/****************************************************************
    * Licensed to the Apache Software Foundation (ASF) under one   *
    * or more contributor license agreements.  See the NOTICE file *
    * distributed with this work for additional information        *
    * regarding copyright ownership.  The ASF licenses this file   *
    * to you under the Apache 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.apache.org/licenses/LICENSE-2.0                 *
   *                                                              *
   * Unless required by applicable law or agreed to in writing,   *
   * software distributed under the License is distributed on an  *
   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY       *
   * KIND, either express or implied.  See the License for the    *
   * specific language governing permissions and limitations      *
   * under the License.                                           *
   ****************************************************************/
  
  package org.apache.james.mpt;
  
  import java.io.IOException;
  import java.net.InetSocketAddress;
  import java.nio.ByteBuffer;
  import java.nio.CharBuffer;
  import java.nio.channels.ServerSocketChannel;
  import java.nio.channels.SocketChannel;
  import java.nio.charset.Charset;
  import java.util.Collection;
  import java.util.Iterator;
  import java.util.LinkedList;
  import java.util.Queue;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  
  /**
   * Simple <a href='http://tools.ietf.org/html/rfc863'>RFC 863</a> implementation.
   */
  public class DiscardProtocol {
  
      private static final Charset ASCII = Charset.forName("US-ASCII");
      
      private static final int SOCKET_CONNECTION_WAIT_MILLIS = 30;
      
      private static final int IDLE_TIMEOUT = 120000;
  
      private static final Log LOG = LogFactory.getLog(DiscardProtocol.class);
      
      /** Serve on this port */
      private final int port;
      
      /** 
       * Queues requests for recordings.
       * Also, used as lock.
       */
      private final Queue<Server> queue;
      
      private final Collection<Server> runningServers;
      
      /** 
       * Server socket when started, null otherwise.
       * Null indicates to the socket serving thread that the server is stopped.
       */
      private volatile ServerSocketChannel socket;
      
  
      public DiscardProtocol(final int port) {
          super();
          this.port = port;
          queue = new LinkedList<Server>();
          runningServers = new LinkedList<Server>();
      }
      
      /**
       * Starts serving.
       * @throws IOException when connection fails
       * @throws IllegalStateException when already started
       */
      public void start() throws IOException {
          synchronized (queue)
          {
              if (socket == null) {
                  socket = ServerSocketChannel.open();
                  socket.socket().bind(new InetSocketAddress(port));
                  // only going to record a single conversation
                  socket.configureBlocking(false);
                  
                  final Thread socketMonitorThread = new Thread(new SocketMonitor());
                  socketMonitorThread.start();
                  
              } else {
                  throw new IllegalStateException("Already started");
              }
          }
      }
      
      
      public Record recordNext() {
         synchronized (queue)
         {
             Server server = new Server();
             queue.add(server);
             return server;
         }
     }
     
     private void abort() {
         synchronized (queue)
         {
             stop();
             for (Iterator it=queue.iterator();it.hasNext();) {
                 final Server server = (Server) it.next();
                 server.abort();
             }
             queue.clear();
         }
     }
     
     /**
      * Stops serving.
      * @return ASCII bytes sent to socket by first
      */
     public void stop() {
         synchronized (queue)
         {
             try {
                 if (socket != null) {
                     if (socket.isOpen()) {
                         socket.close();
                     }
                 }
             } catch (IOException e) {
                 LOG.warn("Failed to close socket", e);
             }
             socket = null;
             for (Iterator it = runningServers.iterator(); it.hasNext();) {
                 final Server server = (Server) it.next();
                 server.abort();
             }
         }
     }
     
     private final class SocketMonitor implements Runnable {
         public void run() {
             try
             {
                 long lastConnection = System.currentTimeMillis();
                 while(socket != null) {
                     final SocketChannel socketChannel = socket.accept();
                     if (socketChannel == null) {
                         if (System.currentTimeMillis() - lastConnection > IDLE_TIMEOUT) {
                             throw new Exception ("Idle timeout");
                         }
                         Thread.sleep(SOCKET_CONNECTION_WAIT_MILLIS);
                     } else {
                         synchronized(queue) {
                             Server nextServer = (Server) queue.poll();
                             if (nextServer == null) {
                                 nextServer = new Server();
                             }
                             nextServer.setSocketChannel(socketChannel);
                             
