/*

  * 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.ints.IntArrayList;

 import it.unimi.dsi.fastutil.ints.IntIterator;

 import java.io.DataInput;

 import java.io.DataOutput;

 import java.io.IOException;

 import java.util.Iterator;

 import org.apache.giraph.utils.EdgeIterables;

 import org.apache.giraph.utils.Trimmable;

 import org.apache.hadoop.io.IntWritable;

 import org.apache.hadoop.io.NullWritable;

 import com.google.common.collect.UnmodifiableIterator;

 /**

  * Implementation of {@link OutEdges} with int ids and null edge

  * values, backed by dynamic primitive array.

  * Parallel edges are allowed.

  * Note: this implementation is optimized for space usage,

  * but edge removals are expensive.

  */

 public class IntNullArrayEdges

     implements ReuseObjectsOutEdges<IntWritable, NullWritable>, Trimmable {

   /** Array of target vertex ids */

   private IntArrayList neighbors;

   @Override

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

     EdgeIterables.initialize(this, edges);

   }

   @Override

   public void initialize(int capacity) {

     neighbors = new IntArrayList(capacity);

   }

   @Override

   public void initialize() {

     neighbors = new IntArrayList();

   }

   @Override

   public int size() {

     return neighbors.size();

   }

   @Override

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

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

   }

   /**

    * Remove edge at position i.

    *

    * @param i Position of edge to be removed

    */

   private void removeAt(int i) {

     // The order of the edges is irrelevant, so we can simply replace

     // the deleted edge with the rightmost element, thus achieving constant

     // time.

     if (i == neighbors.size() - 1) {

       neighbors.popInt();

     } else {

       neighbors.set(i, neighbors.popInt());

     }

   }

   @Override

   public void remove(IntWritable targetVertexId) {

     // Thanks to the constant-time implementation of removeAt(int),

     // we can remove all matching edges in linear time.

     for (int i = neighbors.size() - 1; i >= 0; --i) {

       if (neighbors.getInt(i) == targetVertexId.get()) {

         removeAt(i);

       }

     }

   }

   @Override

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

     // Returns an iterator that reuses objects.

     return new UnmodifiableIterator<Edge<IntWritable, NullWritable>>() {

       /** Wrapped neighbors iterator. */

       private final IntIterator neighborsIt = neighbors.iterator();

       /** Representative edge object. */

       private final Edge<IntWritable, NullWritable> representativeEdge =

           EdgeFactory.create(new IntWritable(), NullWritable.get());

       @Override

       public boolean hasNext() {

         return neighborsIt.hasNext();

       }

       @Override

       public Edge<IntWritable, NullWritable> next() {

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

         return representativeEdge;

       }

     };

   }

   @Override

   public void write(DataOutput out) throws IOException {

     out.writeInt(neighbors.size());

     IntIterator iterator = neighbors.iterator();

     while (iterator.hasNext()) {

       out.writeInt(iterator.nextInt());

     }

   }

   @Override

   public void readFields(DataInput in) throws IOException {

     int numEdges = in.readInt();

     initialize(numEdges);

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

       neighbors.add(in.readInt());

     }

   }

   @Override

   public void trim() {

     neighbors.trim();

   }

 }