package webIM;

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

/**
 * Title:         Monitor
 * Description:   This servlet is first invoked when the user selects the link of an
 *                online buddy from the buddy list. It receives the buddy's name in
 *                a cookie, and completes the initialization of the conversation.
 *                This first invocation is via the form submitted from the static
 *                page, talk.html.
 *
 *                Afterwards, this servlet receives POST requests from the Talk
 *                frame containing new chat text from the local user. It also receives
 *                GET requests from the buddy's Chat servlet that have a query parameter
 *                equal to the remote filename. Local chat submissions are written to disk
 *                and the filename is added to the newFilesList. The filenames from
 *                remote submissions are added to the newFilesList. The text form
 *                is redisplayed by including talk.jsp.
 * Copyright:    Copyright (c) 2001
 * Company:       UCCS Computer Science Department
 * @author        Merlin Vincent
 * @version 1.0
 */

public class Monitor extends HttpServlet
{
   private static final String CONTENT_TYPE = "text/html";
   private static String endl = System.getProperty("file.separator");

   // A number used to order local files. Filename format: user_buddy_ext
   private int nextLocalFileExt = 0;

   /**Initialize global variables*/
   public void init(ServletConfig config) throws ServletException
   {
      super.init(config);
   }

   /**
    * Process the HTTP Get request. This is NEVER invoked by the local user.
    * The initial GET for the text input form is from a static HTML page
    * rather than from this servlet.
    *
    * This GET is invoked when the remote user's Chat servlet has new text
    * that we should retrieve. This servlet is invoked with:
    *
    * <esi:include src="http://cs.uccs.edu:8064/webIM/Monitor?newChat=buddy_user_n"/>
    *
    */
   public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
   {
      response.setContentType(CONTENT_TYPE);
      PrintWriter out = response.getWriter();
      ServletContext context = getServletContext();
      ArrayList newFilesList = null;

      // Get the newChat query parameter
      String newFile = request.getParameter("newChat").trim();
      if (newFile == null)
         throw new ServletException("Monitor GET: no newRemoteFile parameter");

      /**
       * Parse out the names of the talkers so we can retrieve the global
       * sequence number, whose key is of the form userBuddySeqNo.
       * The new chat filename, e.g., "buddy_user_n".
       */
      int endBuddy = newFile.indexOf("_");
      int endUser = newFile.lastIndexOf("_");

      String buddyName    = newFile.substring(0, endBuddy).trim();
      String userNickName = newFile.substring(endBuddy + 1, endUser).trim();
      String contextKey   = userNickName + buddyName;

      /**
       *  If the buddy submits text before the local user does, the newFilesList
       *  will not exist - create it, and capture the selected buddy's name
       *  and the sequence number that tracks all received/submitted messages.
       */
      newFilesList = (ArrayList) context.getAttribute( contextKey+"NewChat");
      if (newFilesList == null) {
         newFilesList = new ArrayList();
         context.setAttribute( contextKey+"NewChat", newFilesList );
         context.setAttribute( userNickName+"selectedBuddy", buddyName );
         context.setAttribute( contextKey+"SeqNo", new Integer(0));
      }

      // Capture the buddy's filename and bump the sequence number.
      synchronized (newFilesList) {
         newFilesList.add( newFile );
         Integer seqNo = (Integer) context.getAttribute( contextKey+"SeqNo" );
         int sequenceNumber = seqNo.intValue();
         context.setAttribute( contextKey+"SeqNo", new Integer(sequenceNumber + 1));
      }

      // Send an error response so the <esi:include> will fail quickly.
      response.setStatus( HttpServletResponse.SC_NOT_FOUND );
   }

   /**Process the HTTP Post request*/
   public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
   {
      String buddyName = null;
      String userName = null;
      String nickName = null;
      int sequenceNumber = 0;

      HttpSession session = request.getSession(false);
      ServletContext context = getServletContext();
      ArrayList newFilesList = null;

