/*

  * 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.giraph.edge.OutEdges;

 import org.apache.giraph.graph.Vertex;

 import org.apache.hadoop.io.Writable;

 import org.apache.hadoop.io.WritableComparable;

 import java.io.IOException;

 /**

  * Iterates over vertices stored in an ExtendedDataOutput such that

  * the ownership of the vertex id can be transferred to another object.

  * This optimization cuts down on the number of objects instantiated and

  * garbage collected

  *

  * @param <I> Vertex id

  * @param <V> Vertex value

  * @param <E> Edge value

  */

 public class VertexIterator<I extends WritableComparable,

     V extends Writable, E extends Writable> {

   /** Reader of the serialized edges */

   private final ExtendedDataInput extendedDataInput;

   /** Current vertex */

   private Vertex<I, V, E> vertex;

   /** Configuration */

   private final ImmutableClassesGiraphConfiguration<I, V, E> configuration;

   /**

    * Constructor.

    *

    * @param extendedDataOutput Extended data output

    * @param configuration Configuration

    */

   public VertexIterator(

       ExtendedDataOutput extendedDataOutput,

       ImmutableClassesGiraphConfiguration<I, V, E> configuration) {

     extendedDataInput = configuration.createExtendedDataInput(

         extendedDataOutput.getByteArray(), 0, extendedDataOutput.getPos());

     this.configuration = configuration;

     resetEmptyVertex();

   }

   /**

    * Reset the empty Vertex to an initial state.

    */

   private void resetEmptyVertex() {

     vertex = configuration.createVertex();

     I id = configuration.createVertexId();

     V value = configuration.createVertexValue();

     OutEdges<I, E> edges = configuration.createOutEdges();

     vertex.initialize(id, value, edges);

   }

   /**

    * Returns true if the iteration has more elements.

    *

    * @return True if the iteration has more elements.

    */

   public boolean hasNext() {

     return !extendedDataInput.endOfInput();

   }

   /**

    * Moves to the next element in the iteration.

    */

   public void next() {

     // If the vertex was released, create another one

     if (vertex == null) {

       resetEmptyVertex();

     }

     // If the vertex id was released, create another one

     if (vertex.getId() == null) {

       vertex.initialize(configuration.createVertexId(), vertex.getValue());

     }

     try {

       WritableUtils.reinitializeVertexFromDataInput(

           extendedDataInput, vertex, configuration);

     } catch (IOException e) {

       throw new IllegalStateException("next: IOException", e);

     }

   }

   /**

    * Get the current vertex id.  Ihis object's contents are only guaranteed

    * until next() is called.  To take ownership of this object call

    * releaseCurrentVertexId() after getting a reference to this object.

    *

    * @return Current vertex id

    */

   public I getCurrentVertexId() {

     return vertex.getId();

   }

   /**

    * The backing store of the current vertex id is now released.

    * Further calls to getCurrentVertexId () without calling next()

    * will return null.

    *

    * @return Current vertex id that was released

    */

   public I releaseCurrentVertexId() {

     I releasedVertexId = vertex.getId();

     vertex.initialize(null, vertex.getValue());

     return releasedVertexId;

   }

   public Vertex<I, V, E> getVertex() {

     return vertex;

   }

   /**

    * Release the ownership of the Vertex object to the caller

    *

    * @return Released Vertex object

    */

   public Vertex<I, V, E> releaseVertex() {

     Vertex<I, V, E> releasedVertex = vertex;

     vertex = null;

     return releasedVertex;

   }

 }