/*
    * 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.master.input;
  
  import org.apache.giraph.worker.WorkerInfo;
  import org.apache.hadoop.mapreduce.InputSplit;
  
  import java.io.IOException;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  import java.util.concurrent.ConcurrentLinkedQueue;
  import java.util.concurrent.atomic.AtomicBoolean;
  import java.util.concurrent.atomic.AtomicInteger;
  
  /**
   * Input splits organizer for vertex and edge input splits on master, which
   * uses locality information
   */
  public class LocalityAwareInputSplitsMasterOrganizer
      implements InputSplitsMasterOrganizer {
    /** All splits before this pointer were taken */
    private final AtomicInteger listPointer = new AtomicInteger();
    /** List of serialized splits */
    private final List<byte[]> serializedSplits;
    /** Array containing information about whether a split was taken or not */
    private final AtomicBoolean[] splitsTaken;
  
    /** Map with preferred splits for each worker */
    private final Map<Integer, ConcurrentLinkedQueue<Integer>>
        workerToPreferredSplitsMap;
  
  
    /**
     * Constructor
     *
     * @param serializedSplits Serialized splits
     * @param splits           Splits
     * @param workers          List of workers
     */
    public LocalityAwareInputSplitsMasterOrganizer(List<byte[]> serializedSplits,
        List<InputSplit> splits, List<WorkerInfo> workers) {
      this.serializedSplits = serializedSplits;
      splitsTaken = new AtomicBoolean[serializedSplits.size()];
      // Mark all splits as not taken initially
      for (int i = 0; i < serializedSplits.size(); i++) {
        splitsTaken[i] = new AtomicBoolean(false);
      }
  
      workerToPreferredSplitsMap = new HashMap<>();
      for (WorkerInfo worker : workers) {
        workerToPreferredSplitsMap.put(worker.getTaskId(),
            new ConcurrentLinkedQueue<Integer>());
      }
      // Go through all splits
      for (int i = 0; i < splits.size(); i++) {
        try {
          String[] locations = splits.get(i).getLocations();
          // For every worker
          for (WorkerInfo worker : workers) {
            // Check splits locations
            for (String location : locations) {
              // If split is local for the worker, add it to preferred list
              if (location.contains(worker.getHostname())) {
                workerToPreferredSplitsMap.get(worker.getTaskId()).add(i);
                break;
              }
            }
          }
        } catch (IOException | InterruptedException e) {
          throw new IllegalStateException(
              "Exception occurred while getting splits locations", e);
        }
      }
    }
  
    @Override
    public byte[] getSerializedSplitFor(int workerTaskId) {
      ConcurrentLinkedQueue<Integer> preferredSplits =
          workerToPreferredSplitsMap.get(workerTaskId);
      // Try to find a local split
      while (true) {
        // Get position to check
       Integer splitIndex = preferredSplits.poll();
       // Check if all local splits were already processed for this worker
       if (splitIndex == null) {
         break;
       }
       // Try to reserve the split
       if (splitsTaken[splitIndex].compareAndSet(false, true)) {
         return serializedSplits.get(splitIndex);
       }
     }
 
     // No more local splits available, proceed linearly from splits list
     while (true) {
       // Get position to check
       int splitIndex = listPointer.getAndIncrement();
       // Check if all splits were already taken
       if (splitIndex >= serializedSplits.size()) {
         return null;
       }
       // Try to reserve the split
       if (splitsTaken[splitIndex].compareAndSet(false, true)) {
         return serializedSplits.get(splitIndex);
       }
     }
   }
 }