/*
    * Copyright 2014 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.codec.http2;
  
  import io.netty5.buffer.api.Buffer;
  import io.netty5.channel.ChannelHandlerContext;
  import io.netty5.channel.embedded.EmbeddedChannel;
  import io.netty5.handler.codec.compression.Brotli;
  import io.netty5.handler.codec.compression.BrotliDecompressor;
  import io.netty5.handler.codec.compression.Decompressor;
  import io.netty5.handler.codec.compression.ZlibDecompressor;
  import io.netty5.handler.codec.compression.ZlibWrapper;
  import io.netty5.util.internal.UnstableApi;
  
  import static io.netty5.handler.codec.http.HttpHeaderNames.CONTENT_ENCODING;
  import static io.netty5.handler.codec.http.HttpHeaderNames.CONTENT_LENGTH;
  import static io.netty5.handler.codec.http.HttpHeaderValues.BR;
  import static io.netty5.handler.codec.http.HttpHeaderValues.DEFLATE;
  import static io.netty5.handler.codec.http.HttpHeaderValues.GZIP;
  import static io.netty5.handler.codec.http.HttpHeaderValues.IDENTITY;
  import static io.netty5.handler.codec.http.HttpHeaderValues.X_DEFLATE;
  import static io.netty5.handler.codec.http.HttpHeaderValues.X_GZIP;
  import static io.netty5.handler.codec.http2.Http2Error.INTERNAL_ERROR;
  import static io.netty5.handler.codec.http2.Http2Exception.streamError;
  import static io.netty5.util.internal.ObjectUtil.checkPositiveOrZero;
  import static java.util.Objects.requireNonNull;
  
  /**
   * An HTTP2 frame listener that will decompress data frames according to the {@code content-encoding} header for each
   * stream. The decompression provided by this class will be applied to the data for the entire stream.
   */
  @UnstableApi
  public class DelegatingDecompressorFrameListener extends Http2FrameListenerDecorator {
  
      private final Http2Connection connection;
      private final boolean strict;
      private boolean flowControllerInitialized;
      private final Http2Connection.PropertyKey propertyKey;
  
      public DelegatingDecompressorFrameListener(Http2Connection connection, Http2FrameListener listener) {
          this(connection, listener, true);
      }
  
      public DelegatingDecompressorFrameListener(Http2Connection connection, Http2FrameListener listener,
                      boolean strict) {
          super(listener);
          this.connection = connection;
          this.strict = strict;
  
          propertyKey = connection.newKey();
          connection.addListener(new Http2ConnectionAdapter() {
              @Override
              public void onStreamRemoved(Http2Stream stream) {
                  final Http2Decompressor decompressor = decompressor(stream);
                  if (decompressor != null) {
                      cleanup(decompressor);
                  }
              }
          });
      }
  
      @Override
      public int onDataRead(ChannelHandlerContext ctx, int streamId, Buffer data, int padding, boolean endOfStream)
              throws Http2Exception {
          final Http2Stream stream = connection.stream(streamId);
          final Http2Decompressor decompressor = decompressor(stream);
          if (decompressor == null) {
              // The decompressor may be null if no compatible encoding type was found in this stream's headers
              return listener.onDataRead(ctx, streamId, data, padding, endOfStream);
          }
  
          final Decompressor decomp = decompressor.decompressor();
          final int compressedBytes = data.readableBytes() + padding;
          decompressor.incrementCompressedBytes(compressedBytes);
          Buffer decompressed = null;
          try {
              Http2LocalFlowController flowController = connection.local().flowController();
              decompressor.incrementDecompressedBytes(padding);
  
