/*
    * ====================================================================
    * 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.
   * ====================================================================
   *
   * This software consists of voluntary contributions made by many
   * individuals on behalf of the Apache Software Foundation.  For more
   * information on the Apache Software Foundation, please see
   * <http://www.apache.org/>.
   *
   */
  package org.apache.hc.core5.http2.impl.nio;
  
  import java.io.IOException;
  import java.nio.ByteBuffer;
  import java.nio.channels.GatheringByteChannel;
  import java.nio.channels.WritableByteChannel;
  
  import org.apache.hc.core5.http2.H2ConnectionException;
  import org.apache.hc.core5.http2.H2Error;
  import org.apache.hc.core5.http2.H2TransportMetrics;
  import org.apache.hc.core5.http2.frame.FrameConsts;
  import org.apache.hc.core5.http2.frame.RawFrame;
  import org.apache.hc.core5.http2.impl.BasicH2TransportMetrics;
  import org.apache.hc.core5.util.Args;
  
  /**
   * Frame output buffer for HTTP/2 non-blocking connections.
   *
   * @since 5.0
   */
  public final class FrameOutputBuffer {
  
      private final BasicH2TransportMetrics metrics;
      private final int maxFramePayloadSize;
      private final ByteBuffer buffer;
  
      public FrameOutputBuffer(final BasicH2TransportMetrics metrics, final int maxFramePayloadSize) {
          Args.notNull(metrics, "HTTP2 transport metrics");
          Args.positive(maxFramePayloadSize, "Maximum payload size");
          this.metrics = metrics;
          this.maxFramePayloadSize = maxFramePayloadSize;
          this.buffer = ByteBuffer.allocate(FrameConsts.HEAD_LEN + maxFramePayloadSize);
      }
  
      public FrameOutputBuffer(final int maxFramePayloadSize) {
          this(new BasicH2TransportMetrics(), maxFramePayloadSize);
      }
  
      public void write(final RawFrame frame, final WritableByteChannel channel) throws IOException {
          Args.notNull(frame, "Frame");
  
          final ByteBuffer payload = frame.getPayload();
          if (payload != null && payload.remaining() > maxFramePayloadSize) {
              throw new H2ConnectionException(H2Error.FRAME_SIZE_ERROR, "Frame size exceeds maximum");
          }
  
          buffer.putInt((payload != null ? payload.remaining() << 8 : 0) | (frame.getType() & 0xff));
          buffer.put((byte) (frame.getFlags() & 0xff));
          buffer.putInt(frame.getStreamId());
  
          if (payload != null) {
              if (channel instanceof GatheringByteChannel) {
                  buffer.flip();
                  ((GatheringByteChannel) channel).write(new ByteBuffer[]{buffer, payload});
                  buffer.compact();
                  if (payload.hasRemaining()) {
                      buffer.put(payload);
                  }
              } else {
                  buffer.put(payload);
              }
          }
  
          flush(channel);
  
          metrics.incrementFramesTransferred();
      }
  
      public void flush(final WritableByteChannel channel) throws IOException {
          if (buffer.position() > 0) {
              buffer.flip();
              try {
                  final int bytesWritten = channel.write(buffer);
                 if (bytesWritten > 0) {
                     metrics.incrementBytesTransferred(bytesWritten);
                 }
             } finally {
                 buffer.compact();
             }
         }
     }
 
     public boolean isEmpty() {
         return buffer.position() == 0;
     }
 
     public H2TransportMetrics getMetrics() {
         return metrics;
     }
 
 }