/*

  * 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.PrimitiveTypeOps;

 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.Writable;

 import org.apache.hadoop.io.WritableComparable;

 import com.google.common.collect.UnmodifiableIterator;

 /**

  * Implementation of {@link OutEdges} with IDs and Edge values having their

  * TypeOps.

  * Data is 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

  * @param <E> Edge value type

  */

 public class IdAndValueArrayEdges<I extends WritableComparable,

     E extends Writable> implements ReuseObjectsOutEdges<I, E>,

     MutableOutEdges<I, E>,

     ImmutableClassesGiraphConfigurable<I, Writable, E> {

   /** Array of target vertex ids. */

   private WArrayList<I> neighborIds;

   /** Array of edge values. */

   private WArrayList<E> neighborEdgeValues;

   @Override

   public ImmutableClassesGiraphConfiguration<I, Writable, E> getConf() {

     throw new UnsupportedOperationException();

   }

   @Override

   public void setConf(

       ImmutableClassesGiraphConfiguration<I, Writable, E> conf) {

     PrimitiveIdTypeOps<I> idTypeOps =

         TypeOpsUtils.getPrimitiveIdTypeOps(conf.getVertexIdClass());

     neighborIds = idTypeOps.createArrayList(10);

     PrimitiveTypeOps<E> edgeTypeOps =

         TypeOpsUtils.getPrimitiveTypeOps(conf.getEdgeValueClass());

     neighborEdgeValues = edgeTypeOps.createArrayList(10);

   }

   @Override

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

     EdgeIterables.initialize(this, edges);

   }

   @Override

   public void initialize(int capacity) {

     neighborIds.clear();

     neighborIds.setCapacity(capacity);

     neighborEdgeValues.clear();

     neighborEdgeValues.setCapacity(capacity);

   }

   @Override

   public void initialize() {

     initialize(10);

   }

   @Override

   public void add(Edge<I, E> edge) {

     neighborIds.addW(edge.getTargetVertexId());

     neighborEdgeValues.addW(edge.getValue());

   }

   /**

    * 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 (neighborIds.capacity() > 4 * neighborIds.size()) {

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

       neighborEdgeValues.setCapacity(neighborIds.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 tmpId = neighborIds.getElementTypeOps().create();

     E tmpValue = neighborEdgeValues.getElementTypeOps().create();

     neighborIds.popIntoW(tmpId);

     neighborEdgeValues.popIntoW(tmpValue);

     if (i != neighborIds.size()) {

       neighborIds.setW(i, tmpId);

       neighborEdgeValues.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 tmpId = neighborIds.getElementTypeOps().create();

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

       neighborIds.getIntoW(i, tmpId);

       if (tmpId.equals(targetVertexId)) {

         removeAt(i);

       }

     }

   }

   @Override

   public int size() {

     return neighborIds.size();

   }

   @Override

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

     // Returns an iterator that reuses objects.

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

       private int index;

       /** Representative edge object. */

       private final Edge<I, E> representativeEdge = EdgeFactory.create(

           neighborIds.getElementTypeOps().create(),

           neighborEdgeValues.getElementTypeOps().create());

       @Override

       public boolean hasNext() {

         return index < neighborIds.size();

       }

       @Override

       public Edge<I, E> next() {

         if (!hasNext()) {

           throw new NoSuchElementException();

         }

         neighborIds.getIntoW(index, representativeEdge.getTargetVertexId());

         neighborEdgeValues.getIntoW(index, representativeEdge.getValue());

         index++;

         return representativeEdge;

       }

     };

   }

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

   private class ArrayMutableEdge extends DefaultEdge<I, E> {

     /** Index of the edge in the backing arrays. */

     private int index;

     /** Constructor. */

     public ArrayMutableEdge() {

       super(

           neighborIds.getElementTypeOps().create(),

           neighborEdgeValues.getElementTypeOps().create());

     }

     /**

      * Make the edge point to the given index in the backing arrays.

      *

      * @param index Index in the arrays

      */

     public void setIndex(int index) {

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

       neighborIds.getIntoW(index, getTargetVertexId());

       neighborEdgeValues.getIntoW(index, getValue());

       // Update the index.

       this.index = index;

     }

     @Override

     public void setValue(E value) {

       // Update the value object from the superclass.

       neighborEdgeValues.getElementTypeOps().set(getValue(), value);

       // Update the value stored in the backing array.

       neighborEdgeValues.setW(index, value);

     }

   }

   @Override

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

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

       /** Current position in the array. */

       private int index = 0;

       /** Representative edge object. */

       private final ArrayMutableEdge representativeEdge =

           new ArrayMutableEdge();

       @Override

       public boolean hasNext() {

         return index < neighborIds.size();

       }

       @Override

       public MutableEdge<I, E> next() {

         if (!hasNext()) {

           throw new NoSuchElementException();

         }

         representativeEdge.setIndex(index++);

         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(--index);

       }

     };

   }

   @Override

   public void write(DataOutput out) throws IOException {

     neighborIds.write(out);

     neighborEdgeValues.write(out);

   }

   @Override

   public void readFields(DataInput in) throws IOException {

     neighborIds.readFields(in);

     neighborEdgeValues.readFields(in);

   }

 }