/*

  *   SONEWS News Server

  *   see AUTHORS for the list of contributors

  *

  *   This program is free software: you can redistribute it and/or modify

  *   it under the terms of the GNU General Public License as published by

  *   the Free Software Foundation, either version 3 of the License, or

  *   (at your option) any later version.

  *

  *   This program is distributed in the hope that it will be useful,

  *   but WITHOUT ANY WARRANTY; without even the implied warranty of

  *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

  *   GNU General Public License for more details.

  *

  *   You should have received a copy of the GNU General Public License

  *   along with this program.  If not, see <http://www.gnu.org/licenses/>.

  */

 package org.sonews.daemon;

 import org.sonews.util.Log;

 import java.io.IOException;

 import java.nio.ByteBuffer;

 import java.nio.channels.CancelledKeyException;

 import java.nio.channels.SelectionKey;

 import java.nio.channels.Selector;

 import java.nio.channels.SocketChannel;

 import java.util.Iterator;

 /**

  * A Thread task that processes OP_WRITE events for SocketChannels.

  * @author Christian Lins

  * @since sonews/0.5.0

  */

 class ChannelWriter extends AbstractDaemon

 {

   private static ChannelWriter instance = new ChannelWriter();

   /**

    * @return Returns the active ChannelWriter instance.

    */

   public static ChannelWriter getInstance()

   {

     return instance;

   }

   private Selector selector = null;

   protected ChannelWriter()

   {

   }

   /**

    * @return Selector associated with this instance.

    */

   public Selector getSelector()

   {

     return this.selector;

   }

   /**

    * Sets the selector that is used by this ChannelWriter.

    * @param selector

    */

   public void setSelector(final Selector selector)

   {

     this.selector = selector;

   }

   /**

    * Run loop.

    */

   @Override

   public void run()

   {

     assert selector != null;

     while(isRunning())

     {

       try

       {

         SelectionKey   selKey        = null;

         SocketChannel  socketChannel = null;

         NNTPConnection connection    = null;

         // select() blocks until some SelectableChannels are ready for

         // processing. There is no need to synchronize the selector as we

         // have only one thread per selector.

         selector.select(); // The return value of select can be ignored

         // Get list of selection keys with pending OP_WRITE events.

         // The keySET is not thread-safe whereas the keys itself are.

         Iterator it = selector.selectedKeys().iterator();

         while (it.hasNext())

         {

           // We remove the first event from the set and store it for

           // later processing.

           selKey = (SelectionKey) it.next();

           socketChannel = (SocketChannel) selKey.channel();

           connection = Connections.getInstance().get(socketChannel);

           it.remove();

           if (connection != null)

           {

             break;

           }

           else

           {

             selKey = null;

           }

         }

         if (selKey != null)

         {

           try

           {

             // Process the selected key.

             // As there is only one OP_WRITE key for a given channel, we need

             // not to synchronize this processing to retain the order.

             processSelectionKey(connection, socketChannel, selKey);

           }

           catch (IOException ex)

           {

             Log.msg("Error writing to channel: " + ex, false);

             // Cancel write events for this channel

             selKey.cancel();

             connection.shutdownInput();

             connection.shutdownOutput();

           }

         }

         // Eventually wait for a register operation

         synchronized(NNTPDaemon.RegisterGate) { /* do nothing */ }

       }

       catch(CancelledKeyException ex)

       {

         Log.msg("ChannelWriter.run(): " + ex, true);

       }

       catch(Exception ex)

       {

         ex.printStackTrace();

       }

     } // while(isRunning())

   }

   private void processSelectionKey(final NNTPConnection connection,

     final SocketChannel socketChannel, final SelectionKey selKey)

     throws InterruptedException, IOException

   {

     assert connection != null;

     assert socketChannel != null;

     assert selKey != null;

     assert selKey.isWritable();

     // SocketChannel is ready for writing

     if(selKey.isValid())

     {

       // Lock the socket channel

       synchronized(socketChannel)

       {

         // Get next output buffer

         ByteBuffer buf = connection.getOutputBuffer();

         if(buf == null)

         {

           // Currently we have nothing to write, so we stop the writeable

           // events until we have something to write to the socket channel

           //selKey.cancel();

           selKey.interestOps(0);

           return;

         }

         while(buf != null) // There is data to be send

         {

           // Write buffer to socket channel; this method does not block

           if(socketChannel.write(buf) <= 0)

           {

             // Perhaps there is data to be written, but the SocketChannel's

             // buffer is full, so we stop writing to until the next event.

             break;

           }

           else

           {

             // Retrieve next buffer if available; method may return the same

             // buffer instance if it still have some bytes remaining

             buf = connection.getOutputBuffer();

           }

         }

       }

     }

     else

     {

       Log.msg("Invalid OP_WRITE key: " + selKey, false);

       if (socketChannel.socket().isClosed())

       {

         connection.shutdownInput();

         connection.shutdownOutput();

         socketChannel.close();

         Log.msg("Connection closed.", true);

       }

     }

   }

 }