/*

  * 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.Maps;

 import org.apache.giraph.utils.EdgeIterables;

 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.HashMap;

 import java.util.Iterator;

 import java.util.Map;

 /**

  * {@link OutEdges} implementation backed by a {@link HashMap}.

  * Parallel edges are not allowed.

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

  * but uses more space.

  *

  * @param <I> Vertex id

  * @param <E> Edge value

  */

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

     extends ConfigurableOutEdges<I, E>

     implements StrictRandomAccessOutEdges<I, E>,

     MutableOutEdges<I, E> {

   /** Map from target vertex id to edge value. */

   private HashMap<I, E> edgeMap;

   @Override

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

     EdgeIterables.initialize(this, edges);

   }

   @Override

   public void initialize(int capacity) {

     edgeMap = Maps.newHashMapWithExpectedSize(capacity);

   }

   @Override

   public void initialize() {

     edgeMap = Maps.newHashMap();

   }

   @Override

   public void add(Edge<I, E> edge) {

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

   }

   @Override

   public void remove(I targetVertexId) {

     edgeMap.remove(targetVertexId);

   }

   @Override

   public E getEdgeValue(I targetVertexId) {

     return edgeMap.get(targetVertexId);

   }

   @Override

   public void setEdgeValue(I targetVertexId, E edgeValue) {

     if (edgeMap.containsKey(targetVertexId)) {

       edgeMap.put(targetVertexId, edgeValue);

     }

   }

   @Override

   public int size() {

     return edgeMap.size();

   }

   @Override

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

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

       /** Wrapped map iterator. */

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

           edgeMap.entrySet().iterator();

       /** Representative edge object. */

       private MapMutableEdge<I, E> representativeEdge =

           new MapMutableEdge<I, E>();

       @Override

       public boolean hasNext() {

         return mapIterator.hasNext();

       }

       @Override

       public MutableEdge<I, E> next() {

         representativeEdge.setEntry(mapIterator.next());

         return representativeEdge;

       }

       @Override

       public void remove() {

         mapIterator.remove();

       }

     };

   }

   @Override

   public void write(DataOutput out) throws IOException {

     out.writeInt(edgeMap.size());

     for (Map.Entry<I, E> entry : edgeMap.entrySet()) {

       entry.getKey().write(out);

       entry.getValue().write(out);

     }

   }

   @Override

   public void readFields(DataInput in) throws IOException {

     int numEdges = in.readInt();

     initialize(numEdges);

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

       I targetVertexId = getConf().createVertexId();

       targetVertexId.readFields(in);

       E edgeValue = getConf().createEdgeValue();

       edgeValue.readFields(in);

       edgeMap.put(targetVertexId, edgeValue);

     }

   }

 }