/*
    * Copyright 2012 The Netty Project
    *
    * The Netty Project 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:
    *
    * https://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 io.netty5.handler.traffic;
  
  import io.netty5.channel.ChannelHandlerContext;
  import io.netty5.util.Resource;
  import io.netty5.util.concurrent.Promise;
  
  import java.util.ArrayDeque;
  import java.util.concurrent.TimeUnit;
  
  /**
   * <p>This implementation of the {@link AbstractTrafficShapingHandler} is for channel
   * traffic shaping, that is to say a per channel limitation of the bandwidth.</p>
   * <p>Note the index used in {@code OutboundBuffer.setUserDefinedWritability(index, boolean)} is <b>1</b>.</p>
   *
   * <p>The general use should be as follow:</p>
   * <ul>
   * <li><p>Add in your pipeline a new ChannelTrafficShapingHandler.</p>
   * <p><tt>ChannelTrafficShapingHandler myHandler = new ChannelTrafficShapingHandler();</tt></p>
   * <p><tt>pipeline.addLast(myHandler);</tt></p>
   *
   * <p><b>Note that this handler has a Pipeline Coverage of "one" which means a new handler must be created
   * for each new channel as the counter cannot be shared among all channels.</b>.</p>
   *
   * <p>Other arguments can be passed like write or read limitation (in bytes/s where 0 means no limitation)
   * or the check interval (in millisecond) that represents the delay between two computations of the
   * bandwidth and so the call back of the doAccounting method (0 means no accounting at all).</p>
   *
   * <p>A value of 0 means no accounting for checkInterval. If you need traffic shaping but no such accounting,
   * it is recommended to set a positive value, even if it is high since the precision of the
   * Traffic Shaping depends on the period where the traffic is computed. The highest the interval,
   * the less precise the traffic shaping will be. It is suggested as higher value something close
   * to 5 or 10 minutes.</p>
   *
   * <p>maxTimeToWait, by default set to 15s, allows to specify an upper bound of time shaping.</p>
   * </li>
   * <li>In your handler, you should consider to use the {@code channel.isWritable()} and
   * {@code channelWritabilityChanged(ctx)} to handle writability, or through
   * {@code future.addListener(future -> ...)} on the future returned by
   * {@code ctx.write()}.</li>
   * <li><p>You shall also consider to have object size in read or write operations relatively adapted to
   * the bandwidth you required: for instance having 10 MB objects for 10KB/s will lead to burst effect,
   * while having 100 KB objects for 1 MB/s should be smoothly handle by this TrafficShaping handler.</p></li>
   * <li><p>Some configuration methods will be taken as best effort, meaning
   * that all already scheduled traffics will not be
   * changed, but only applied to new traffics.</p>
   * <p>So the expected usage of those methods are to be used not too often,
   * accordingly to the traffic shaping configuration.</p></li>
   * </ul>
   */
  public class ChannelTrafficShapingHandler extends AbstractTrafficShapingHandler {
      private final ArrayDeque<ToSend> messagesQueue = new ArrayDeque<>();
      private long queueSize;
  
      /**
       * Create a new instance.
       *
       * @param writeLimit
       *            0 or a limit in bytes/s
       * @param readLimit
       *            0 or a limit in bytes/s
       * @param checkInterval
       *            The delay between two computations of performances for
       *            channels or 0 if no stats are to be computed.
       * @param maxTime
       *            The maximum delay to wait in case of traffic excess.
       */
      public ChannelTrafficShapingHandler(long writeLimit, long readLimit,
              long checkInterval, long maxTime) {
          super(writeLimit, readLimit, checkInterval, maxTime);
      }
  
      /**
       * Create a new instance using default
       * max time as delay allowed value of 15000 ms.
       *
       * @param writeLimit
       *          0 or a limit in bytes/s
       * @param readLimit
       *          0 or a limit in bytes/s
       * @param checkInterval
       *          The delay between two computations of performances for
       *            channels or 0 if no stats are to be computed.
       */
      public ChannelTrafficShapingHandler(long writeLimit,
             long readLimit, long checkInterval) {
         super(writeLimit, readLimit, checkInterval);
     }
 