                             final Thread channelThread = new Thread(nextServer);
                             channelThread.start();
                             runningServers.add(nextServer);
                             lastConnection = System.currentTimeMillis();
                         }
                     }
                 }
             } catch (Exception e) {
                 LOG.fatal("Cannot accept connection", e);
                 abort();
             }
         }
     }
 
     public interface Record {
         /** Blocks until completion of conversation */
         public String complete() throws Exception;
     }
     
     /**
      * Basic server.
      */
     private final static class Server implements Runnable, Record {
 
         private static final int COMPLETION_TIMEOUT = 60000;
 
         private static final int COMPLETION_PAUSE = 1000;
 
         private static final int INITIAL_BUFFER_CAPACITY = 2048;
         
         private final ByteBuffer buffer;
         /**
          * Safe for concurrent access by multiple threads.
          */
         private final StringBuffer out;
         
         /**
          * Initialised by setter 
          */
         private SocketChannel socketChannel;
         
         private volatile boolean aborted;
         private volatile boolean complete;
         
         public Server() {
             complete = false;
             out = new StringBuffer(INITIAL_BUFFER_CAPACITY);
             buffer = ByteBuffer.allocate(INITIAL_BUFFER_CAPACITY);
             aborted = false;
             socketChannel = null;
         }
         
         
         public SocketChannel getSocketChannel() {
             return socketChannel;
         }
         
         public void setSocketChannel(SocketChannel socketChannel) {
             this.socketChannel = socketChannel;
         }
 
         public void run() {
             try
             {
                 if (socketChannel == null)
                 {
                     LOG.fatal("Socket channel must be set before instance is run.");
                 }
                 else
                 {
                     try {
                         while(!socketChannel.finishConnect()) {
                             Thread.sleep(SOCKET_CONNECTION_WAIT_MILLIS);
                         }
                         
                         int read = 0;
                         while(!aborted && socketChannel.isOpen() && read >= 0) {
                             read = socketChannel.read(buffer);
                             if (!buffer.hasRemaining()) {
                                 decant();
                             }
                         }
                         
                     } catch (Exception e) {
                         LOG.fatal("Socket communication failed", e);
                         aborted = true;
                         
                     // Tidy up
                     } finally {
                         try {
                             socketChannel.close();
                         } catch (Exception e) {
                             LOG.debug("Ignoring failure to close socket.", e);
                         }
                     }
                 }
             } finally {
                 synchronized (this)
                 {
                     // Ensure completion is flagged
                     complete = true;
                     // Signal to any waiting threads 
                     notifyAll();
                 }
             }
         }
 
         /**
          * Transfers all data from buffer to builder
          *
          */
         private void decant() {
             buffer.flip();
             final CharBuffer decoded = ASCII.decode(buffer);
             out.append(decoded);
             buffer.clear();
         }
 
 
         public void abort() {
             aborted = true;
         }
         
         /**
          * Blocks until connection is complete (closed)
          */
         public synchronized String complete() throws Exception {
             if (aborted) {
                 throw new Exception("Aborted");
             }
             final long startTime = System.currentTimeMillis();
             boolean isTimedOut = false;
             while (!complete  && !isTimedOut) {
                 wait(COMPLETION_PAUSE);
                 isTimedOut = (System.currentTimeMillis() - startTime) > COMPLETION_TIMEOUT;
             }
             if (isTimedOut && !complete) {
                 throw new Exception("Timed out wait for be notified that read is complete");
             }
             decant();
             return out.toString();
         }        
     }
 }