// ========================================================================
   // Copyright (c) 2008-2009 Mort Bay Consulting Pty. Ltd.
   // ------------------------------------------------------------------------
   // All rights reserved. This program and the accompanying materials
   // are made available under the terms of the Eclipse Public License v1.0
   // and Apache License v2.0 which accompanies this distribution.
   // The Eclipse Public License is available at 
   // http://www.eclipse.org/legal/epl-v10.html
   // The Apache License v2.0 is available at
  // http://www.opensource.org/licenses/apache2.0.php
  // You may elect to redistribute this code under either of these licenses. 
  // ========================================================================
  package com.acme;
  
  import java.io.IOException;
  import java.io.PrintWriter;
  import java.util.HashMap;
  import java.util.LinkedList;
  import java.util.Map;
  import java.util.Queue;
  
  import javax.servlet.ServletException;
  import javax.servlet.http.HttpServlet;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  
  import org.eclipse.jetty.continuation.Continuation;
  import org.eclipse.jetty.continuation.ContinuationSupport;
  
  
  // Simple asynchronous Chat room.
  // This does not handle duplicate usernames or multiple frames/tabs from the same browser
  // Some code is duplicated for clarity.
  public class ChatServlet extends HttpServlet
  {
      
      // inner class to hold message queue for each chat room member
      class Member
      {
          String _name;
          Continuation _continuation;
          Queue<String> _queue = new LinkedList<String>();
      }
  
      Map<String,Map<String,Member>> _rooms = new HashMap<String,Map<String, Member>>();
      
      
      // Handle Ajax calls from browser
      @Override
      protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
      {   
          // Ajax calls are form encoded
          String action = request.getParameter("action");
          String message = request.getParameter("message");
          String username = request.getParameter("user");
  
          if (action.equals("join"))
              join(request,response,username);
          else if (action.equals("poll"))
              poll(request,response,username);
          else if (action.equals("chat"))
              chat(request,response,username,message);
      }
  
      private synchronized void join(HttpServletRequest request,HttpServletResponse response,String username)
      throws IOException
      {
          Member member = new Member();
          member._name=username;
          Map<String,Member> room=_rooms.get(request.getPathInfo());
          if (room==null)
          {
              room=new HashMap<String,Member>();
              _rooms.put(request.getPathInfo(),room);
          }
          room.put(username,member); 
          response.setContentType("text/json;charset=utf-8");
          PrintWriter out=response.getWriter();
          out.print("{action:\"join\"}");
      }
  
      private synchronized void poll(HttpServletRequest request,HttpServletResponse response,String username)
      throws IOException
      {
          Map<String,Member> room=_rooms.get(request.getPathInfo());
          if (room==null)
          {
              response.sendError(503);
              return;
          }
          Member member = room.get(username);
          if (member==null)
          {
              response.sendError(503);
              return;
          }
  
          synchronized(member)
          {
             if (member._queue.size()>0)
             {
                 // Send one chat message
                 response.setContentType("text/json;charset=utf-8");
                 StringBuilder buf=new StringBuilder();
 
                 buf.append("{\"action\":\"poll\",");
                 buf.append("\"from\":\"");
                 buf.append(member._queue.poll());
                 buf.append("\",");
 
                 String message = member._queue.poll();
                 int quote=message.indexOf('"');
                 while (quote>=0)
                 {
                     message=message.substring(0,quote)+'\\'+message.substring(quote);
                     quote=message.indexOf('"',quote+2);
                 }
                 buf.append("\"chat\":\"");
                 buf.append(message);
                 buf.append("\"}");
                 byte[] bytes = buf.toString().getBytes("utf-8");
                 response.setContentLength(bytes.length);
                 response.getOutputStream().write(bytes);
             }
             else 
             {
                 Continuation continuation = ContinuationSupport.getContinuation(request,response);
                 if (continuation.isInitial()) 
                 {
                     // No chat in queue, so suspend and wait for timeout or chat
                     continuation.suspend();
                     member._continuation=continuation;
                 }
                 else
                 {
                     // Timeout so send empty response
                     response.setContentType("text/json;charset=utf-8");
                     PrintWriter out=response.getWriter();
                     out.print("{action:\"poll\"}");
                 }
             }
         }
     }
 
     private synchronized void chat(HttpServletRequest request,HttpServletResponse response,String username,String message)
     throws IOException
     {
         Map<String,Member> room=_rooms.get(request.getPathInfo());
         if (room!=null)
         {
             // Post chat to all members
             for (Member m:room.values())
             {
                 synchronized (m)
                 {
                     m._queue.add(username); // from
                     m._queue.add(message);  // chat
 
                     // wakeup member if polling
                     if (m._continuation!=null)
                     {
                         m._continuation.resume();
                         m._continuation=null;
                     }
                 }
             }
         }
 
         response.setContentType("text/json;charset=utf-8");
         PrintWriter out=response.getWriter();
         out.print("{action:\"chat\"}");  
     }
     
     // Serve the HTML with embedded CSS and Javascript.
     // This should be static content and should use real JS libraries.
     @Override
     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
     {
         if (request.getParameter("action")!=null)
             doPost(request,response);
         else
             getServletContext().getNamedDispatcher("default").forward(request,response);
     }
     
 }