              for (;;) {
                  if (decomp.isFinished()) {
                      flowController.consumeBytes(stream, listener.onDataRead(
                              ctx, streamId, ctx.bufferAllocator().allocate(0), padding, endOfStream));
                      break;
                  }
                  int idx = data.readerOffset();
                  decompressed = decomp.decompress(data, ctx.bufferAllocator());
                 if (decompressed == null || idx == data.readerOffset()) {
                     flowController.consumeBytes(stream, listener.onDataRead(
                             ctx, streamId, ctx.bufferAllocator().allocate(0), padding, endOfStream));
                     break;
                 } else {
                     // Immediately return the bytes back to the flow controller. ConsumedBytesConverter will convert
                     // from the decompressed amount which the user knows about to the compressed amount which flow
                     // control knows about.
                     decompressor.incrementDecompressedBytes(decompressed.readableBytes());
                     flowController.consumeBytes(stream,
                             listener.onDataRead(ctx, streamId, decompressed, padding, false));
                     decompressed.close();
                     decompressed = null;
                 }
                 padding = 0; // Padding is only communicated once on the first iteration.
             }
             // We consume bytes each time we call the listener to ensure if multiple frames are decompressed
             // that the bytes are accounted for immediately. Otherwise the user may see an inconsistent state of
             // flow control.
             return 0;
         } catch (Http2Exception e) {
             throw e;
         } catch (Throwable t) {
             throw streamError(stream.id(), INTERNAL_ERROR, t,
                     "Decompressor error detected while delegating data read on streamId %d", stream.id());
         } finally {
             if (decompressed != null) {
                 decompressed.close();
             }
         }
     }
 
     @Override
     public void onHeadersRead(ChannelHandlerContext ctx, int streamId, Http2Headers headers, int padding,
                     boolean endStream) throws Http2Exception {
         initDecompressor(ctx, streamId, headers, endStream);
         listener.onHeadersRead(ctx, streamId, headers, padding, endStream);
     }
 
     @Override
     public void onHeadersRead(ChannelHandlerContext ctx, int streamId, Http2Headers headers, int streamDependency,
                     short weight, boolean exclusive, int padding, boolean endStream) throws Http2Exception {
         initDecompressor(ctx, streamId, headers, endStream);
         listener.onHeadersRead(ctx, streamId, headers, streamDependency, weight, exclusive, padding, endStream);
     }
 
     /**
      * Returns a new {@link EmbeddedChannel} that decodes the HTTP2 message content encoded in the specified
      * {@code contentEncoding}.
      *
      * @param contentEncoding the value of the {@code content-encoding} header
      * @return a new {@link Decompressor} if the specified encoding is supported. {@code null} otherwise
      *         (alternatively, you can throw a {@link Http2Exception} to block unknown encoding).
      * @throws Http2Exception If the specified encoding is not supported and warrants an exception
      */
     protected Decompressor newContentDecompressor(final ChannelHandlerContext ctx, CharSequence contentEncoding)
             throws Http2Exception {
         if (GZIP.contentEqualsIgnoreCase(contentEncoding) || X_GZIP.contentEqualsIgnoreCase(contentEncoding)) {
             return ZlibDecompressor.newFactory(ZlibWrapper.GZIP).get();
         }
         if (DEFLATE.contentEqualsIgnoreCase(contentEncoding) || X_DEFLATE.contentEqualsIgnoreCase(contentEncoding)) {
             final ZlibWrapper wrapper = strict ? ZlibWrapper.ZLIB : ZlibWrapper.ZLIB_OR_NONE;
             // To be strict, 'deflate' means ZLIB, but some servers were not implemented correctly.
             return ZlibDecompressor.newFactory(wrapper).get();
         }
         if (Brotli.isAvailable() && BR.contentEqualsIgnoreCase(contentEncoding)) {
             return BrotliDecompressor.newFactory().get();
         }
         // 'identity' or unsupported
         return null;
     }
 
