/*
    * 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.utils;
  
  import org.apache.hadoop.io.Writable;
  import org.apache.hadoop.io.WritableComparable;
  
  import java.io.IOException;
  import javax.annotation.concurrent.NotThreadSafe;
  
  /**
   * Special iterator that reuses vertex ids and messages bytes so that the
   * lifetime of the object is only until next() is called.
   *
   * Vertex id ownership can be released if desired through
   * releaseCurrentVertexId().  This optimization allows us to cut down
   * on the number of objects instantiated and garbage collected.  Messages
   * can only be copied to an ExtendedDataOutput object
   *
   * @param <I> vertexId type parameter
   * @param <M> message type parameter
   */
  @NotThreadSafe
  public abstract class ByteStructVertexIdMessageBytesIterator<I
    extends WritableComparable, M extends Writable>
    extends ByteStructVertexIdDataIterator<I, M>
    implements VertexIdMessageBytesIterator<I, M> {
    /** Last message offset */
    protected int messageOffset = -1;
    /** Number of bytes in the last message */
    protected int messageBytes = -1;
  
    /**
     * Constructor with vertexIdData
     *
     * @param vertexIdData vertexIdData
     */
    public ByteStructVertexIdMessageBytesIterator(
      AbstractVertexIdData<I, M> vertexIdData) {
      super(vertexIdData);
    }
  
    /**
     * Moves to the next element in the iteration.
     */
    @Override
    public void next() {
      if (vertexId == null) {
        vertexId = vertexIdData.getConf().createVertexId();
      }
  
      try {
        vertexId.readFields(extendedDataInput);
        messageBytes = extendedDataInput.readInt();
        messageOffset = extendedDataInput.getPos();
        if (extendedDataInput.skipBytes(messageBytes) != messageBytes) {
          throw new IllegalStateException("next: Failed to skip " +
              messageBytes);
        }
      } catch (IOException e) {
        throw new IllegalStateException("next: IOException", e);
      }
    }
  }