/*
    * 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.giraph.conf.ImmutableClassesGiraphConfiguration;
  import org.apache.hadoop.io.WritableComparable;
  
  /**
   * Common implementation for VertexIdEdgeIterator, VertexIdMessageIterator
   * and VertexIdMessageBytesIterator.
   *
   * @param <I> Vertex id
   */
  public abstract class ByteStructVertexIdIterator<I extends WritableComparable>
    implements VertexIdIterator<I> {
    /** Reader of the serialized edges */
    protected final ExtendedDataInput extendedDataInput;
  
    /** Current vertex id */
    protected I vertexId;
  
    /**
     * Constructor.
     *
     * @param extendedDataOutput Extended data output
     * @param conf Configuration
     */
    public ByteStructVertexIdIterator(
      ExtendedDataOutput extendedDataOutput,
      ImmutableClassesGiraphConfiguration<I, ?, ?> conf) {
      if (extendedDataOutput != null && conf != null) {
        extendedDataInput = conf.createExtendedDataInput(extendedDataOutput);
      } else {
        throw new IllegalStateException("Cannot instantiate vertexIdIterator " +
          "with null arguments");
      }
    }
  
    @Override
    public boolean hasNext() {
      return !extendedDataInput.endOfInput();
    }
  
    @Override
    public I getCurrentVertexId() {
      return vertexId;
    }
  
    @Override
    public I releaseCurrentVertexId() {
      I releasedVertexId = vertexId;
      vertexId = null;
      return releasedVertexId;
    }
  }