      //Get the submitted text - if none, just redisplay the text input form
      if (request.getContentLength() == 0) {
         RequestDispatcher dispatcher =
            getServletContext().getRequestDispatcher( "/talk.jsp" );
         dispatcher.include(request, response);
         return;
      }

      // Retrieve the existing session and its variables.
      if (session == null)
         throw new ServletException("Monitor POST: no HttpSession");

      userName = (String) session.getAttribute("username");
      if (userName == null)
         throw new ServletException("Monitor POST: no username in session");

      nickName = (String) session.getAttribute("nickname");
      if (userName == null)
         throw new ServletException("Monitor POST: no nickname in session");

      buddyName = (String) context.getAttribute(nickName+"selectedBuddy");
      if (buddyName == null)
         throw new ServletException("Monitor POST: no buddy name in session");

      /**
       * If this is the first call, get the selected buddy's name, init the
       * sequence number that tracks all received/submitted messages, and
       * create the newFilesList to hold the messages.
       */
      if (buddyName.equals("none")) {
         Cookie cookie;
         Cookie[] cookies = request.getCookies();
         if (cookies == null)
            throw new ServletException("Monitor POST: no cookies available");
         for(int i=0; i < cookies.length; i++) {
            cookie = cookies[i];
            if (cookie.getName().equals("selectedBuddy")) {
               buddyName = cookie.getValue().trim();
               break;
            }
         }
         if (buddyName == null)
            throw new ServletException("Monitor POST: no selectedBuddy cookie");

         context.setAttribute(nickName+"selectedBuddy", buddyName);
         context.setAttribute( nickName+buddyName+"SeqNo", new Integer(0));

         newFilesList = new ArrayList();
         context.setAttribute( nickName+buddyName+"NewChat", newFilesList );
      }

      /**
       * Build the local filename for the submitted text. This name always
       * includes the full path, so it starts with a slash. The filenames for
       * remote submissions start with a character, and can be differentiated.
       */
      String filename = new String(
         nickName + "_" + buddyName + "_" + ( nextLocalFileExt++ ));

      String path = new String("/users/server/students/" + userName +"/public_html/webIM/");

      // Get the submitted text and write it to the disk file
      String input = request.getParameter("inputText");
      writeFile((path + filename), input);

      // Add the new file and increment the global sequence number.
      newFilesList = (ArrayList) context.getAttribute( nickName+buddyName+"NewChat");
      if (newFilesList == null)
         throw new ServletException("Monitor POST: no new files list in session");

      synchronized (newFilesList) {
         Integer seqNo = (Integer) context.getAttribute(nickName+buddyName+"SeqNo");
         sequenceNumber = seqNo.intValue();
         context.setAttribute( nickName+buddyName+"SeqNo", new Integer(sequenceNumber + 1));
         newFilesList.add( path + filename );
      }

      // Redisplay the text input form.
      RequestDispatcher dispatcher =
         getServletContext().getRequestDispatcher( "/talk.jsp" );
      dispatcher.include(request, response);
   }

   /**
    * This method writes the text submitted by the user to a disk file
    * named /users/server/students/user/public_html/webIM/user_buddy_<n>
    * where <n> is the message sequence number.
    */
   private void writeFile (String filename, String inputText) throws ServletException {
      File f = null;
      FileOutputStream fos = null;
      try {
         f = new File(filename);
         f.createNewFile();
         if (f.exists() && f.isFile() && f.canWrite()) {
            fos = new FileOutputStream( f );
            byte[] txtBytes = inputText.getBytes();
            fos.write( txtBytes );
            fos.close();
            fos = null;
         }
      } catch (IOException e) {
         throw new ServletException("Monitor writeFile: unable to write file "+ filename);
      }
      finally {
         if (fos != null) {
            try {fos.close();} catch (IOException ioe){}
            fos = null;
         }
         f = null;
      }
   }

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