/*
    * 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.Channel;
  import io.netty5.channel.ChannelHandlerContext;
  import io.netty5.util.Resource;
  import io.netty5.util.concurrent.EventExecutor;
  import io.netty5.util.concurrent.EventExecutorGroup;
  import io.netty5.util.concurrent.Promise;
  
  import java.util.ArrayDeque;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.ConcurrentMap;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.atomic.AtomicLong;
  
  import static java.util.Objects.requireNonNull;
  
  /**
   * <p>This implementation of the {@link AbstractTrafficShapingHandler} is for global
   * traffic shaping, that is to say a global limitation of the bandwidth, whatever
   * the number of opened channels.</p>
   * <p>Note the index used in {@code OutboundBuffer.setUserDefinedWritability(index, boolean)} is <b>2</b>.</p>
   *
   * <p>The general use should be as follow:</p>
   * <ul>
   * <li><p>Create your unique GlobalTrafficShapingHandler like:</p>
   * <p><tt>GlobalTrafficShapingHandler myHandler = new GlobalTrafficShapingHandler(executor);</tt></p>
   * <p>The executor could be the underlying IO worker pool</p>
   * <p><tt>pipeline.addLast(myHandler);</tt></p>
   *
   * <p><b>Note that this handler has a Pipeline Coverage of "all" which means only one such handler must be created
   * and shared among all channels as the counter must 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>
   * So the expected usage of those methods are to be used not too often,
   * accordingly to the traffic shaping configuration.</li>
   * </ul>
   *
   * Be sure to call {@link #release()} once this handler is not needed anymore to release all internal resources.
   * This will not shutdown the {@link EventExecutor} as it may be shared, so you need to do this by your own.
   */
  public class GlobalTrafficShapingHandler extends AbstractTrafficShapingHandler {
      /**
       * All queues per channel
       */
      private final ConcurrentMap<Integer, PerChannel> channelQueues = new ConcurrentHashMap<>();
  
      /**
       * Global queues size
       */
      private final AtomicLong queuesSize = new AtomicLong();
  
      /**
       * Max size in the list before proposing to stop writing new objects from next handlers
       * for all channel (global)
       */
      long maxGlobalWriteSize = DEFAULT_MAX_SIZE * 100; // default 400MB
  
      private static final class PerChannel {
          ArrayDeque<ToSend> messagesQueue;
          long queueSize;
          long lastWriteTimestamp;
          long lastReadTimestamp;
     }
 
     /**
      * Create the global TrafficCounter.
      */
     void createGlobalTrafficCounter(EventExecutorGroup executor) {
         requireNonNull(executor, "executor");
         TrafficCounter tc = new TrafficCounter(this, executor, "GlobalTC", checkInterval);
         setTrafficCounter(tc);
         tc.start();
     }
 
     @Override
     public boolean isSharable() {
         return true;
     }
 
     @Override
     protected int userDefinedWritabilityIndex() {
         return AbstractTrafficShapingHandler.GLOBAL_DEFAULT_USER_DEFINED_WRITABILITY_INDEX;
     }
 
     /**
      * Create a new instance.
      *
      * @param executor
      *            the {@link EventExecutorGroup} to use for the {@link TrafficCounter}.
      * @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 GlobalTrafficShapingHandler(EventExecutorGroup executor, long writeLimit, long readLimit,
             long checkInterval, long maxTime) {
         super(writeLimit, readLimit, checkInterval, maxTime);
         createGlobalTrafficCounter(executor);
     }
 
     /**
      * Create a new instance using
      * default max time as delay allowed value of 15000 ms.
      *
      * @param executor
      *          the {@link EventExecutorGroup} to use for the {@link TrafficCounter}.
      * @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 GlobalTrafficShapingHandler(EventExecutorGroup executor, long writeLimit,
                                        long readLimit, long checkInterval) {
         super(writeLimit, readLimit, checkInterval);
         createGlobalTrafficCounter(executor);
     }
 
