more details.
   */
  package org.figure8.join.control;
  
  import org.figure8.join.core.ContainerContextHandler;
  import org.figure8.join.core.InvalidParameterException;
  import org.figure8.join.businessobjects.commons.Release;
  import org.figure8.join.businessobjects.reporting.Message;
  import org.figure8.join.businessfacades.commons.IntegrationProcessManager;
  import org.figure8.join.businessfacades.reporting.ReportingManager;
  import org.figure8.join.util.LogUtil;
  
  import org.apache.commons.logging.Log;
  
  import com.sun.syndication.io.FeedException;
  import com.sun.syndication.io.SyndFeedOutput;
  import com.sun.syndication.feed.synd.SyndFeed;
  import com.sun.syndication.feed.synd.SyndEntry;
  import com.sun.syndication.feed.synd.SyndContent;
  import com.sun.syndication.feed.synd.SyndFeedImpl;
  import com.sun.syndication.feed.synd.SyndEntryImpl;
  import com.sun.syndication.feed.synd.SyndContentImpl;
  
  import javax.servlet.http.HttpServlet;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  
  import java.io.IOException;
  import java.util.List;
  import java.util.ArrayList;
  /**
   * This a servlet endpoint for news feed generation and distribution. Each
   * request may contain 2 parameters : <b>type</b> may specify the format of
   * syndication feed wanted by client (rss_0.9, rss_1.0, rss_2.0 and atom_0.3 are
   * currently supported), <b>release</b> may contain the name of release to filter
   * news for.
   * @author  <a href="mailto:laurent.broudoux@free.fr">Laurent Broudoux</a>
   * @version $Revision: 1.1 $
   */
  public class FeedServlet extends HttpServlet{
  
     // Static -------------------------------------------------------------------
     
     /** Get a commons logger. */
     private static final Log log = LogUtil.getLog(FeedServlet.class);
  
     /** Constant denoting the request parameter specifying the type of feed to generate. */
     public static final String FEED_TYPE_PARAM = "type";
     /** Constant denoting the request parameter specifying the release for whom feed should be generated. */
     public static final String RELEASE_PARAM = "release";
  
     /** Constant for the default feed type (RSS 2.0) */
     public static final String DEFAULT_TYPE = "rss_2.0";
     /** Constant for error message returned to client */
     public static final String COULD_NOT_GENERATE_FEED_ERROR = "Could not generate feed for the moment. Service is unavailable.";
  
  
     // Attributes ---------------------------------------------------------------
     
     /** The reporting manager implementation to use for retrieving messages. */
     private ReportingManager reportingManager = null;
     /** The integration process manager to use for retrieving releases. */
     private IntegrationProcessManager processManager = null;
  
  
     // Override of HttpServlet --------------------------------------------------
  
     /**
      * Generate and render a syndication feed depending on request parameters
      * (type and release). See this class Javadoc for more details.
      * @param request The Http request wrapper
      * @param response The Http response wrapper
      * @throws IOException if something wrong occurs during writing of response stream
      */
     public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException{
        try{
           // Retrieve reporting and process managers if necessary.
           initializeManagers();
  
           // Retrieve the release (if specified).
           Release release = null;
           String releaseName = request.getParameter(RELEASE_PARAM);
           if (releaseName != null && releaseName.length() > 0)
              release = processManager.getRelease(releaseName);
  
           if (log.isDebugEnabled())
              log.debug("Generating a syndication feed for release '" + releaseName + "'");
 
          // Retrieve the open messages.
          List messages = reportingManager.getOpenMessages(release);
          SyndFeed feed = createFeed(messages);
 
          // Set the type of this feed from request or apply default type.
          String feedType = request.getParameter(FEED_TYPE_PARAM);
          feedType = (feedType != null) ? feedType : DEFAULT_TYPE;
          feed.setFeedType(feedType);
 
          // Output feed stream onto response writer.
          response.setContentType("text/xml");
          SyndFeedOutput output = new SyndFeedOutput();
          output.output(feed, response.getWriter());
       }
       catch (Exception e){
          // Log exception and tell user that feed cannot be generated.
          log.error("Exception while generating a feed for release: " + request.getParameter(RELEASE_PARAM));
          log.error("Here's the detailed message: " + e.getMessage());
          response.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR, COULD_NOT_GENERATE_FEED_ERROR);
       }
    }
    
    
    // Protected ----------------------------------------------------------------
    
    /**
     * Retrieve the integration process and reporting managers if they have
     * not been initialized yet.
     * @throws InvalidParameterException if they cannot be retrieved
     */
    protected void initializeManagers() throws InvalidParameterException{
       if (reportingManager == null || processManager == null){
          ContainerContextHandler handler = ContainerContextHandler.getInstance();
          processManager = (IntegrationProcessManager)handler.getComponent("processManager");
          reportingManager = (ReportingManager)handler.getComponent("reportingManager");
       }
    }
    
    /**
     * Create a feed using a list of messages.
     * @param messages A list of {@code Message}s
     * @return A SyndicationFeed corresponding to messages.
     */
    protected SyndFeed createFeed(List messages) throws FeedException{
       // Create new feed.
       SyndFeed feed = new SyndFeedImpl();
       feed.setTitle("Integration Portal News Feeds");
       feed.setLink("http://join.sourceforge.net");
       feed.setDescription("This feed has been created using ROME (Java syndication utilities)");
       // Browse messages and add corresponding entries.
       List entries = new ArrayList(messages.size());
       for (int i=0; i < messages.size(); i++){
          Message message = (Message)messages.get(i);
          SyndEntry entry = createFeedEntry(message);
          entries.add(entry);
       }
       feed.setEntries(entries);
       return feed;
    }
    
    /**
     * Create a feed entry from a message.
     * @param message Message to use for creating entry
     * @return A Syndication feed entry
     */
    protected SyndEntry createFeedEntry(Message message) throws FeedException{
       // Create an entry for message.
       SyndEntry entry = new SyndEntryImpl();
       entry.setTitle(message.getTitle());
       entry.setLink(message.getLink());
       entry.setPublishedDate(message.getPublicationDate());
       // Add description to entry.
       SyndContent description = new SyndContentImpl();
       description.setType("text/html");
       description.setValue(message.getContent());
       entry.setDescription(description);
       return entry;
    }
 }