/*
    * 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.io.formats;
  
  import org.apache.giraph.conf.ImmutableClassesGiraphConfiguration;
  import org.apache.giraph.partition.PartitionUtils;
  import org.apache.giraph.worker.WorkerInfo;
  
  import java.util.Collections;
  import java.util.List;
  import java.util.Random;
  
  /**
   * Helper class to generate pseudo-random local edges.
   * Like {@link PseudoRandomLocalEdgesHelper}, but for graphs where vertex ids
   * are integers.
   */
  public class PseudoRandomIntNullLocalEdgesHelper {
    /** Minimum ratio of partition-local edges. */
    private float minLocalEdgesRatio;
    /** Total number of vertices. */
    private int numVertices;
    /** Total number of partitions. */
    private int numPartitions;
    /** Average partition size. */
    private int partitionSize;
  
    /**
     * Constructor.
     *
     * @param numVertices        Total number of vertices.
     * @param conf               Configuration.
     */
    public PseudoRandomIntNullLocalEdgesHelper(int numVertices,
        ImmutableClassesGiraphConfiguration conf) {
      this.minLocalEdgesRatio = conf.getFloat(
          PseudoRandomInputFormatConstants.LOCAL_EDGES_MIN_RATIO,
          PseudoRandomInputFormatConstants.LOCAL_EDGES_MIN_RATIO_DEFAULT);
      this.numVertices = numVertices;
      int numWorkers = conf.getMaxWorkers();
      List<WorkerInfo> workerInfos = Collections.nCopies(numWorkers,
          new WorkerInfo());
      numPartitions = PartitionUtils.computePartitionCount(
          workerInfos.size(), conf);
      partitionSize = numVertices / numPartitions;
    }
  
    /**
     * Generate a destination vertex id for the given source vertex,
     * using the desired configuration for edge locality and the provided
     * pseudo-random generator.
     *
     * @param sourceVertexId Source vertex id.
     * @param rand           Pseudo-random generator.
     * @return Destination vertex id.
     */
    public int generateDestVertex(int sourceVertexId, Random rand) {
      if (rand.nextFloat() < minLocalEdgesRatio) {
        int partitionId = sourceVertexId % numPartitions;
        return partitionId + numPartitions * rand.nextInt(partitionSize);
      } else {
        return rand.nextInt(numVertices);
      }
    }
  }