/*

  * 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.edge;

 import java.io.DataInput;

 import java.io.DataOutput;

 import java.io.IOException;

 import java.util.Iterator;

 import javax.annotation.concurrent.NotThreadSafe;

 import org.apache.giraph.conf.ImmutableClassesGiraphConfiguration;

 import org.apache.giraph.utils.EdgeIterables;

 import org.apache.giraph.utils.Trimmable;

 import org.apache.hadoop.io.LongWritable;

 import org.apache.hadoop.io.NullWritable;

 import org.apache.hadoop.io.Writable;

 /**

  * Implementation of {@link org.apache.giraph.edge.OutEdges} with long ids

  * and null edge values, backed by a dynamic primitive array.

  * Parallel edges are allowed.

  * Note: this implementation is optimized for space usage,

  * but random access and edge removals are expensive.

  * Users of this class should explicitly call {@link #trim()} function

  * to compact in-memory representation after all updates are done.

  * Compacting object is expensive so should only be done once after bulk update.

  * Compaction can also be caused by serialization attempt or

  * by calling {@link #iterator()}

  */

 @NotThreadSafe

 public class LongDiffNullArrayEdges

     extends ConfigurableOutEdges<LongWritable, NullWritable>

     implements ReuseObjectsOutEdges<LongWritable, NullWritable>,

     MutableOutEdges<LongWritable, NullWritable>, Trimmable {

   /**

    * Compressed array of target vertex ids.

    */

   private LongDiffArray edges = new LongDiffArray();

   @Override

   public void setConf(ImmutableClassesGiraphConfiguration

                       <LongWritable, Writable, NullWritable> conf) {

     super.setConf(conf);

     edges.setUseUnsafeSerialization(conf.getUseUnsafeSerialization());

   }

   @Override

   public void initialize(

     Iterable<Edge<LongWritable, NullWritable>> edgeIterator

   ) {

     edges.initialize();

     EdgeIterables.initialize(this, edgeIterator);

     edges.trim();

   }

   @Override

   public void initialize(int capacity) {

     edges.initialize(capacity);

   }

   @Override

   public void initialize() {

     edges.initialize();

   }

   @Override

   public void add(Edge<LongWritable, NullWritable> edge) {

     edges.add(edge.getTargetVertexId().get());

   }

   @Override

   public void remove(LongWritable targetVertexId) {

     edges.remove(targetVertexId.get());

   }

   @Override

   public int size() {

     return edges.size();

   }

   @Override

   public Iterator<Edge<LongWritable, NullWritable>> iterator() {

     // Returns an iterator that reuses objects.

     // The downcast is fine because all concrete Edge implementations are

     // mutable, but we only expose the mutation functionality when appropriate.

     return (Iterator) mutableIterator();

   }

   @Override

   public Iterator<MutableEdge<LongWritable, NullWritable>> mutableIterator() {

     trim();

     return new Iterator<MutableEdge<LongWritable, NullWritable>>() {

       private final Iterator<LongWritable> reader = edges.iterator();

       /** Representative edge object. */

       private final MutableEdge<LongWritable, NullWritable> representativeEdge =

           EdgeFactory.createReusable(new LongWritable());

       @Override

       public boolean hasNext() {

         return reader.hasNext();

       }

       @Override

       public MutableEdge<LongWritable, NullWritable> next() {

         representativeEdge.getTargetVertexId().set(reader.next().get());

         return representativeEdge;

       }

       @Override

       public void remove() {

         reader.remove();

       }

     };

   }

   @Override

   public void write(DataOutput out) throws IOException {

     edges.write(out);

   }

   @Override

   public void readFields(DataInput in) throws IOException {

     edges.readFields(in);

   }

   /**

    * This function takes all recent updates and stores them efficiently.

    * It is safe to call this function multiple times.

    */

   @Override

   public void trim() {

     edges.trim();

   }

 }