/*

  * 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.utils;

 import com.google.common.collect.ComparisonChain;

 import org.apache.giraph.edge.Edge;

 import org.apache.hadoop.io.WritableComparable;

 import java.io.Serializable;

 import java.util.Comparator;

 /**

  * Comparator for edges.

  *

  * @param <I> Vertex id

  * @param <E> Edge value (needs to be WritableComparable)

  */

 public class EdgeComparator<I extends WritableComparable,

     E extends WritableComparable> implements Comparator<Edge<I, E>>,

     Serializable {

   /** Serialization version. */

   private static final long serialVersionUID = 1L;

   @Override

   public int compare(Edge<I, E> e1, Edge<I, E> e2) {

     return compareEdges(e1, e2);

   }

   /**

    * Compares two edges.

    *

    * @param e1 First edge

    * @param e2 Second edge

    * @param <I> Vertex id

    * @param <E> Edge value (needs to be WritableComparable)

    * @return A negative, zero, or positive value depending

    */

   public static <I extends WritableComparable, E extends WritableComparable>

   int compareEdges(Edge<I, E> e1, Edge<I, E> e2) {

     return ComparisonChain.start()

         .compare(e1.getTargetVertexId(), e2.getTargetVertexId())

         .compare(e1.getValue(), e2.getValue())

         .result();

   }

   /**

    * Indicates whether two edges are equal.

    *

    * @param e1 First edge

    * @param e2 Second edge

    * @param <I> Vertex id

    * @param <E> Edge value (needs to be WritableComparable)

    * @return Whether the two edges are equal

    */

   public static <I extends WritableComparable, E extends WritableComparable>

   boolean equal(Edge<I, E> e1, Edge<I, E> e2) {

     return compareEdges(e1, e2) == 0;

   }

 }