/*
    *  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.mina.filter.executor;
  
  import java.util.concurrent.atomic.AtomicInteger;
  
  import org.apache.mina.core.session.IoEvent;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * Throttles incoming or outgoing events.
   *
   * @author <a href="http://mina.apache.org">Apache MINA Project</a>
   */
  public class IoEventQueueThrottle implements IoEventQueueHandler {
      /** A logger for this class */
      private static final Logger LOGGER = LoggerFactory.getLogger(IoEventQueueThrottle.class);
  
      /** The event size estimator instance */
      private final IoEventSizeEstimator eventSizeEstimator;
  
      private volatile int threshold;
  
      private final Object lock = new Object();
  
      /** The number of events we hold */
      private final AtomicInteger counter = new AtomicInteger();
  
      private int waiters;
  
      /**
       * Creates a new IoEventQueueThrottle instance
       */
      public IoEventQueueThrottle() {
          this(new DefaultIoEventSizeEstimator(), 65536);
      }
  
      /**
       * Creates a new IoEventQueueThrottle instance
       * 
       * @param threshold The events threshold
       */
      public IoEventQueueThrottle(int threshold) {
          this(new DefaultIoEventSizeEstimator(), threshold);
      }
  
      /**
       * Creates a new IoEventQueueThrottle instance
       *
       * @param eventSizeEstimator The IoEventSizeEstimator instance
       * @param threshold The events threshold
       */
      public IoEventQueueThrottle(IoEventSizeEstimator eventSizeEstimator, int threshold) {
          if (eventSizeEstimator == null) {
              throw new IllegalArgumentException("eventSizeEstimator");
          }
          
          this.eventSizeEstimator = eventSizeEstimator;
  
          setThreshold(threshold);
      }
  
      /**
       * @return The IoEventSizeEstimator instance
       */
      public IoEventSizeEstimator getEventSizeEstimator() {
          return eventSizeEstimator;
      }
  
      /**
       * @return The events threshold
       */
      public int getThreshold() {
          return threshold;
      }
  
      /**
       * @return The number of events currently held
       */
      public int getCounter() {
          return counter.get();
     }
 
     /**
      * Sets the events threshold
      * 
      * @param threshold The events threshold
      */
     public void setThreshold(int threshold) {
         if (threshold <= 0) {
             throw new IllegalArgumentException("threshold: " + threshold);
         }
         
         this.threshold = threshold;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public boolean accept(Object source, IoEvent event) {
         return true;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public void offered(Object source, IoEvent event) {
         int eventSize = estimateSize(event);
         int currentCounter = counter.addAndGet(eventSize);
         logState();
 
         if (currentCounter >= threshold) {
             block();
         }
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public void polled(Object source, IoEvent event) {
         int eventSize = estimateSize(event);
         int currentCounter = counter.addAndGet(-eventSize);
 
         logState();
 
         if (currentCounter < threshold) {
             unblock();
         }
     }
 
     private int estimateSize(IoEvent event) {
         int size = getEventSizeEstimator().estimateSize(event);
         
         if (size < 0) {
             throw new IllegalStateException(IoEventSizeEstimator.class.getSimpleName() + " returned "
                     + "a negative value (" + size + "): " + event);
         }
         
         return size;
     }
 
     private void logState() {
         if (LOGGER.isDebugEnabled()) {
             LOGGER.debug(Thread.currentThread().getName() + " state: " + counter.get() + " / " + getThreshold());
         }
     }
 
     protected void block() {
         if (LOGGER.isDebugEnabled()) {
             LOGGER.debug(Thread.currentThread().getName() + " blocked: " + counter.get() + " >= " + threshold);
         }
 
         synchronized (lock) {
             while (counter.get() >= threshold) {
                 waiters++;
                 try {
                     lock.wait();
                 } catch (InterruptedException e) {
                     // Wait uninterruptably.
                 } finally {
                     waiters--;
                 }
             }
         }
 
         if (LOGGER.isDebugEnabled()) {
             LOGGER.debug(Thread.currentThread().getName() + " unblocked: " + counter.get() + " < " + threshold);
         }
     }
 
     protected void unblock() {
         synchronized (lock) {
             if (waiters > 0) {
                 lock.notifyAll();
             }
         }
     }
 }