     /**
      * Create a new instance using default Check Interval value of 1000 ms and
      * default max time as delay allowed value of 15000 ms.
      *
      * @param executor
      *          the {@link EventExecutorGroup} to use for the {@link TrafficCounter}.
      * @param writeLimit
      *          0 or a limit in bytes/s
      * @param readLimit
      *          0 or a limit in bytes/s
      */
     public GlobalTrafficShapingHandler(EventExecutorGroup executor, long writeLimit,
             long readLimit) {
         super(writeLimit, readLimit);
         createGlobalTrafficCounter(executor);
     }
 
     /**
      * Create a new instance using
      * default max time as delay allowed value of 15000 ms and no limit.
      *
      * @param executor
      *          the {@link EventExecutorGroup} to use for the {@link TrafficCounter}.
      * @param checkInterval
      *          The delay between two computations of performances for
      *            channels or 0 if no stats are to be computed.
      */
     public GlobalTrafficShapingHandler(EventExecutorGroup executor, long checkInterval) {
         super(checkInterval);
         createGlobalTrafficCounter(executor);
     }
 
     /**
      * Create a new instance using default Check Interval value of 1000 ms and
      * default max time as delay allowed value of 15000 ms and no limit.
      *
      * @param executor
      *          the {@link EventExecutor} to use for the {@link TrafficCounter}.
      */
     public GlobalTrafficShapingHandler(EventExecutor executor) {
         createGlobalTrafficCounter(executor);
     }
 
     /**
      * @return the maxGlobalWriteSize default value being 400 MB.
      */
     public long getMaxGlobalWriteSize() {
         return maxGlobalWriteSize;
     }
 
     /**
      * Note the change will be taken as best effort, meaning
      * that all already scheduled traffics will not be
      * changed, but only applied to new traffics.<br>
      * So the expected usage of this method is to be used not too often,
      * accordingly to the traffic shaping configuration.
      *
      * @param maxGlobalWriteSize the maximum Global Write Size allowed in the buffer
      *            globally for all channels before write suspended is set,
      *            default value being 400 MB.
      */
     public void setMaxGlobalWriteSize(long maxGlobalWriteSize) {
         this.maxGlobalWriteSize = maxGlobalWriteSize;
     }
 
     /**
      * @return the global size of the buffers for all queues.
      */
     public long queuesSize() {
         return queuesSize.get();
     }
 
     /**
      * Release all internal resources of this instance.
      */
     public final void release() {
         trafficCounter.stop();
     }
 
     private PerChannel getOrSetPerChannel(ChannelHandlerContext ctx) {
         // ensure creation is limited to one thread per channel
         Channel channel = ctx.channel();
         Integer key = channel.hashCode();
         PerChannel perChannel = channelQueues.get(key);
         if (perChannel == null) {
             perChannel = new PerChannel();
             perChannel.messagesQueue = new ArrayDeque<>();
             perChannel.queueSize = 0L;
             perChannel.lastReadTimestamp = TrafficCounter.milliSecondFromNano();
             perChannel.lastWriteTimestamp = perChannel.lastReadTimestamp;
             channelQueues.put(key, perChannel);
         }
         return perChannel;
     }
 
     @Override
     public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
         getOrSetPerChannel(ctx);
         super.handlerAdded(ctx);
     }
 
     @Override
     public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
         Channel channel = ctx.channel();
         Integer key = channel.hashCode();
         PerChannel perChannel = channelQueues.remove(key);
         if (perChannel != null) {
             // write operations need synchronization
             synchronized (perChannel) {
                 if (channel.isActive()) {
                     for (ToSend toSend : perChannel.messagesQueue) {
                         long size = calculateSize(toSend.toSend);
                         trafficCounter.bytesRealWriteFlowControl(size);
                         perChannel.queueSize -= size;
                         queuesSize.addAndGet(-size);
                         ctx.write(toSend.toSend).cascadeTo(toSend.promise);
                     }
                 } else {
                     queuesSize.addAndGet(-perChannel.queueSize);
                     for (ToSend toSend : perChannel.messagesQueue) {
                         if (Resource.isAccessible(toSend.toSend, false)) {
                             Resource.dispose(toSend.toSend);
                         }
                     }
                 }
                 perChannel.messagesQueue.clear();
             }
         }
         releaseWriteSuspended(ctx);
         releaseReadSuspended(ctx);
         super.handlerRemoved(ctx);
     }
 