     /**
      * Returns the expected content encoding of the decoded content. This getMethod returns {@code "identity"} by
      * default, which is the case for most decompressors.
      *
      * @param contentEncoding the value of the {@code content-encoding} header
      * @return the expected content encoding of the new content.
      * @throws Http2Exception if the {@code contentEncoding} is not supported and warrants an exception
      */
     protected CharSequence getTargetContentEncoding(@SuppressWarnings("UnusedParameters") CharSequence contentEncoding)
                     throws Http2Exception {
         return IDENTITY;
     }
 
     /**
      * Checks if a new decompressor object is needed for the stream identified by {@code streamId}.
      * This method will modify the {@code content-encoding} header contained in {@code headers}.
      *
      * @param ctx The context
      * @param streamId The identifier for the headers inside {@code headers}
      * @param headers Object representing headers which have been read
      * @param endOfStream Indicates if the stream has ended
      * @throws Http2Exception If the {@code content-encoding} is not supported
      */
     private void initDecompressor(ChannelHandlerContext ctx, int streamId, Http2Headers headers, boolean endOfStream)
             throws Http2Exception {
         final Http2Stream stream = connection.stream(streamId);
         if (stream == null) {
             return;
         }
 
         Http2Decompressor decompressor = decompressor(stream);
         if (decompressor == null && !endOfStream) {
             // Determine the content encoding.
             CharSequence contentEncoding = headers.get(CONTENT_ENCODING);
             if (contentEncoding == null) {
                 contentEncoding = IDENTITY;
             }
             final Decompressor decomp = newContentDecompressor(ctx, contentEncoding);
             if (decomp != null) {
                 decompressor = new Http2Decompressor(decomp);
                 stream.setProperty(propertyKey, decompressor);
                 // Decode the content and remove or replace the existing headers
                 // so that the message looks like a decoded message.
                 CharSequence targetContentEncoding = getTargetContentEncoding(contentEncoding);
                 if (IDENTITY.contentEqualsIgnoreCase(targetContentEncoding)) {
                     headers.remove(CONTENT_ENCODING);
                 } else {
                     headers.set(CONTENT_ENCODING, targetContentEncoding);
                 }
             }
         }
 
         if (decompressor != null) {
             // The content length will be for the compressed data. Since we will decompress the data
             // this content-length will not be correct. Instead of queuing messages or delaying sending
             // header frames just remove the content-length header.
             headers.remove(CONTENT_LENGTH);
 
             // The first time that we initialize a decompressor, decorate the local flow controller to
             // properly convert consumed bytes.
             if (!flowControllerInitialized) {
                 flowControllerInitialized = true;
                 connection.local().flowController(new ConsumedBytesConverter(connection.local().flowController()));
             }
         }
     }
 
     Http2Decompressor decompressor(Http2Stream stream) {
         return stream == null ? null : (Http2Decompressor) stream.getProperty(propertyKey);
     }
 
     /**
      * Release remaining content from the {@link Decompressor}.
      *
      * @param decompressor The decompressor for {@code stream}
      */
     private static void cleanup(Http2Decompressor decompressor) {
         decompressor.decompressor().close();
     }
 
     /**
      * A decorator around the local flow controller that converts consumed bytes from uncompressed to compressed.
      */
     private final class ConsumedBytesConverter implements Http2LocalFlowController {
         private final Http2LocalFlowController flowController;
 
         ConsumedBytesConverter(Http2LocalFlowController flowController) {
             this.flowController = requireNonNull(flowController, "flowController");
         }
 
         @Override
         public Http2LocalFlowController frameWriter(Http2FrameWriter frameWriter) {
             return flowController.frameWriter(frameWriter);
         }
 
         @Override
         public void channelHandlerContext(ChannelHandlerContext ctx) throws Http2Exception {
             flowController.channelHandlerContext(ctx);
         }
 
         @Override
         public void initialWindowSize(int newWindowSize) throws Http2Exception {
             flowController.initialWindowSize(newWindowSize);
         }
 
         @Override
         public int initialWindowSize() {
             return flowController.initialWindowSize();
         }
 
