//
   //  ========================================================================
   //  Copyright (c) 1995-2013 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 java.util.concurrent.atomic.AtomicReference;
  
  import javax.servlet.AsyncContext;
  import javax.servlet.AsyncEvent;
  import javax.servlet.AsyncListener;
  import javax.servlet.ServletException;
  import javax.servlet.http.HttpServlet;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  
  // Simple asynchronous Chat room.
  // This does not handle duplicate usernames or multiple frames/tabs from the same browser
  // Some code is duplicated for clarity.
  @SuppressWarnings("serial")
  public class ChatServlet extends HttpServlet
  {
  
      // inner class to hold message queue for each chat room member
      class Member implements AsyncListener
      {
          final String _name;
          final AtomicReference<AsyncContext> _async=new AtomicReference<>();
          final Queue<String> _queue = new LinkedList<String>();
          
          Member(String name)
          {
              _name=name;
          }
          
          @Override
          public void onTimeout(AsyncEvent event) throws IOException
          {
              AsyncContext async = _async.get();
              if (async!=null && _async.compareAndSet(async,null))
              {
                  HttpServletResponse response = (HttpServletResponse)async.getResponse();
                  response.setContentType("text/json;charset=utf-8");
                  PrintWriter out=response.getWriter();
                  out.print("{action:\"poll\"}");
                  async.complete();
              }
          }
          
          @Override
          public void onStartAsync(AsyncEvent event) throws IOException
          {
              event.getAsyncContext().addListener(this);
          }
          
          @Override
          public void onError(AsyncEvent event) throws IOException
          {
          }
          
          @Override
          public void onComplete(AsyncEvent event) throws IOException
          {
          }
      }
  
      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(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;
         }
         final 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
             {
                 AsyncContext async = request.startAsync();
                 async.setTimeout(10000);
                 async.addListener(member);
                 if (!member._async.compareAndSet(null,async))
                     throw new IllegalStateException();
             }
         }
     }
 
     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
                     AsyncContext async=m._async.get();
                     if (async!=null & m._async.compareAndSet(async,null))
                         async.dispatch();
                 }
             }
         }
 
         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);
     }
 
 }