/*
    * 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.block_app.reducers.collect;
  
  import org.apache.giraph.block_app.framework.api.BlockMasterApi;
  import org.apache.giraph.block_app.framework.api.CreateReducersApi;
  import org.apache.giraph.block_app.framework.piece.global_comm.BroadcastHandle;
  import org.apache.giraph.block_app.framework.piece.global_comm.ReducerHandle;
  import org.apache.giraph.block_app.framework.piece.global_comm.array.BroadcastArrayHandle;
  import org.apache.giraph.block_app.reducers.array.ArrayOfHandles;
  import org.apache.giraph.function.Supplier;
  import org.apache.giraph.master.MasterGlobalCommUsage;
  import org.apache.giraph.reducers.ReduceOperation;
  import org.apache.giraph.worker.WorkerBroadcastUsage;
  import org.apache.giraph.writable.kryo.KryoWritableWrapper;
  import org.apache.giraph.writable.kryo.TransientRandom;
  
  /**
   * Reducing values into a list of reducers, randomly,
   * and getting the results of all reducers together
   *
   * @param <S> Single value type
   * @param <R> Reduced value type
   */
  public abstract class ShardedReducerHandle<S, R>
      implements ReducerHandle<S, R> {
    // Use a prime number for number of reducers, large enough to make sure
    // request sizes are within expected size (0.5MB)
    protected static final int REDUCER_COUNT = 39989;
  
    protected final TransientRandom random = new TransientRandom();
  
    protected ArrayOfHandles.ArrayOfReducers<S, KryoWritableWrapper<R>> reducers;
  
    public final void register(final CreateReducersApi reduceApi) {
      reducers = new ArrayOfHandles.ArrayOfReducers<>(REDUCER_COUNT,
          new Supplier<ReducerHandle<S, KryoWritableWrapper<R>>>() {
            @Override
            public ReducerHandle<S, KryoWritableWrapper<R>> get() {
              return reduceApi.createLocalReducer(createReduceOperation());
            }
          });
    }
  
    @Override
    public final void reduce(S value) {
      reducers.get(random.nextInt(REDUCER_COUNT)).reduce(value);
    }
  
    @Override
    public final R getReducedValue(MasterGlobalCommUsage master) {
      KryoWritableWrapper<R> ret = new KryoWritableWrapper<>(
          createReduceResult(master));
      ReduceOperation<S, KryoWritableWrapper<R>> reduceOperation =
          createReduceOperation();
      for (int i = 0; i < REDUCER_COUNT; i++) {
        reduceOperation.reduceMerge(ret,
            reducers.get(i).getReducedValue(master));
      }
      return ret.get();
    }
  
    public abstract ReduceOperation<S, KryoWritableWrapper<R>>
    createReduceOperation();
  
    public R createReduceResult(MasterGlobalCommUsage master) {
      return createReduceOperation().createInitialValue().get();
    }
  
    public BroadcastHandle<R> createBroadcastHandle(
        BroadcastArrayHandle<KryoWritableWrapper<R>> broadcasts) {
      return new ShardedBroadcastHandle(broadcasts);
    }
  
    @Override
    public final BroadcastHandle<R> broadcastValue(BlockMasterApi masterApi) {
      return createBroadcastHandle(reducers.broadcastValue(masterApi));
    }
  
    /**
     * Broadcast for ShardedReducerHandle
     */
    public class ShardedBroadcastHandle implements BroadcastHandle<R> {
      protected final BroadcastArrayHandle<KryoWritableWrapper<R>> broadcasts;
 
     public ShardedBroadcastHandle(
         BroadcastArrayHandle<KryoWritableWrapper<R>> broadcasts) {
       this.broadcasts = broadcasts;
     }
 
     public R createBroadcastResult(WorkerBroadcastUsage worker) {
       return createReduceOperation().createInitialValue().get();
     }
 
     @Override
     public final R getBroadcast(WorkerBroadcastUsage worker) {
       KryoWritableWrapper<R> ret = new KryoWritableWrapper<>(
           createBroadcastResult(worker));
       ReduceOperation<S, KryoWritableWrapper<R>> reduceOperation =
           createReduceOperation();
       for (int i = 0; i < REDUCER_COUNT; i++) {
         reduceOperation.reduceMerge(ret,
             broadcasts.get(i).getBroadcast(worker));
       }
       return ret.get();
     }
   }
 }