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/*
 * CancelEvent.java February 2007
 *
 * Copyright (C) 2007, Niall Gallagher 
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation.
 *
 * This library 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 Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General 
 * Public License along with this library; if not, write to the 
 * Free Software Foundation, Inc., 59 Temple Place, Suite 330, 
 * Boston, MA  02111-1307  USA
 */

package org.simpleframework.util.select;

import java.nio.channels.SelectableChannel;

/**
 * The Cancellation object is used to represent a task
 * that can be executed to cancel an operation. This is used in the
 * place of a normal Operation to pass for execution
 * when the operation has expired before the I/O event is was
 * interested in occurred. Before this is executed the operation is
 * removed from selection.
 * 
 * @author Niall Gallagher
 */      
class CancelEvent implements Event {
   
   /**
    * This is the operation that is to be canceled by this event.
    */
   private final Operation task;
   
   /**
    * This is the operation object that is to be canceled.
    */
   private final Event event;
   
   /**
    * Constructor for the Cancellation object. This is
    * used to create a runnable task that delegates to the cancel
    * method of the operation. This will be executed asynchronously
    * by the executor after being removed from selection. 
    * 
    * @param task this is the task that is to be canceled by this
    */
   public CancelEvent(Event event) {
      this.task = event.getOperation();
      this.event = event;
   }
   
   /**
    * This method is executed by the Executor object 
    * if the operation expires before the required I/O event(s)
    * have occurred. It is typically used to shutdown the socket
    * and release any resources associated with the operation.
    */
   public void run() {
      task.cancel();
   } 
   
   /**
    * This is used to get the expiry for the operation. The expiry
    * represents some static time in the future when the event will
    * expire if it does not become ready. This is used to cancel the
    * operation so that it does not remain in the distributor.
    *
    * @return the remaining time this operation will wait for
    */         
   public long getExpiry() {
      return 0;
   }
   
   /**
    * This returns the I/O operations that the event is interested
    * in as an integer bit mask. When any of these operations are
    * ready the distributor will execute the provided operation. 
    * 
    * @return the integer bit mask of interested I/O operations
    */
   public int getInterest() {
      return event.getInterest();
   }

   /**
    * This is the SelectableChannel which is used to 
    * determine if the operation should be executed. If the channel   
    * is ready for a given I/O event it can be run. For instance if
    * the operation is used to perform some form of read operation
    * it can be executed when ready to read data from the channel.
    *
    * @return this returns the channel used to govern execution
    */    
   public SelectableChannel getChannel() {
      return event.getChannel();
   }

   /**
    * This is used to acquire the Operation that is to
    * be executed when the required operations are ready. It is the
    * responsibility of the distributor to invoke the operation.
    * 
    * @return the operation to be executed when it is ready
    */
   public Operation getOperation() {
      return task;
   }
}