content: /*
   * 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 com.alibaba.graphscope.example.giraph;
  
  import org.apache.hadoop.io.Writable;
  
  import java.io.DataInput;
  import java.io.DataOutput;
  import java.io.IOException;
  import java.util.ArrayList;
  
  /**
   * 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 ArrayList<Long> 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 ArrayList<Long> 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 ArrayList<>(10);
          }
          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);
      }
  }
  