/*
    * Copyright 2016 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.netty.handler.codec.http2;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.channel.Channel;
  import io.netty.channel.ChannelConfig;
  import io.netty.channel.ChannelFuture;
  import io.netty.channel.ChannelHandler;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.ChannelPromise;
  import io.netty.channel.EventLoop;
  import io.netty.util.ReferenceCounted;
  
  import io.netty.util.internal.UnstableApi;
  
  import java.util.ArrayDeque;
  import java.util.Queue;
  
  import static io.netty.handler.codec.http2.Http2CodecUtil.HTTP_UPGRADE_STREAM_ID;
  import static io.netty.handler.codec.http2.Http2Error.INTERNAL_ERROR;
  import static io.netty.handler.codec.http2.Http2Exception.connectionError;
  
  /**
   * An HTTP/2 handler that creates child channels for each stream.
   *
   * <p>When a new stream is created, a new {@link Channel} is created for it. Applications send and
   * receive {@link Http2StreamFrame}s on the created channel. {@link ByteBuf}s cannot be processed by the channel;
   * all writes that reach the head of the pipeline must be an instance of {@link Http2StreamFrame}. Writes that reach
   * the head of the pipeline are processed directly by this handler and cannot be intercepted.
   *
   * <p>The child channel will be notified of user events that impact the stream, such as {@link
   * Http2GoAwayFrame} and {@link Http2ResetFrame}, as soon as they occur. Although {@code
   * Http2GoAwayFrame} and {@code Http2ResetFrame} signify that the remote is ignoring further
   * communication, closing of the channel is delayed until any inbound queue is drained with {@link
   * Channel#read()}, which follows the default behavior of channels in Netty. Applications are
   * free to close the channel in response to such events if they don't have use for any queued
   * messages. Any connection level events like {@link Http2SettingsFrame} and {@link Http2GoAwayFrame}
   * will be processed internally and also propagated down the pipeline for other handlers to act on.
   *
   * <p>Outbound streams are supported via the {@link Http2StreamChannelBootstrap}.
   *
   * <p>{@link ChannelConfig#setMaxMessagesPerRead(int)} and {@link ChannelConfig#setAutoRead(boolean)} are supported.
   *
   * <h3>Reference Counting</h3>
   *
   * Some {@link Http2StreamFrame}s implement the {@link ReferenceCounted} interface, as they carry
   * reference counted objects (e.g. {@link ByteBuf}s). The multiplex codec will call {@link ReferenceCounted#retain()}
   * before propagating a reference counted object through the pipeline, and thus an application handler needs to release
   * such an object after having consumed it. For more information on reference counting take a look at
   * https://netty.io/wiki/reference-counted-objects.html
   *
   * <h3>Channel Events</h3>
   *
   * A child channel becomes active as soon as it is registered to an {@link EventLoop}. Therefore, an active channel
   * does not map to an active HTTP/2 stream immediately. Only once a {@link Http2HeadersFrame} has been successfully sent
   * or received, does the channel map to an active HTTP/2 stream. In case it is not possible to open a new HTTP/2 stream
   * (i.e. due to the maximum number of active streams being exceeded), the child channel receives an exception
   * indicating the cause and is closed immediately thereafter.
   *
   * <h3>Writability and Flow Control</h3>
   *
   * A child channel observes outbound/remote flow control via the channel's writability. A channel only becomes writable
   * when it maps to an active HTTP/2 stream and the stream's flow control window is greater than zero. A child channel
   * does not know about the connection-level flow control window. {@link ChannelHandler}s are free to ignore the
   * channel's writability, in which case the excessive writes will be buffered by the parent channel. It's important to
   * note that only {@link Http2DataFrame}s are subject to HTTP/2 flow control.
   *
   * @deprecated use {@link Http2FrameCodecBuilder} together with {@link Http2MultiplexHandler}.
   */
  @Deprecated
  @UnstableApi
  public class Http2MultiplexCodec extends Http2FrameCodec {
  
      private final ChannelHandler inboundStreamHandler;
      private final ChannelHandler upgradeStreamHandler;
      private final Queue<AbstractHttp2StreamChannel> readCompletePendingQueue =
              new MaxCapacityQueue<AbstractHttp2StreamChannel>(new ArrayDeque<AbstractHttp2StreamChannel>(8),
                      // Choose 100 which is what is used most of the times as default.
                      Http2CodecUtil.SMALLEST_MAX_CONCURRENT_STREAMS);
  
      private boolean parentReadInProgress;
      private int idCount;
  
