/*

  * 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 java.util.NoSuchElementException;

 import org.apache.giraph.conf.ImmutableClassesGiraphConfigurable;

 import org.apache.giraph.conf.ImmutableClassesGiraphConfiguration;

 import org.apache.giraph.types.ops.PrimitiveIdTypeOps;

 import org.apache.giraph.types.ops.TypeOpsUtils;

 import org.apache.giraph.types.ops.collections.array.WArrayList;

 import org.apache.giraph.utils.EdgeIterables;

 import org.apache.hadoop.io.NullWritable;

 import org.apache.hadoop.io.Writable;

 import org.apache.hadoop.io.WritableComparable;

 /**

  * Implementation of {@link OutEdges} with IDs and null edge values having

  * their TypeOps.

  * 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.

  *

  * @param <I> Vertex id type

  */

 public class IdAndNullArrayEdges<I extends WritableComparable>

   implements ReuseObjectsOutEdges<I, NullWritable>,

   MutableOutEdges<I, NullWritable>,

   ImmutableClassesGiraphConfigurable<I, Writable, NullWritable> {

   /** Array of target vertex ids. */

   private WArrayList<I> neighbors;

   @Override

   public

   ImmutableClassesGiraphConfiguration<I, Writable, NullWritable> getConf() {

     throw new UnsupportedOperationException();

   }

   @Override

   public void setConf(

       ImmutableClassesGiraphConfiguration<I, Writable, NullWritable> conf) {

     PrimitiveIdTypeOps<I> idTypeOps =

         TypeOpsUtils.getPrimitiveIdTypeOps(conf.getVertexIdClass());

     neighbors = idTypeOps.createArrayList(10);

     if (!conf.getEdgeValueClass().equals(NullWritable.class)) {

       throw new IllegalArgumentException(

           "IdAndNullArrayEdges can be used only with NullWritable " +

           "as edgeValueClass, not with " + conf.getEdgeValueClass());

     }

   }

   @Override

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

     EdgeIterables.initialize(this, edges);

   }

   @Override

   public void initialize(int capacity) {

     neighbors.clear();

     neighbors.setCapacity(capacity);

   }

   @Override

   public void initialize() {

     initialize(10);

   }

   @Override

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

     neighbors.addW(edge.getTargetVertexId());

   }

   /**

    * If the backing array is more than four times as big as the number of

    * elements, reduce to 2 times current size.

    */

   private void trim() {

     if (neighbors.capacity() > 4 * neighbors.size()) {

       neighbors.setCapacity(neighbors.size() * 2);

     }

   }

   /**

    * 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.

     I tmpValue = neighbors.getElementTypeOps().create();

     neighbors.popIntoW(tmpValue);

     if (i != neighbors.size()) {

       neighbors.setW(i, tmpValue);

     }

     // If needed after the removal, trim the array.

     trim();

   }

   @Override

   public void remove(I targetVertexId) {

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

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

     I tmpValue = neighbors.getElementTypeOps().create();

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

       neighbors.getIntoW(i, tmpValue);

       if (tmpValue.equals(targetVertexId)) {

         removeAt(i);

       }

     }

   }

   @Override

   public int size() {

     return neighbors.size();

   }

   @Override

   public Iterator<Edge<I, 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<I, NullWritable>> mutableIterator() {

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

       /** Current position in the array. */

       private int offset = 0;

       /** Representative edge object. */

       private final MutableEdge<I, NullWritable> representativeEdge =

           EdgeFactory.createReusable(neighbors.getElementTypeOps().create());

       @Override

       public boolean hasNext() {

         return offset < neighbors.size();

       }

       @Override

       public MutableEdge<I, NullWritable> next() {

         if (!hasNext()) {

           throw new NoSuchElementException();

         }

         neighbors.getIntoW(offset++, representativeEdge.getTargetVertexId());

         return representativeEdge;

       }

       @Override

       public void remove() {

         // Since removeAt() might replace the deleted edge with the last edge

         // in the array, we need to decrease the offset so that the latter

         // won't be skipped.

         removeAt(--offset);

       }

     };

   }

   @Override

   public void write(DataOutput out) throws IOException {

     neighbors.write(out);

   }

   @Override

   public void readFields(DataInput in) throws IOException {

     neighbors.readFields(in);

   }

 }