/*

  * 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.examples.scc;

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

 import java.io.DataInput;

 import java.io.DataOutput;

 import java.io.IOException;

 import org.apache.hadoop.io.Writable;

 /**

  * Vertex value for the Strongly Connected Components algorithm. It keeps track

  * of the parents of the vertex in order to traverse the graph backwards.

  */

 public class SccVertexValue implements Writable {

   /** Vertex's parents **/

   private LongArrayList parents;

   /** Current vertex value **/

   private long value = Long.MIN_VALUE;

   /** Indicates whether the vertex was trimmed, hence,

    * it can't be part of the computation anymore.

    */

   private boolean active = true;

   /**

    * Public constructor required for serialization.

    */

   public SccVertexValue() {

   }

   /**

    * Constructor

    * @param value Initial value for this vertex.

    */

   public SccVertexValue(long value) {

     this.value = value;

   }

   @Override

   public void readFields(DataInput in) throws IOException {

     value = in.readLong();

     int size = in.readInt();

     if (size != 0) {

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

         addParent(in.readLong());

       }

     }

     active = in.readBoolean();

   }

   @Override

   public void write(DataOutput out) throws IOException {

     out.writeLong(value);

     int size = parents == null ? 0 : parents.size();

     out.writeInt(size);

     if (size != 0) {

       for (long incomingId : parents) {

         out.writeLong(incomingId);

       }

     }

     out.writeBoolean(active);

   }

   /**

    * Returns the list of parent vertices, i.e., vertices that are at the other

    * end of incoming edges. If the vertex doesn't have any incoming edge, it

    * returns null.

    * @return List of the vertex's parents.

    */

   public LongArrayList getParents() {

     return parents;

   }

   /**

    * Adds a vertex id to the list of parent vertices.

    * @param vertexId It of the parent vertex.

    */

   public void addParent(long vertexId) {

     // Initialize the list of parent vertices only when one attempts to add

     // the first item, so we save some memory on vertices that have no incoming

     // edges

     if (parents == null) {

       parents = new LongArrayList();

     }

     parents.add(vertexId);

   }

   /**

    * Clear parents list.

    */

   public void clearParents() {

     parents = null;

   }

   /**

    * Sets the vertex value. At the end of the SCC computation, vertices with the

    * same vertex value are part of the same component.

    * @param value Vertex value.

    */

   public void set(long value) {

     this.value = value;

   }

   /**

    * Returns the vertex value. At the end of the SCC computation, vertices with

    * the same vertex value are part of the same component.

    * @return Current vertex value.

    */

   public long get() {

     return value;

   }

   /**

    * Remove this vertex from the computation.

    */

   public void deactivate() {

     this.active = false;

   }

   /**

    * Indicates whether the vertex was removed in a Trimming phase.

    * @return True if the vertex was trimmed, otherwise, return false.

    */

   public boolean isActive() {

     return active;

   }

   @Override

   public String toString() {

     return String.valueOf(value);

   }

 }