/*
    * 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.hadoop.hbase.ipc;
  
  import java.io.IOException;
  import java.nio.ByteBuffer;
  import java.nio.channels.GatheringByteChannel;
  import java.util.ArrayList;
  import java.util.List;
  
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  
  /**
   * Chain of ByteBuffers.
   * Used writing out an array of byte buffers.  Writes in chunks.
   */
  @InterfaceAudience.Private
  class BufferChain {
    private final ByteBuffer[] buffers;
    private int remaining = 0;
    private int bufferOffset = 0;
  
    BufferChain(ByteBuffer ... buffers) {
      // Some of the incoming buffers can be null
      List<ByteBuffer> bbs = new ArrayList<ByteBuffer>(buffers.length);
      for (ByteBuffer b : buffers) {
        if (b == null) continue;
        bbs.add(b);
        this.remaining += b.remaining();
      }
      this.buffers = bbs.toArray(new ByteBuffer[bbs.size()]);
    }
  
    /**
     * Expensive.  Makes a new buffer to hold a copy of what is in contained ByteBuffers.  This
     * call drains this instance; it cannot be used subsequent to the call.
     * @return A new byte buffer with the content of all contained ByteBuffers.
     */
    byte [] getBytes() {
      if (!hasRemaining()) throw new IllegalAccessError();
      byte [] bytes = new byte [this.remaining];
      int offset = 0;
      for (ByteBuffer bb: this.buffers) {
        int length = bb.remaining();
        bb.get(bytes, offset, length);
        offset += length;
      }
      return bytes;
    }
  
    boolean hasRemaining() {
      return remaining > 0;
    }
  
    /**
     * Write out our chain of buffers in chunks
     * @param channel Where to write
     * @param chunkSize Size of chunks to write.
     * @return Amount written.
     * @throws IOException
     */
    long write(GatheringByteChannel channel, int chunkSize) throws IOException {
      int chunkRemaining = chunkSize;
      ByteBuffer lastBuffer = null;
      int bufCount = 0;
      int restoreLimit = -1;
  
      while (chunkRemaining > 0 && bufferOffset + bufCount < buffers.length) {
        lastBuffer = buffers[bufferOffset + bufCount];
        if (!lastBuffer.hasRemaining()) {
          bufferOffset++;
          continue;
        }
        bufCount++;
        if (lastBuffer.remaining() > chunkRemaining) {
          restoreLimit = lastBuffer.limit();
          lastBuffer.limit(lastBuffer.position() + chunkRemaining);
          chunkRemaining = 0;
          break;
        } else {
          chunkRemaining -= lastBuffer.remaining();
        }
      }
      assert lastBuffer != null;
     if (chunkRemaining == chunkSize) {
       assert !hasRemaining();
       // no data left to write
       return 0;
     }
     try {
       long ret = channel.write(buffers, bufferOffset, bufCount);
       if (ret > 0) {
         remaining = (int) (remaining - ret);
       }
       return ret;
     } finally {
       if (restoreLimit >= 0) {
         lastBuffer.limit(restoreLimit);
       }
     }
   }
 }