//
   //  ========================================================================
   //  Copyright (c) 1995-2015 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 org.eclipse.jetty.io;
  
  import java.io.IOException;
  import java.nio.channels.ClosedChannelException;
  import java.nio.channels.ReadPendingException;
  import java.text.SimpleDateFormat;
  import java.util.Date;
  import java.util.concurrent.atomic.AtomicReference;
  
  import org.eclipse.jetty.util.Callback;
  import org.eclipse.jetty.util.log.Log;
  import org.eclipse.jetty.util.log.Logger;
  
  /**
   * A Utility class to help implement {@link EndPoint#fillInterested(Callback)}
   * by keeping state and calling the context and callback objects.
   */
  public abstract class FillInterest
  {
      private final static Logger LOG = Log.getLogger(FillInterest.class);
      private final AtomicReference<Callback> _interested = new AtomicReference<>(null);
      private Throwable _lastSet;
  
      protected FillInterest()
      {
      }
  
      /**
       * Call to register interest in a callback when a read is possible.
       * The callback will be called either immediately if {@link #needsFillInterest()}
       * returns true or eventually once {@link #fillable()} is called.
       *
       * @param callback the callback to register
       * @throws ReadPendingException if unable to read due to pending read op
       */
      public void register(Callback callback) throws ReadPendingException
      {
          if (callback == null)
              throw new IllegalArgumentException();
  
          if (_interested.compareAndSet(null, callback))
          {
              if (LOG.isDebugEnabled())
              {
                  LOG.debug("{} register {}",this,callback);
                  _lastSet=new Throwable(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS").format(new Date()) + ":" + Thread.currentThread().getName());
              }
          }
          else
          {
              LOG.warn("Read pending for {} prevented {}", _interested, callback);
              if (LOG.isDebugEnabled())
                  LOG.warn("callback set at ",_lastSet);
              throw new ReadPendingException();
          }
          try
          {
              if (LOG.isDebugEnabled())
                  LOG.debug("{} register {}",this,callback);
              needsFillInterest();
          }
          catch (Throwable e)
          {
              onFail(e);
          }
      }
  
      /**
       * Call to signal that a read is now possible.
       */
      public void fillable()
      {
          Callback callback = _interested.get();
          if (LOG.isDebugEnabled())
              LOG.debug("{} fillable {}",this,callback);
          if (callback != null && _interested.compareAndSet(callback, null))
              callback.succeeded();
          else if (LOG.isDebugEnabled())
              LOG.debug("{} lost race {}",this,callback);
      }
  
     /**
      * @return True if a read callback has been registered
      */
     public boolean isInterested()
     {
         return _interested.get() != null;
     }
 
     /**
      * Call to signal a failure to a registered interest
      *
      * @param cause the cause of the failure
      * @return true if the cause was passed to a {@link Callback} instance
      */
     public boolean onFail(Throwable cause)
     {
         Callback callback = _interested.get();
         if (callback != null && _interested.compareAndSet(callback, null))
         {
             callback.failed(cause);
             return true;
         }
         return false;
     }
 
     public void onClose()
     {
         Callback callback = _interested.get();
         if (callback != null && _interested.compareAndSet(callback, null))
             callback.failed(new ClosedChannelException());
     }
 
     @Override
     public String toString()
     {
         return String.format("FillInterest@%x{%b,%s}", hashCode(), _interested.get(), _interested.get());
     }
 
     /**
      * Register the read interest
      * Abstract method to be implemented by the Specific ReadInterest to
      * schedule a future call to {@link #fillable()} or {@link #onFail(Throwable)}
      *
      * @throws IOException if unable to fulfill interest in fill
      */
     abstract protected void needsFillInterest() throws IOException;
 }