/*

 *   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;

import java.util.Set;

/**

 * A Thread task listening for OP_READ events from SocketChannels.

 * @author Christian Lins

 * @since sonews/0.5.0

 */

class ChannelReader extends AbstractDaemon

{

  private static ChannelReader instance = new ChannelReader();

  /**

   * @return Active ChannelReader instance.

   */

  public static ChannelReader getInstance()

  {

    return instance;

  }

  private Selector selector = null;

  protected ChannelReader()

  {

  }

  /**

   * Sets the selector which is used by this reader to determine the channel

   * to read from.

   * @param selector

   */

  public void setSelector(final Selector selector)

  {

    this.selector = selector;

  }

  /**

   * Run loop. Blocks until some data is available in a channel.

   */

  @Override

  public void run()

  {

    assert selector != null;

    while(isRunning())

    {

      try

      {

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

        // processing. There is no need to lock the selector as we have only

        // one thread per selector.

        selector.select();

        // Get list of selection keys with pending events.

        // Note: the selected key set is not thread-safe

        SocketChannel channel = null;

        NNTPConnection conn = null;

        final Set<SelectionKey> selKeys = selector.selectedKeys();

        SelectionKey selKey = null;

        synchronized (selKeys)

        {

          Iterator it = selKeys.iterator();

          // Process the first pending event

          while (it.hasNext())

          {

            selKey = (SelectionKey) it.next();

            channel = (SocketChannel) selKey.channel();

            conn = Connections.getInstance().get(channel);

            // Because we cannot lock the selKey as that would cause a deadlock

            // we lock the connection. To preserve the order of the received

            // byte blocks a selection key for a connection that has pending

            // read events is skipped.

            if (conn == null || conn.tryReadLock())

            {

              // Remove from set to indicate that it's being processed

              it.remove();

              if (conn != null)

              {

                break; // End while loop

              }

            }

            else

            {

              selKey = null;

              channel = null;

              conn = null;

            }

          }

        }

        // Do not lock the selKeys while processing because this causes

        // a deadlock in sun.nio.ch.SelectorImpl.lockAndDoSelect()

        if (selKey != null && channel != null && conn != null)

        {

          processSelectionKey(conn, channel, selKey);

          conn.unlockReadLock();

        }

      }

      catch(CancelledKeyException ex)

      {

        Log.msg("ChannelReader.run(): " + ex, false);

        if(Log.isDebug())

        {

          ex.printStackTrace();

        }

      }

      catch(Exception ex)

      {

        ex.printStackTrace();

      }

      // Eventually wait for a register operation

      synchronized (NNTPDaemon.RegisterGate)

      {

      // Do nothing; FindBugs may warn about an empty synchronized 

      // statement, but we cannot use a wait()/notify() mechanism here.

      // If we used something like RegisterGate.wait() we block here

      // until the NNTPDaemon calls notify(). But the daemon only

      // calls notify() if itself is NOT blocked in the listening socket.

      }

    } // while(isRunning())

  }

  private void processSelectionKey(final NNTPConnection connection,

    final SocketChannel socketChannel, final SelectionKey selKey)

    throws InterruptedException, IOException

  {

    assert selKey != null;

    assert selKey.isReadable();

    // Some bytes are available for reading

    if(selKey.isValid())

    {      

      // Lock the channel

      //synchronized(socketChannel)

      {

        // Read the data into the appropriate buffer

        ByteBuffer buf = connection.getInputBuffer();

        int read = -1;

        try 

        {

          read = socketChannel.read(buf);

        } 

        catch(Exception ex) 

        {

          Log.msg("ChannelReader.processSelectionKey(): " + ex, false);

          if(Log.isDebug())

          {

            ex.printStackTrace();

          }

        }

        if(read == -1) // End of stream

        {

          selKey.cancel();

        }

        else if(read > 0) // If some data was read

        {

          ConnectionWorker.addChannel(socketChannel);

        }

      }

    }

    else

    {

      // Should not happen

      Log.msg(selKey, false);

    }

  }

}