/*

  * 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.Long2ByteMap;

 import it.unimi.dsi.fastutil.longs.Long2ByteOpenHashMap;

 import it.unimi.dsi.fastutil.objects.ObjectIterator;

 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.ByteWritable;

 import org.apache.hadoop.io.LongWritable;

 import com.google.common.collect.UnmodifiableIterator;

 /**

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

  * backed by a {@link Long2ByteOpenHashMap}.

  * 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}.

  */

 public class LongByteHashMapEdges

     implements StrictRandomAccessOutEdges<LongWritable, ByteWritable>,

     ReuseObjectsOutEdges<LongWritable, ByteWritable>,

     MutableOutEdges<LongWritable, ByteWritable>, Trimmable {

   /** Hash map from target vertex id to edge value. */

   private Long2ByteOpenHashMap edgeMap;

   /** Representative edge value object, used by getEdgeValue(). */

   private ByteWritable representativeEdgeValue;

   @Override

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

     EdgeIterables.initialize(this, edges);

   }

   @Override

   public void initialize(int capacity) {

     edgeMap = new Long2ByteOpenHashMap(capacity);

   }

   @Override

   public void initialize() {

     edgeMap = new Long2ByteOpenHashMap();

   }

   @Override

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

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

   }

   @Override

   public void remove(LongWritable targetVertexId) {

     edgeMap.remove(targetVertexId.get());

   }

   @Override

   public ByteWritable getEdgeValue(LongWritable targetVertexId) {

     if (!edgeMap.containsKey(targetVertexId.get())) {

       return null;

     }

     if (representativeEdgeValue == null) {

       representativeEdgeValue = new ByteWritable();

     }

     representativeEdgeValue.set(edgeMap.get(targetVertexId.get()));

     return representativeEdgeValue;

   }

   @Override

   public void setEdgeValue(LongWritable targetVertexId,

                            ByteWritable edgeValue) {

     if (edgeMap.containsKey(targetVertexId.get())) {

       edgeMap.put(targetVertexId.get(), edgeValue.get());

     }

   }

   @Override

   public int size() {

     return edgeMap.size();

   }

   @Override

   public Iterator<Edge<LongWritable, ByteWritable>> iterator() {

     // Returns an iterator that reuses objects.

     return new UnmodifiableIterator<Edge<LongWritable, ByteWritable>>() {

       /** Wrapped map iterator. */

       private final ObjectIterator<Long2ByteMap.Entry> mapIterator =

           edgeMap.long2ByteEntrySet().fastIterator();

       /** Representative edge object. */

       private final ReusableEdge<LongWritable, ByteWritable>

       representativeEdge =

           EdgeFactory.createReusable(new LongWritable(), new ByteWritable());

       @Override

       public boolean hasNext() {

         return mapIterator.hasNext();

       }

       @Override

       public Edge<LongWritable, ByteWritable> next() {

         Long2ByteMap.Entry nextEntry = mapIterator.next();

         representativeEdge.getTargetVertexId().set(nextEntry.getLongKey());

         representativeEdge.getValue().set(nextEntry.getByteValue());

         return representativeEdge;

       }

     };

   }

   @Override

   public void trim() {

     edgeMap.trim();

   }

   /** Helper class for a mutable edge that modifies the backing map entry. */

   private static class LongByteHashMapMutableEdge

       extends DefaultEdge<LongWritable, ByteWritable> {

     /** Backing entry for the edge in the map. */

     private Long2ByteMap.Entry entry;

     /** Constructor. */

     public LongByteHashMapMutableEdge() {

       super(new LongWritable(), new ByteWritable());

     }

     /**

      * Make the edge point to the given entry in the backing map.

      *

      * @param entry Backing entry

      */

     public void setEntry(Long2ByteMap.Entry entry) {

       // Update the id and value objects from the superclass.

       getTargetVertexId().set(entry.getLongKey());

       getValue().set(entry.getByteValue());

       // Update the entry.

       this.entry = entry;

     }

     @Override

     public void setValue(ByteWritable value) {

       // Update the value object from the superclass.

       getValue().set(value.get());

       // Update the value stored in the backing map.

       entry.setValue(value.get());

     }

   }

   @Override

   public Iterator<MutableEdge<LongWritable, ByteWritable>> mutableIterator() {

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

       /**

        * Wrapped map iterator.

        * Note: we cannot use the fast iterator in this case,

        * because we need to call setValue() on an entry.

        */

       private final ObjectIterator<Long2ByteMap.Entry> mapIterator =

           edgeMap.long2ByteEntrySet().iterator();

       /** Representative edge object. */

       private final LongByteHashMapMutableEdge representativeEdge =

           new LongByteHashMapMutableEdge();

       @Override

       public boolean hasNext() {

         return mapIterator.hasNext();

       }

       @Override

       public MutableEdge<LongWritable, ByteWritable> 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 (Long2ByteMap.Entry entry : edgeMap.long2ByteEntrySet()) {

       out.writeLong(entry.getLongKey());

       out.writeByte(entry.getByteValue());

     }

   }

   @Override

   public void readFields(DataInput in) throws IOException {

     int numEdges = in.readInt();

     initialize(numEdges);

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

       edgeMap.put(in.readLong(), in.readByte());

     }

   }

 }