/**
 * 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.
 */
package org.apache.drill.exec.rpc;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.ByteToMessageDecoder;
import io.netty.handler.codec.CorruptedFrameException;

import java.util.List;

import org.apache.drill.exec.memory.BufferAllocator;

import com.google.protobuf.CodedInputStream;
import org.apache.drill.exec.exception.OutOfMemoryException;

/**
 * Modified version of {@link io.netty.handler.codec.protobuf.ProtobufVarint32FrameDecoder} that avoids bytebuf copy.
 * See the documentation there.
 */
public class ProtobufLengthDecoder extends ByteToMessageDecoder {
  static final org.slf4j.Logger logger = org.slf4j.LoggerFactory.getLogger(ProtobufLengthDecoder.class);

  private BufferAllocator allocator;
  private OutOfMemoryHandler outOfMemoryHandler;

  public ProtobufLengthDecoder(BufferAllocator allocator, OutOfMemoryHandler outOfMemoryHandler) {
    super();
    this.allocator = allocator;
    this.outOfMemoryHandler = outOfMemoryHandler;
  }


  @Override
  protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
    if (!ctx.channel().isOpen()) {
      if (in.readableBytes() > 0) {
        logger.info("Channel is closed, discarding remaining {} byte(s) in buffer.", in.readableBytes());
      }
      in.skipBytes(in.readableBytes());
      return;
    }

    in.markReaderIndex();
    final byte[] buf = new byte[5];
    for (int i = 0; i < buf.length; i++) {
      if (!in.isReadable()) {
        in.resetReaderIndex();
        return;
      }

      buf[i] = in.readByte();
      if (buf[i] >= 0) {

        int length = CodedInputStream.newInstance(buf, 0, i + 1).readRawVarint32();

        if (length < 0) {
          throw new CorruptedFrameException("negative length: " + length);
        }
        if (length == 0) {
          throw new CorruptedFrameException("Received a message of length 0.");
        }

        if (in.readableBytes() < length) {
          in.resetReaderIndex();
          return;
        } else {
          // need to make buffer copy, otherwise netty will try to refill this buffer if we move the readerIndex forward...
          // TODO: Can we avoid this copy?
          ByteBuf outBuf;
          try {
            outBuf = allocator.buffer(length);
          } catch (OutOfMemoryException e) {
            logger.warn("Failure allocating buffer on incoming stream due to memory limits.  Current Allocation: {}.", allocator.getAllocatedMemory());
            in.resetReaderIndex();
            outOfMemoryHandler.handle();
            return;
          }
          outBuf.writeBytes(in, in.readerIndex(), length);

          in.skipBytes(length);

          if (RpcConstants.EXTRA_DEBUGGING) {
            logger.debug(String.format(
                "ReaderIndex is %d after length header of %d bytes and frame body of length %d bytes.",
                in.readerIndex(), i + 1, length));
          }

          out.add(outBuf);
          return;
        }
      }
    }

    // Couldn't find the byte whose MSB is off.
    throw new CorruptedFrameException("length wider than 32-bit");

  }

  @Override
  public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
    ctx.fireChannelReadComplete();
  }

}