      // Need to be volatile as accessed from within the Http2MultiplexCodecStreamChannel in a multi-threaded fashion.
      volatile ChannelHandlerContext ctx;
 
     Http2MultiplexCodec(Http2ConnectionEncoder encoder,
                         Http2ConnectionDecoder decoder,
                         Http2Settings initialSettings,
                         ChannelHandler inboundStreamHandler,
                         ChannelHandler upgradeStreamHandler, boolean decoupleCloseAndGoAway, boolean flushPreface) {
         super(encoder, decoder, initialSettings, decoupleCloseAndGoAway, flushPreface);
         this.inboundStreamHandler = inboundStreamHandler;
         this.upgradeStreamHandler = upgradeStreamHandler;
     }
 
     @Override
     public void onHttpClientUpgrade() throws Http2Exception {
         // We must have an upgrade handler or else we can't handle the stream
         if (upgradeStreamHandler == null) {
             throw connectionError(INTERNAL_ERROR, "Client is misconfigured for upgrade requests");
         }
         // Creates the Http2Stream in the Connection.
         super.onHttpClientUpgrade();
     }
 
     @Override
     public final void handlerAdded0(ChannelHandlerContext ctx) throws Exception {
         if (ctx.executor() != ctx.channel().eventLoop()) {
             throw new IllegalStateException("EventExecutor must be EventLoop of Channel");
         }
         this.ctx = ctx;
     }
 
     @Override
     public final void handlerRemoved0(ChannelHandlerContext ctx) throws Exception {
         super.handlerRemoved0(ctx);
 
         readCompletePendingQueue.clear();
     }
 
     @Override
     final void onHttp2Frame(ChannelHandlerContext ctx, Http2Frame frame) {
         if (frame instanceof Http2StreamFrame) {
             Http2StreamFrame streamFrame = (Http2StreamFrame) frame;
             AbstractHttp2StreamChannel channel  = (AbstractHttp2StreamChannel)
                     ((DefaultHttp2FrameStream) streamFrame.stream()).attachment;
             channel.fireChildRead(streamFrame);
             return;
         }
         if (frame instanceof Http2GoAwayFrame) {
             onHttp2GoAwayFrame(ctx, (Http2GoAwayFrame) frame);
         }
         // Send frames down the pipeline
         ctx.fireChannelRead(frame);
     }
 
     @Override
     final void onHttp2StreamStateChanged(ChannelHandlerContext ctx, DefaultHttp2FrameStream stream) {
         switch (stream.state()) {
             case HALF_CLOSED_LOCAL:
                 if (stream.id() != HTTP_UPGRADE_STREAM_ID) {
                     // Ignore everything which was not caused by an upgrade
                     break;
                 }
                 // fall-through
             case HALF_CLOSED_REMOTE:
                 // fall-through
             case OPEN:
                 if (stream.attachment != null) {
                     // ignore if child channel was already created.
                     break;
                 }
                 final Http2MultiplexCodecStreamChannel streamChannel;
                 // We need to handle upgrades special when on the client side.
                 if (stream.id() == HTTP_UPGRADE_STREAM_ID && !connection().isServer()) {
                     // Add our upgrade handler to the channel and then register the channel.
                     // The register call fires the channelActive, etc.
                     assert upgradeStreamHandler != null;
                     streamChannel = new Http2MultiplexCodecStreamChannel(stream, upgradeStreamHandler);
                     streamChannel.closeOutbound();
                 } else {
                     streamChannel = new Http2MultiplexCodecStreamChannel(stream, inboundStreamHandler);
                 }
                 ChannelFuture future = ctx.channel().eventLoop().register(streamChannel);
                 if (future.isDone()) {
                     Http2MultiplexHandler.registerDone(future);
                 } else {
                     future.addListener(Http2MultiplexHandler.CHILD_CHANNEL_REGISTRATION_LISTENER);
                 }
                 break;
             case CLOSED:
                 AbstractHttp2StreamChannel channel = (AbstractHttp2StreamChannel) stream.attachment;
                 if (channel != null) {
                     channel.streamClosed();
                 }
                 break;
             default:
                 // ignore for now
                 break;
         }
     }
 
     // TODO: This is most likely not the best way to expose this, need to think more about it.
     final Http2StreamChannel newOutboundStream() {
         return new Http2MultiplexCodecStreamChannel(newStream(), null);
     }
 