         @Override
         public int windowSize(Http2Stream stream) {
             return flowController.windowSize(stream);
         }
 
         @Override
         public void incrementWindowSize(Http2Stream stream, int delta) throws Http2Exception {
             flowController.incrementWindowSize(stream, delta);
         }
 
         @Override
         public void receiveFlowControlledFrame(Http2Stream stream, Buffer data, int padding,
                                                boolean endOfStream) throws Http2Exception {
             flowController.receiveFlowControlledFrame(stream, data, padding, endOfStream);
         }
 
         @Override
         public boolean consumeBytes(Http2Stream stream, int numBytes) throws Http2Exception {
             Http2Decompressor decompressor = decompressor(stream);
             if (decompressor != null) {
                 // Convert the decompressed bytes to compressed (on the wire) bytes.
                 numBytes = decompressor.consumeBytes(stream.id(), numBytes);
             }
             try {
                 return flowController.consumeBytes(stream, numBytes);
             } catch (Http2Exception e) {
                 throw e;
             } catch (Throwable t) {
                 // The stream should be closed at this point. We have already changed our state tracking the compressed
                 // bytes, and there is no guarantee we can recover if the underlying flow controller throws.
                 throw streamError(stream.id(), INTERNAL_ERROR, t, "Error while returning bytes to flow control window");
             }
         }
 
         @Override
         public int unconsumedBytes(Http2Stream stream) {
             return flowController.unconsumedBytes(stream);
         }
 
         @Override
         public int initialWindowSize(Http2Stream stream) {
             return flowController.initialWindowSize(stream);
         }
     }
 
     /**
      * Provides the state for stream {@code DATA} frame decompression.
      */
     private static final class Http2Decompressor {
         private final Decompressor decompressor;
         private int compressed;
         private int decompressed;
 
         Http2Decompressor(Decompressor decompressor) {
             this.decompressor = decompressor;
         }
 
         /**
          * Responsible for taking compressed bytes in and producing decompressed bytes.
          */
         Decompressor decompressor() {
             return decompressor;
         }
 
         /**
          * Increment the number of bytes received prior to doing any decompression.
          */
         void incrementCompressedBytes(int delta) {
             assert delta >= 0;
             compressed += delta;
         }
 
         /**
          * Increment the number of bytes after the decompression process.
          */
         void incrementDecompressedBytes(int delta) {
             assert delta >= 0;
             decompressed += delta;
         }
 
         /**
          * Determines the ratio between {@code numBytes} and {@link Http2Decompressor#decompressed}.
          * This ratio is used to decrement {@link Http2Decompressor#decompressed} and
          * {@link Http2Decompressor#compressed}.
          * @param streamId the stream ID
          * @param decompressedBytes The number of post-decompressed bytes to return to flow control
          * @return The number of pre-decompressed bytes that have been consumed.
          */
         int consumeBytes(int streamId, int decompressedBytes) throws Http2Exception {
             checkPositiveOrZero(decompressedBytes, "decompressedBytes");
             if (decompressed - decompressedBytes < 0) {
                 throw streamError(streamId, INTERNAL_ERROR,
                         "Attempting to return too many bytes for stream %d. decompressed: %d " +
                                 "decompressedBytes: %d", streamId, decompressed, decompressedBytes);
             }
             double consumedRatio = decompressedBytes / (double) decompressed;
             int consumedCompressed = Math.min(compressed, (int) Math.ceil(compressed * consumedRatio));
             if (compressed - consumedCompressed < 0) {
                 throw streamError(streamId, INTERNAL_ERROR,
                         "overflow when converting decompressed bytes to compressed bytes for stream %d." +
                                 "decompressedBytes: %d decompressed: %d compressed: %d consumedCompressed: %d",
                         streamId, decompressedBytes, decompressed, compressed, consumedCompressed);
             }
             decompressed -= decompressedBytes;
             compressed -= consumedCompressed;
 
             return consumedCompressed;
         }
     }
 }