/*

  * 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 it.unimi.dsi.fastutil.longs.LongIterator;

 import it.unimi.dsi.fastutil.longs.LongOpenHashSet;

 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 java.io.DataInput;

 import java.io.DataOutput;

 import java.io.IOException;

 import java.util.Iterator;

 /**

  * {@link OutEdges} implementation with long ids and null edge values,

  * backed by a {@link LongOpenHashSet}.

  * Parallel edges are not allowed.

  * Note: this implementation is optimized for fast random access and mutations,

  * and uses less space than a generic {@link HashMapEdges} (but more than

  * {@link LongNullArrayEdges}.

  */

 public class LongNullHashSetEdges

     implements ReuseObjectsOutEdges<LongWritable, NullWritable>,

     MutableOutEdges<LongWritable, NullWritable>,

     StrictRandomAccessOutEdges<LongWritable, NullWritable>,

     Trimmable {

   /** Hash set of target vertex ids. */

   private LongOpenHashSet neighbors;

   @Override

   public void initialize(Iterable<Edge<LongWritable, NullWritable>> edges) {

     EdgeIterables.initialize(this, edges);

   }

   @Override

   public void initialize(int capacity) {

     neighbors = new LongOpenHashSet(capacity);

   }

   @Override

   public void initialize() {

     neighbors = new LongOpenHashSet();

   }

   @Override

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

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

   }

   @Override

   public void remove(LongWritable targetVertexId) {

     neighbors.remove(targetVertexId.get());

   }

   @Override

   public int size() {

     return neighbors.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() {

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

       /** Wrapped neighbors iterator. */

       private LongIterator neighborsIt = neighbors.iterator();

       /** Representative edge object. */

       private ReusableEdge<LongWritable, NullWritable> representativeEdge =

           EdgeFactory.createReusable(new LongWritable());

       public boolean hasNext() {

         return neighborsIt.hasNext();

       }

       @Override

       public MutableEdge<LongWritable, NullWritable> next() {

         representativeEdge.getTargetVertexId().set(neighborsIt.nextLong());

         return representativeEdge;

       }

       @Override

       public void remove() {

         neighborsIt.remove();

       }

     };

   }

   @Override

   public void write(DataOutput out) throws IOException {

     out.writeInt(neighbors.size());

     LongIterator neighborsIt = neighbors.iterator();

     while (neighborsIt.hasNext()) {

       out.writeLong(neighborsIt.nextLong());

     }

   }

   @Override

   public void readFields(DataInput in) throws IOException {

     int numEdges = in.readInt();

     initialize(numEdges);

     for (int i = 0; i < numEdges; ++i) {

       neighbors.add(in.readLong());

     }

   }

   @Override

   public NullWritable getEdgeValue(LongWritable targetVertexId) {

     if (neighbors.contains(targetVertexId.get())) {

       return NullWritable.get();

     } else {

       return null;

     }

   }

   @Override

   public void setEdgeValue(LongWritable targetVertexId,

     NullWritable edgeValue) {

     // No operation.

     // Only set value for an existing edge.

     // If the edge exist, the Null value is already there.

   }

   @Override

   public void trim() {

     neighbors.trim();

   }

 }