/*

  * 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 org.apache.giraph.conf.ImmutableClassesGiraphConfiguration;

 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;

 /**

  * Helper class that wraps the current out-edges and inserts them into a new

  * data structure as they are iterated over.

  * Used by Vertex to provide a mutable iterator when the chosen

  * {@link OutEdges} doesn't offer a specialized one.

  * The edges are "unwrapped" back to the chosen {@link OutEdges} data

  * structure as soon as possible: either when the iterator is exhausted,

  * or after compute() if iteration has been terminated early.

  *

  * @param <I> Vertex id

  * @param <E> Edge value

  */

 public class MutableEdgesWrapper<I extends WritableComparable,

     E extends Writable> implements OutEdges<I, E> {

   /** New edges data structure (initially empty). */

   private final OutEdges<I, E> newEdges;

   /** Iterator over the old edges. */

   private final Iterator<Edge<I, E>> oldEdgesIterator;

   /** Last edge that was returned during iteration. */

   private MutableEdge<I, E> currentEdge;

   /** Number of edges. */

   private int numEdges;

   /**

    * Private constructor: instantiation happens through the {@code wrap()}

    * factory method.

    *

    * @param oldEdges Current out-edges

    * @param newEdges New (empty) edges data structure

    */

   private MutableEdgesWrapper(OutEdges<I, E> oldEdges,

                               OutEdges<I, E> newEdges) {

     oldEdgesIterator = oldEdges.iterator();

     this.newEdges = newEdges;

     numEdges = oldEdges.size();

   }

   /**

    * Factory method to create a new wrapper over the existing out-edges.

    *

    * @param edges Current out-edges

    * @param conf Configuration

    * @param <I> Vertex id

    * @param <E> Edge value

    * @return The wrapped edges

    */

   public static <I extends WritableComparable, E extends Writable>

   MutableEdgesWrapper<I, E> wrap(

       OutEdges<I, E> edges,

       ImmutableClassesGiraphConfiguration<I, ?, E> conf) {

     MutableEdgesWrapper<I, E> wrapper = new MutableEdgesWrapper<I, E>(

         edges, conf.createAndInitializeOutEdges(edges.size()));

     return wrapper;

   }

   /**

    * Moves all the remaining edges to the new data structure, and returns it.

    *

    * @return The new {@link OutEdges} data structure.

    */

   public OutEdges<I, E> unwrap() {

     if (currentEdge != null) {

       newEdges.add(currentEdge);

       currentEdge = null;

     }

     while (oldEdgesIterator.hasNext()) {

       newEdges.add(oldEdgesIterator.next());

     }

     return newEdges;

   }

   /**

    * Get the new {@link OutEdges} data structure.

    *

    * @return New edges

    */

   public OutEdges<I, E> getNewEdges() {

     return newEdges;

   }

   /**

    * Get the iterator over the old edges data structure.

    *

    * @return Old edges iterator

    */

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

     return oldEdgesIterator;

   }

   /**

    * Get the last edge returned by the mutable iterator.

    *

    * @return Last edge iterated on

    */

   public MutableEdge<I, E> getCurrentEdge() {

     return currentEdge;

   }

   /**

    * Set the last edge returned by the mutable iterator.

    *

    * @param edge Last edge iterated on

    */

   public void setCurrentEdge(MutableEdge<I, E> edge) {

     currentEdge = edge;

   }

   /**

    * Decrement the number of edges (to account for a deletion from the mutable

    * iterator).

    */

   public void decrementEdges() {

     --numEdges;

   }

   @Override

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

     throw new IllegalStateException("initialize: MutableEdgesWrapper should " +

         "never be initialized.");

   }

   @Override

   public void initialize(int capacity) {

     throw new IllegalStateException("initialize: MutableEdgesWrapper should " +

         "never be initialized.");

   }

   @Override

   public void initialize() {

     throw new IllegalStateException("initialize: MutableEdgesWrapper should " +

         "never be initialized.");

   }

   @Override

   public void add(Edge<I, E> edge) {

     unwrap().add(edge);

   }

   @Override

   public void remove(I targetVertexId) {

     unwrap().remove(targetVertexId);

   }

   @Override

   public int size() {

     return numEdges;

   }

   @Override

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

     return unwrap().iterator();

   }

   @Override

   public void write(DataOutput out) throws IOException {

     throw new IllegalStateException("write: MutableEdgesWrapper should " +

         "never be serialized.");

   }

   @Override

   public void readFields(DataInput in) throws IOException {

     throw new IllegalStateException("readFields: MutableEdgesWrapper should " +

         "never be deserialized.");

   }

 }