/*

  * 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 com.google.common.collect.ArrayListMultimap;

 import com.google.common.collect.UnmodifiableIterator;

 import org.apache.giraph.utils.EdgeIterables;

 import org.apache.giraph.utils.Trimmable;

 import org.apache.hadoop.io.Writable;

 import org.apache.hadoop.io.WritableComparable;

 import java.io.DataInput;

 import java.io.DataOutput;

 import java.io.IOException;

 import java.util.Iterator;

 import java.util.Map;

 /**

  * {@link OutEdges} implementation backed by an {@link ArrayListMultimap}.

  * Parallel edges are allowed.

  * Note: this implementation is optimized for fast mutations,

  * but uses more space.

  *

  * @param <I> Vertex id

  * @param <E> Edge value

  */

 public class HashMultimapEdges<I extends WritableComparable, E extends Writable>

     extends ConfigurableOutEdges<I, E>

     implements MultiRandomAccessOutEdges<I, E>, Trimmable {

   /** Multimap from target vertex id to edge values. */

   private ArrayListMultimap<I, E> edgeMultimap;

   @Override

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

     EdgeIterables.initialize(this, edges);

   }

   /**

    * Additional initialization method tailored to the underlying multimap

    * implementation.

    *

    * @param expectedNeighbors Expected number of unique neighbors

    * @param expectedEdgesPerNeighbor Expected number of edges per neighbor

    */

   public void initialize(int expectedNeighbors, int expectedEdgesPerNeighbor) {

     edgeMultimap = ArrayListMultimap.create(expectedNeighbors,

         expectedEdgesPerNeighbor);

   }

   @Override

   public void initialize(int capacity) {

     // To be conservative in terms of space usage, we assume that the initial

     // number of values per key is 1.

     initialize(capacity, 1);

   }

   @Override

   public void initialize() {

     edgeMultimap = ArrayListMultimap.create();

   }

   @Override

   public void add(Edge<I, E> edge) {

     edgeMultimap.put(edge.getTargetVertexId(), edge.getValue());

   }

   @Override

   public void remove(I targetVertexId) {

     edgeMultimap.removeAll(targetVertexId);

   }

   @Override

   public Iterable<E> getAllEdgeValues(I targetVertexId) {

     return edgeMultimap.get(targetVertexId);

   }

   @Override

   public int size() {

     return edgeMultimap.size();

   }

   @Override

   public Iterator<Edge<I, E>> iterator() {

     // Returns an iterator that reuses objects.

     return new UnmodifiableIterator<Edge<I, E>>() {

       /** Wrapped map iterator. */

       private Iterator<Map.Entry<I, E>> mapIterator =

           edgeMultimap.entries().iterator();

       /** Representative edge object. */

       private ReusableEdge<I, E> representativeEdge =

           getConf().createReusableEdge();

       @Override

       public boolean hasNext() {

         return mapIterator.hasNext();

       }

       @Override

       public Edge<I, E> next() {

         Map.Entry<I, E> nextEntry = mapIterator.next();

         representativeEdge.setTargetVertexId(nextEntry.getKey());

         representativeEdge.setValue(nextEntry.getValue());

         return representativeEdge;

       }

     };

   }

   @Override

   public void write(DataOutput out) throws IOException {

     // We write both the total number of edges and the number of unique

     // neighbors.

     out.writeInt(edgeMultimap.size());

     out.writeInt(edgeMultimap.keys().size());

     for (Map.Entry<I, E> edge : edgeMultimap.entries()) {

       edge.getKey().write(out);

       edge.getValue().write(out);

     }

   }

   @Override

   public void readFields(DataInput in) throws IOException {

     // Given the total number of pairs and the number of unique neighbors,

     // we are able to compute the average number of edges per neighbors.

     int numEdges = in.readInt();

     int numNeighbors = in.readInt();

     initialize(numEdges, numNeighbors == 0 ? 0 : numEdges / numNeighbors);

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

       I targetVertexId = getConf().createVertexId();

       targetVertexId.readFields(in);

       E edgeValue = getConf().createEdgeValue();

       edgeValue.readFields(in);

       edgeMultimap.put(targetVertexId, edgeValue);

     }

   }

   @Override

   public void trim() {

     edgeMultimap.trimToSize();

   }

 }