/*

  * 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.giraph.comm.aggregators;

 import java.io.IOException;

 import org.apache.giraph.utils.ExtendedDataOutput;

 import org.apache.giraph.utils.UnsafeByteArrayOutputStream;

 /**

  * Wrapper for output stream which keeps the place in the beginning for the

  * count of objects which were written to it

  */

 public abstract class CountingOutputStream {

   /** DataOutput to which subclasses will be writing data */

   protected ExtendedDataOutput dataOutput;

   /** Counter for objects which were written to the stream */

   private int counter;

   /**

    * Default constructor

    */

   public CountingOutputStream() {

     dataOutput = new UnsafeByteArrayOutputStream();

     reset();

   }

   /**

    * Subclasses should call this method when an object is written

    */

   protected void incrementCounter() {

     counter++;

   }

   /**

    * Get the number of bytes in the stream

    *

    * @return Number of bytes

    */

   protected int getSize() {

     return dataOutput.getPos();

   }

   /**

    * Returns all the data from the stream and clears it.

    *

    * @return Number of objects followed by the data written to the stream

    */

   public byte[] flush() {

     dataOutput.writeInt(0, counter);

     // Actual flush not required, this is a byte array

     byte[] ret = dataOutput.toByteArray();

     reset();

     return ret;

   }

   /**

    * Reset the stream

    */

   private void reset() {

     dataOutput.reset();

     // reserve the place for count to be written in the end

     try {

       dataOutput.writeInt(0);

     } catch (IOException e) {

       throw new IllegalStateException("reset: Got IOException", e);

     }

     counter = 0;

   }

 }