     @Override
     long checkWaitReadTime(final ChannelHandlerContext ctx, long wait, final long now) {
         Integer key = ctx.channel().hashCode();
         PerChannel perChannel = channelQueues.get(key);
         if (perChannel != null) {
             if (wait > maxTime && now + wait - perChannel.lastReadTimestamp > maxTime) {
                 wait = maxTime;
             }
         }
         return wait;
     }
 
     @Override
     void informReadOperation(final ChannelHandlerContext ctx, final long now) {
         Integer key = ctx.channel().hashCode();
         PerChannel perChannel = channelQueues.get(key);
         if (perChannel != null) {
             perChannel.lastReadTimestamp = now;
         }
     }
 
     private static final class ToSend {
         final long relativeTimeAction;
         final Object toSend;
         final long size;
         final Promise<Void> promise;
 
         private ToSend(final long delay, final Object toSend, final long size, final Promise<Void> promise) {
             relativeTimeAction = delay;
             this.toSend = toSend;
             this.size = size;
             this.promise = promise;
         }
     }
 
     @Override
     void submitWrite(final ChannelHandlerContext ctx, final Object msg,
             final long size, final long writedelay, final long now,
             final Promise<Void> promise) {
         Channel channel = ctx.channel();
         Integer key = channel.hashCode();
         PerChannel perChannel = channelQueues.get(key);
         if (perChannel == null) {
             // in case write occurs before handlerAdded is raised for this handler
             // imply a synchronized only if needed
             perChannel = getOrSetPerChannel(ctx);
         }
         final ToSend newToSend;
         long delay = writedelay;
         boolean globalSizeExceeded = false;
         // write operations need synchronization
         synchronized (perChannel) {
             if (writedelay == 0 && perChannel.messagesQueue.isEmpty()) {
                 trafficCounter.bytesRealWriteFlowControl(size);
                 ctx.write(msg).cascadeTo(promise);
                 perChannel.lastWriteTimestamp = now;
                 return;
             }
             if (delay > maxTime && now + delay - perChannel.lastWriteTimestamp > maxTime) {
                 delay = maxTime;
             }
             newToSend = new ToSend(delay + now, msg, size, promise);
             perChannel.messagesQueue.addLast(newToSend);
             perChannel.queueSize += size;
             queuesSize.addAndGet(size);
             checkWriteSuspend(ctx, delay, perChannel.queueSize);
             if (queuesSize.get() > maxGlobalWriteSize) {
                 globalSizeExceeded = true;
             }
         }
         if (globalSizeExceeded) {
             setUserDefinedWritability(ctx, false);
         }
         final long futureNow = newToSend.relativeTimeAction;
         final PerChannel forSchedule = perChannel;
         ctx.executor().schedule(() -> sendAllValid(ctx, forSchedule, futureNow), delay, TimeUnit.MILLISECONDS);
     }
 
     private void sendAllValid(final ChannelHandlerContext ctx, final PerChannel perChannel, final long now) {
         // write operations need synchronization
         synchronized (perChannel) {
             ToSend newToSend = perChannel.messagesQueue.pollFirst();
             for (; newToSend != null; newToSend = perChannel.messagesQueue.pollFirst()) {
                 if (newToSend.relativeTimeAction <= now) {
                     long size = newToSend.size;
                     trafficCounter.bytesRealWriteFlowControl(size);
                     perChannel.queueSize -= size;
                     queuesSize.addAndGet(-size);
                     ctx.write(newToSend.toSend).cascadeTo(newToSend.promise);
                     perChannel.lastWriteTimestamp = now;
                 } else {
                     perChannel.messagesQueue.addFirst(newToSend);
                     break;
                 }
             }
             if (perChannel.messagesQueue.isEmpty()) {
                 releaseWriteSuspended(ctx);
             }
         }
         ctx.flush();
     }
 }