/**
 * 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.hadoop.hive.ql.optimizer;

import java.util.Collection;
import java.util.EnumSet;
import java.util.Stack;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.apache.hadoop.hive.conf.HiveConf;
import org.apache.hadoop.hive.ql.exec.Operator;
import org.apache.hadoop.hive.ql.exec.ReduceSinkOperator;
import org.apache.hadoop.hive.ql.exec.Utilities;
import org.apache.hadoop.hive.ql.lib.Node;
import org.apache.hadoop.hive.ql.lib.NodeProcessor;
import org.apache.hadoop.hive.ql.lib.NodeProcessorCtx;
import org.apache.hadoop.hive.ql.optimizer.stats.annotation.StatsRulesProcFactory;
import org.apache.hadoop.hive.ql.parse.OptimizeTezProcContext;
import org.apache.hadoop.hive.ql.parse.SemanticException;
import org.apache.hadoop.hive.ql.plan.ExprNodeDesc.ExprNodeDescEqualityWrapper;
import org.apache.hadoop.hive.ql.plan.OperatorDesc;
import org.apache.hadoop.hive.ql.plan.ReduceSinkDesc;
import org.apache.hadoop.hive.ql.stats.StatsUtils;

import static org.apache.hadoop.hive.ql.plan.ReduceSinkDesc.ReducerTraits.AUTOPARALLEL;
import static org.apache.hadoop.hive.ql.plan.ReduceSinkDesc.ReducerTraits.UNIFORM;
import static org.apache.hadoop.hive.ql.plan.ReduceSinkDesc.ReducerTraits.FIXED;

/**
 * SetReducerParallelism determines how many reducers should
 * be run for a given reduce sink.
 */
public class SetReducerParallelism implements NodeProcessor {

  private static final Logger LOG = LoggerFactory.getLogger(SetReducerParallelism.class.getName());

  @SuppressWarnings("unchecked")
  @Override
  public Object process(Node nd, Stack<Node> stack,
      NodeProcessorCtx procContext, Object... nodeOutputs)
      throws SemanticException {

    OptimizeTezProcContext context = (OptimizeTezProcContext) procContext;

    ReduceSinkOperator sink = (ReduceSinkOperator) nd;
    ReduceSinkDesc desc = sink.getConf();

    long bytesPerReducer = context.conf.getLongVar(HiveConf.ConfVars.BYTESPERREDUCER);
    int maxReducers = context.conf.getIntVar(HiveConf.ConfVars.MAXREDUCERS);
    int constantReducers = context.conf.getIntVar(HiveConf.ConfVars.HADOOPNUMREDUCERS);

    if (context.visitedReduceSinks.contains(sink)) {
      // skip walking the children
      LOG.debug("Already processed reduce sink: " + sink.getName());
      return true;
    }

    context.visitedReduceSinks.add(sink);

    if (desc.getNumReducers() <= 0) {
      if (constantReducers > 0) {
        LOG.info("Parallelism for reduce sink "+sink+" set by user to "+constantReducers);
        desc.setNumReducers(constantReducers);
      } else {
        long numberOfBytes = 0;

        // we need to add up all the estimates from the siblings of this reduce sink
        for (Operator<? extends OperatorDesc> sibling:
          sink.getChildOperators().get(0).getParentOperators()) {
          if (sibling.getStatistics() != null) {
            numberOfBytes = StatsUtils.safeAdd(
                numberOfBytes, sibling.getStatistics().getDataSize());
          } else {
            LOG.warn("No stats available from: "+sibling);
          }
        }

        int numReducers = Utilities.estimateReducers(numberOfBytes, bytesPerReducer,
            maxReducers, false);
        LOG.info("Set parallelism for reduce sink "+sink+" to: "+numReducers);
        desc.setNumReducers(numReducers);

        final Collection<ExprNodeDescEqualityWrapper> keyCols = ExprNodeDescEqualityWrapper.transform(desc.getKeyCols());
        final Collection<ExprNodeDescEqualityWrapper> partCols = ExprNodeDescEqualityWrapper.transform(desc.getPartitionCols());
        if (keyCols != null && keyCols.equals(partCols)) {
          desc.setReducerTraits(EnumSet.of(UNIFORM, AUTOPARALLEL));
        } else {
          desc.setReducerTraits(EnumSet.of(AUTOPARALLEL));
        }
      }
    } else {
      LOG.info("Number of reducers determined to be: "+desc.getNumReducers());
      desc.setReducerTraits(EnumSet.of(FIXED)); // usually controlled by bucketing
    }

    return false;
  }

}