code: /*
   * 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.skywalking.oap.query.graphql.mqe.rt.operation;
  
  import com.google.common.collect.Streams;
  import java.util.ArrayList;
  import java.util.Comparator;
  import java.util.List;
  import java.util.Optional;
  import java.util.OptionalDouble;
  import java.util.function.Function;
  import java.util.stream.DoubleStream;
  import org.apache.skywalking.mqe.rt.grammar.MQEParser;
  import org.apache.skywalking.oap.query.graphql.mqe.rt.exception.IllegalExpressionException;
  import org.apache.skywalking.oap.query.graphql.type.mql.ExpressionResult;
  import org.apache.skywalking.oap.query.graphql.type.mql.ExpressionResultType;
  import org.apache.skywalking.oap.query.graphql.type.mql.MQEValue;
  import org.apache.skywalking.oap.query.graphql.type.mql.MQEValues;
  
  public class AggregationOp {
      public static ExpressionResult doAggregationOp(ExpressionResult result,
                                                     int opType) throws IllegalExpressionException {
          switch (opType) {
              case MQEParser.AVG:
                  return aggregateResult(result, mqeValues -> mqeValues.getValues()
                                                                       .stream()
                                                                       .filter(mqeValue -> !mqeValue.isEmptyValue())
                                                                       .flatMapToDouble(mqeValue -> DoubleStream.of(
                                                                           mqeValue.getDoubleValue()))
                                                                       .average());
              case MQEParser.COUNT:
                  return aggregateResult(result, mqeValues -> OptionalDouble.of(
                      mqeValues.getValues().stream().filter(mqeValue -> !mqeValue.isEmptyValue()).count()));
              case MQEParser.LATEST:
                  if (result.getType() != ExpressionResultType.TIME_SERIES_VALUES) {
                      throw new IllegalExpressionException("LATEST can only be used in time series result.");
                  }
                  return selectResult(result, mqeValues -> Streams.findLast(mqeValues.getValues()
                                                                                     .stream()
                                                                                     .filter(mqeValue -> !mqeValue.isEmptyValue())));
              case MQEParser.MAX:
                  return selectResult(result, mqeValues -> mqeValues.getValues()
                                                                    .stream()
                                                                    .filter(mqeValue -> !mqeValue.isEmptyValue())
                                                                    .max(Comparator.comparingDouble(
                                                                        MQEValue::getDoubleValue)));
              case MQEParser.MIN:
                  return selectResult(result, mqeValues -> mqeValues.getValues()
                                                                    .stream()
                                                                    .filter(mqeValue -> !mqeValue.isEmptyValue())
                                                                    .min(Comparator.comparingDouble(
                                                                        MQEValue::getDoubleValue)));
              case MQEParser.SUM:
                  return aggregateResult(result, mqeValues -> OptionalDouble.of(mqeValues.getValues()
                                                                                         .stream()
                                                                                         .filter(
                                                                                             mqeValue -> !mqeValue.isEmptyValue())
                                                                                         .flatMapToDouble(
                                                                                             mqeValue -> DoubleStream.of(
                                                                                                 mqeValue.getDoubleValue()))
                                                                                         .sum()));
              default:
                  throw new IllegalExpressionException("Unsupported aggregation operation.");
          }
      }
  
      private static ExpressionResult aggregateResult(ExpressionResult result,
                                                      Function<MQEValues, OptionalDouble> aggregator) {
          for (MQEValues resultValues : result.getResults()) {
              OptionalDouble resultValue = aggregator.apply(resultValues);
              List<MQEValue> mqeValueList = new ArrayList<>(1);
              //no id
              MQEValue mqeValue = new MQEValue();
              if (resultValue.isPresent()) {
                  mqeValue.setEmptyValue(false);
                  mqeValue.setDoubleValue(resultValue.getAsDouble());
              } else {
                  mqeValue.setEmptyValue(true);
              }
              mqeValueList.add(mqeValue);
              resultValues.setValues(mqeValueList);
          }
          result.setType(ExpressionResultType.SINGLE_VALUE);
          return result;
      }
  
      private static ExpressionResult selectResult(ExpressionResult result,
                                                   Function<MQEValues, Optional<MQEValue>> aggregator) {
          for (MQEValues resultValues : result.getResults()) {
              Optional<MQEValue> resultValue = aggregator.apply(resultValues);
              List<MQEValue> mqeValueList = new ArrayList<>(1);
              if (resultValue.isPresent()) {
                  mqeValueList.add(resultValue.get());
              } else {
                  MQEValue mqeValue = new MQEValue();
                  mqeValue.setEmptyValue(true);
                  mqeValueList.add(mqeValue);
              }
              resultValues.setValues(mqeValueList);
          }
          result.setType(ExpressionResultType.SINGLE_VALUE);
          return result;
      }
  }
  