/*

  * 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.graph;

 import org.apache.hadoop.io.Writable;

 import org.apache.hadoop.io.WritableComparable;

 /**

  * Handles all the situations that can arise upon creation/removal of

  * vertices and edges.

  *

  * @param <I> Vertex id

  * @param <V> Vertex data

  * @param <E> Edge data

  */

 @SuppressWarnings("rawtypes")

 public interface VertexResolver<I extends WritableComparable,

     V extends Writable, E extends Writable> {

   /**

    * A vertex may have been removed, created zero or more times and had

    * zero or more messages sent to it.  This method will handle all situations

    * excluding the normal case (a vertex already exists and has zero or more

    * messages sent it to).

    *

    * @param vertexId Vertex id (can be used for {@link Vertex}'s initialize())

    * @param vertex Original vertex or null if none

    * @param vertexChanges Changes that happened to this vertex or null if none

    * @param hasMessages True iff vertex received messages in the last superstep

    * @return Vertex to be returned, if null, and a vertex currently exists

    *         it will be removed

    */

   Vertex<I, V, E> resolve(I vertexId,

       Vertex<I, V, E> vertex,

       VertexChanges<I, V, E> vertexChanges,

       boolean hasMessages);

 }