     @Override
     final void onHttp2FrameStreamException(ChannelHandlerContext ctx, Http2FrameStreamException cause) {
         Http2FrameStream stream = cause.stream();
         AbstractHttp2StreamChannel channel = (AbstractHttp2StreamChannel) ((DefaultHttp2FrameStream) stream).attachment;
 
         try {
             channel.pipeline().fireExceptionCaught(cause.getCause());
         } finally {
             channel.unsafe().closeForcibly();
         }
     }
 
     private void onHttp2GoAwayFrame(ChannelHandlerContext ctx, final Http2GoAwayFrame goAwayFrame) {
         if (goAwayFrame.lastStreamId() == Integer.MAX_VALUE) {
             // None of the streams can have an id greater than Integer.MAX_VALUE
             return;
         }
         // Notify which streams were not processed by the remote peer and are safe to retry on another connection:
         try {
             forEachActiveStream(new Http2FrameStreamVisitor() {
                 @Override
                 public boolean visit(Http2FrameStream stream) {
                     final int streamId = stream.id();
                     AbstractHttp2StreamChannel channel = (AbstractHttp2StreamChannel)
                             ((DefaultHttp2FrameStream) stream).attachment;
                     if (streamId > goAwayFrame.lastStreamId() && connection().local().isValidStreamId(streamId)) {
                         channel.pipeline().fireUserEventTriggered(goAwayFrame.retainedDuplicate());
                     }
                     return true;
                 }
             });
         } catch (Http2Exception e) {
             ctx.fireExceptionCaught(e);
             ctx.close();
         }
     }
 
     /**
      * Notifies any child streams of the read completion.
      */
     @Override
     public final void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
         processPendingReadCompleteQueue();
         channelReadComplete0(ctx);
     }
 
     private void processPendingReadCompleteQueue() {
         parentReadInProgress = true;
         try {
             // If we have many child channel we can optimize for the case when multiple call flush() in
             // channelReadComplete(...) callbacks and only do it once as otherwise we will end-up with multiple
             // write calls on the socket which is expensive.
             for (;;) {
                 AbstractHttp2StreamChannel childChannel = readCompletePendingQueue.poll();
                 if (childChannel == null) {
                     break;
                 }
                 childChannel.fireChildReadComplete();
             }
         } finally {
             parentReadInProgress = false;
             readCompletePendingQueue.clear();
             // We always flush as this is what Http2ConnectionHandler does for now.
             flush0(ctx);
         }
     }
     @Override
     public final void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
         parentReadInProgress = true;
         super.channelRead(ctx, msg);
     }
 
     @Override
     public final void channelWritabilityChanged(final ChannelHandlerContext ctx) throws Exception {
         if (ctx.channel().isWritable()) {
             // While the writability state may change during iterating of the streams we just set all of the streams
             // to writable to not affect fairness. These will be "limited" by their own watermarks in any case.
             forEachActiveStream(AbstractHttp2StreamChannel.WRITABLE_VISITOR);
         }
 
         super.channelWritabilityChanged(ctx);
     }
 
     final void flush0(ChannelHandlerContext ctx) {
         flush(ctx);
     }
 
     private final class Http2MultiplexCodecStreamChannel extends AbstractHttp2StreamChannel {
 
         Http2MultiplexCodecStreamChannel(DefaultHttp2FrameStream stream, ChannelHandler inboundHandler) {
             super(stream, ++idCount, inboundHandler);
         }
 
         @Override
         protected boolean isParentReadInProgress() {
             return parentReadInProgress;
         }
 
         @Override
         protected void addChannelToReadCompletePendingQueue() {
             // If there is no space left in the queue, just keep on processing everything that is already
             // stored there and try again.
             while (!readCompletePendingQueue.offer(this)) {
                 processPendingReadCompleteQueue();
             }
         }
 
         @Override
         protected ChannelHandlerContext parentContext() {
             return ctx;
         }
 
         @Override
         protected ChannelFuture write0(ChannelHandlerContext ctx, Object msg) {
             ChannelPromise promise = ctx.newPromise();
             Http2MultiplexCodec.this.write(ctx, msg, promise);
             return promise;
         }
 
         @Override
         protected void flush0(ChannelHandlerContext ctx) {
             Http2MultiplexCodec.this.flush0(ctx);
         }
     }
 }