/*
 * 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.phoenix.expression.aggregator;

import java.util.*;
import java.util.Map.Entry;
import org.apache.hadoop.hbase.io.ImmutableBytesWritable;
import org.apache.phoenix.expression.*;
import org.apache.phoenix.schema.SortOrder;
import org.apache.phoenix.schema.tuple.Tuple;
import org.apache.phoenix.schema.types.PDataType;
import org.apache.phoenix.schema.types.PDecimal;

/**
 * Built-in function for
 * {@code PERCENTILE_DISC(<expression>) WITHIN GROUP (ORDER BY <expression> ASC/DESC) } aggregate
 * function
 * @since 1.2.1
 */
public class PercentileDiscClientAggregator extends DistinctValueWithCountClientAggregator {

  private final List<Expression> exps;
  ColumnExpression columnExp = null;

  public PercentileDiscClientAggregator(List<Expression> exps, SortOrder sortOrder) {
    super(sortOrder);
    this.exps = exps;
  }

  @Override
  public boolean evaluate(Tuple tuple, ImmutableBytesWritable ptr) {
    // Reset buffer so that it gets initialized with the current datatype of the column
    buffer = null;
    if (cachedResult == null) {
      columnExp = (ColumnExpression) exps.get(0);
      // Second exp will be a LiteralExpression of Boolean type indicating
      // whether the ordering to be ASC/DESC
      LiteralExpression isAscendingExpression = (LiteralExpression) exps.get(1);
      boolean isAscending = (Boolean) isAscendingExpression.getValue();

      // Third expression will be LiteralExpression
      LiteralExpression percentileExp = (LiteralExpression) exps.get(2);
      float p = ((Number) percentileExp.getValue()).floatValue();
      Map<Object, Integer> sorted = getSortedValueVsCount(isAscending, columnExp.getDataType());
      int currValue = 0;
      Object result = null;
      // Here the Percentile_disc returns the cum_dist() that is greater or equal to the
      // Percentile (p) specified in the query. So the result set will be of that of the
      // datatype of the column being selected
      for (Entry<Object, Integer> entry : sorted.entrySet()) {
        result = entry.getKey();
        Integer value = entry.getValue();
        currValue += value;
        float cum_dist = (float) currValue / (float) totalCount;
        if (cum_dist >= p) {
          break;
        }
      }
      this.cachedResult = result;
    }
    if (buffer == null) {
      // Initialize based on the datatype
      // columnExp cannot be null
      buffer = new byte[columnExp.getDataType().getByteSize()];
    }
    // Copy the result to the buffer.
    System.arraycopy(columnExp.getDataType().toBytes(this.cachedResult), 0, buffer, 0,
      buffer.length);
    ptr.set(buffer);
    return true;
  }

  @Override
  protected int getBufferLength() {
    // Will be used in the aggregate() call
    return PDecimal.INSTANCE.getByteSize();
  }

  @Override
  protected PDataType getResultDataType() {
    return columnExp.getDataType();
  }

}
