package webIM;

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.*;

/**
 * Title:         Heartbeat
 * Description:   This servlet periodically receives GET requests from the footer
 *                frame, depending on a JavaScript timer. When new files arrive
 *                they are assigned a sequence number, so the heartbeat can check
 *                the  sequence number to see if something new has arrived. If so,
 *                a JavaScript location.reload() command is issued to cause a
 *                GET request to be sent to refresh the Chat frame.
 * Copyright:    Copyright (c) 2001
 * Company:       UCCS Computer Science Department
 * @author        Merlin Vincent
 * @version 1.0
 */

public class Heartbeat extends HttpServlet
{
   private static final String CONTENT_TYPE = "text/html";

   /**Initialize global variables*/
   public void init(ServletConfig config) throws ServletException
   {
      super.init(config);
   }
   /**Process the HTTP Get request*/
   public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
   {
      RequestDispatcher dispatcher = null;

      response.setContentType(CONTENT_TYPE);
      PrintWriter out = response.getWriter();

      // Get the session and its variables.
      HttpSession session = request.getSession(false);
      if (session == null)
         throw new ServletException("heartbeat GET: no HttpSession");

      String nickName = (String) session.getAttribute("nickname");

      ServletContext context = getServletContext();
      String buddyName = (String) context.getAttribute(nickName+"selectedBuddy");

      // Get newFilesList and global message sequence number from servlet context.
      Integer CurSeqNo = null;
      ArrayList newFilesList = null;
      if (nickName != null && buddyName != null) {
         newFilesList = (ArrayList) context.getAttribute( nickName+buddyName+"NewChat");
         if (newFilesList != null) {
            synchronized (newFilesList) {
               CurSeqNo = (Integer) context.getAttribute( nickName+buddyName+"SeqNo" );
            }
         }
      }

      // If any needed variables are still undefined, just keep heartbeating.
      if (nickName == null || buddyName == null || newFilesList == null || CurSeqNo == null) {
         dispatcher = getServletContext().getRequestDispatcher( "/heartbeat.jsp" );
         dispatcher.include(request, response);
         return;
      }

      // Get the last processed and current message sequence numbers.
      Integer LastSeqNum = (Integer) session.getAttribute("lastHeartbeatSeqNo");
      if (LastSeqNum == null) {
         LastSeqNum = new Integer(0);
      }
      int lastSeqNo = LastSeqNum.intValue();
      int currentSeqNo = CurSeqNo.intValue();

      /**
       * If the chat files list has grown, i.e., the sequence number has
       * increased, we must reload the Chat servlet.
       */
      if (currentSeqNo > lastSeqNo) {
         session.setAttribute( "lastHeartbeatSeqNo", new Integer( currentSeqNo ));

         // Include the JavaScript that reloads the Chat frame
         dispatcher = getServletContext().getRequestDispatcher( "/heartbeat_reload.jsp" );
      }
      else {
         // Include the heartbeat Javascript
         dispatcher = getServletContext().getRequestDispatcher( "/heartbeat.jsp" );
      }
      dispatcher.include(request, response);
   }

   /**Clean up resources*/
   public void destroy()
   {
   }
}