     /**
      * Create a new instance using default Check Interval value of 1000 ms and
      * max time as delay allowed value of 15000 ms.
      *
      * @param writeLimit
      *          0 or a limit in bytes/s
      * @param readLimit
      *          0 or a limit in bytes/s
      */
     public ChannelTrafficShapingHandler(long writeLimit,
             long readLimit) {
         super(writeLimit, readLimit);
     }
 
     /**
      * Create a new instance using
      * default max time as delay allowed value of 15000 ms and no limit.
      *
      * @param checkInterval
      *          The delay between two computations of performances for
      *            channels or 0 if no stats are to be computed.
      */
     public ChannelTrafficShapingHandler(long checkInterval) {
         super(checkInterval);
     }
 
     @Override
     public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
         TrafficCounter trafficCounter = new TrafficCounter(this, ctx.executor(), "ChannelTC" +
                 ctx.channel().hashCode(), checkInterval);
         setTrafficCounter(trafficCounter);
         trafficCounter.start();
         super.handlerAdded(ctx);
     }
 
     @Override
     public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
         trafficCounter.stop();
         // write order control
         synchronized (this) {
             if (ctx.channel().isActive()) {
                 for (ToSend toSend : messagesQueue) {
                     long size = calculateSize(toSend.toSend);
                     trafficCounter.bytesRealWriteFlowControl(size);
                     queueSize -= size;
                     ctx.write(toSend.toSend).cascadeTo(toSend.promise);
                 }
             } else {
                 for (ToSend toSend : messagesQueue) {
                     if (Resource.isAccessible(toSend.toSend, false)) {
                         Resource.dispose(toSend.toSend);
                     }
                 }
             }
             messagesQueue.clear();
         }
         releaseWriteSuspended(ctx);
         releaseReadSuspended(ctx);
         super.handlerRemoved(ctx);
     }
 
     private static final class ToSend {
         final long relativeTimeAction;
         final Object toSend;
         final Promise<Void> promise;
 
         private ToSend(final long delay, final Object toSend, final Promise<Void> promise) {
             relativeTimeAction = delay;
             this.toSend = toSend;
             this.promise = promise;
         }
     }
 
     @Override
     void submitWrite(final ChannelHandlerContext ctx, final Object msg,
             final long size, final long delay, final long now,
             final Promise<Void> promise) {
         final ToSend newToSend;
         // write order control
         synchronized (this) {
             if (delay == 0 && messagesQueue.isEmpty()) {
                 trafficCounter.bytesRealWriteFlowControl(size);
                 ctx.write(msg).cascadeTo(promise);
                 return;
             }
             newToSend = new ToSend(delay + now, msg, promise);
             messagesQueue.addLast(newToSend);
             queueSize += size;
             checkWriteSuspend(ctx, delay, queueSize);
         }
         final long futureNow = newToSend.relativeTimeAction;
         ctx.executor().schedule(() -> sendAllValid(ctx, futureNow), delay, TimeUnit.MILLISECONDS);
     }
 
     private void sendAllValid(final ChannelHandlerContext ctx, final long now) {
         // write order control
         synchronized (this) {
             ToSend newToSend = messagesQueue.pollFirst();
             for (; newToSend != null; newToSend = messagesQueue.pollFirst()) {
                 if (newToSend.relativeTimeAction <= now) {
                     long size = calculateSize(newToSend.toSend);
                     trafficCounter.bytesRealWriteFlowControl(size);
                     queueSize -= size;
                     ctx.write(newToSend.toSend).cascadeTo(newToSend.promise);
                 } else {
                     messagesQueue.addFirst(newToSend);
                     break;
                 }
             }
             if (messagesQueue.isEmpty()) {
                 releaseWriteSuspended(ctx);
             }
         }
         ctx.flush();
     }
 
     /**
     * @return current size in bytes of the write buffer.
     */
    public long queueSize() {
        return queueSize;
    }
 }