/**
 * 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.exec.vector.expressions.aggregates;

import org.apache.hadoop.hive.ql.exec.Description;
import org.apache.hadoop.hive.ql.exec.vector.VectorAggregationBufferRow;
import org.apache.hadoop.hive.ql.exec.vector.VectorizedRowBatch;
import org.apache.hadoop.hive.ql.exec.vector.expressions.VectorExpression;
import org.apache.hadoop.hive.ql.metadata.HiveException;
import org.apache.hadoop.hive.ql.plan.AggregationDesc;
import org.apache.hadoop.hive.ql.util.JavaDataModel;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.primitive.PrimitiveObjectInspectorFactory;
import org.apache.hadoop.io.LongWritable;

/**
 * VectorUDAFCountStar. Vectorized implementation for COUNT(*) aggregates.
 */
@Description(name = "count", value = "_FUNC_(expr) - Returns count(*) (vectorized)")
public class VectorUDAFCountStar extends VectorAggregateExpression {

  private static final long serialVersionUID = 1L;

    /**
     * class for storing the current aggregate value.
     */
    static class Aggregation implements AggregationBuffer {

      private static final long serialVersionUID = 1L;

      transient private long count;

      @Override
      public int getVariableSize() {
        throw new UnsupportedOperationException();
      }

      @Override
      public void reset() {
        count = 0L;
      }
    }


    @Override
    public VectorExpression inputExpression() {
      // None.
      return null;
    }

    transient private final LongWritable result;

    public VectorUDAFCountStar(VectorExpression inputExpression) {
      this();
    }

    public VectorUDAFCountStar() {
      super();
      result = new LongWritable(0);
    }

    private Aggregation getCurrentAggregationBuffer(
        VectorAggregationBufferRow[] aggregationBufferSets,
        int aggregateIndex,
        int row) {
      VectorAggregationBufferRow mySet = aggregationBufferSets[row];
      Aggregation myagg = (Aggregation) mySet.getAggregationBuffer(aggregateIndex);
      return myagg;
    }

    @Override
    public void aggregateInputSelection(
      VectorAggregationBufferRow[] aggregationBufferSets,
      int aggregateIndex,
      VectorizedRowBatch batch) throws HiveException {

      int batchSize = batch.size;

      if (batchSize == 0) {
        return;
      }

      // count(*) cares not about NULLs nor selection
      for (int i=0; i < batchSize; ++i) {
        Aggregation myAgg = getCurrentAggregationBuffer(
            aggregationBufferSets, aggregateIndex, i);
        ++myAgg.count;
      }
    }

    @Override
    public void aggregateInput(AggregationBuffer agg, VectorizedRowBatch batch)
    throws HiveException {

      int batchSize = batch.size;

      if (batchSize == 0) {
        return;
      }

      Aggregation myagg = (Aggregation)agg;
      myagg.count += batchSize;
    }

    @Override
    public AggregationBuffer getNewAggregationBuffer() throws HiveException {
      return new Aggregation();
    }

    @Override
    public void reset(AggregationBuffer agg) throws HiveException {
      Aggregation myAgg = (Aggregation) agg;
      myAgg.reset();
    }

    @Override
    public Object evaluateOutput(AggregationBuffer agg) throws HiveException {
      Aggregation myagg = (Aggregation) agg;
      result.set (myagg.count);
      return result;
    }

    @Override
    public ObjectInspector getOutputObjectInspector() {
      return PrimitiveObjectInspectorFactory.writableLongObjectInspector;
    }

    @Override
    public long getAggregationBufferFixedSize() {
      JavaDataModel model = JavaDataModel.get();
      return JavaDataModel.alignUp(
        model.object() +
        model.primitive2() +
        model.primitive1(),
        model.memoryAlign());
    }

    @Override
    public void init(AggregationDesc desc) throws HiveException {
      // No-op
    }
}