ClickHouse/dbms/src/AggregateFunctions/AggregateFunctionArgMinMax.h

#pragma once

#include <AggregateFunctions/AggregateFunctionMinMaxAny.h>
#include <AggregateFunctions/IBinaryAggregateFunction.h>


namespace DB
{


/// For possible values for template parameters, see AggregateFunctionMinMaxAny.h
template <typename ResultData, typename ValueData>
struct AggregateFunctionArgMinMaxData
{
    using ResultData_t = ResultData;
    using ValueData_t = ValueData;

    ResultData result;  // the argument at which the minimum/maximum value is reached.
    ValueData value;    // value for which the minimum/maximum is calculated.
};

/// Returns the first arg value found for the minimum/maximum value. Example: argMax(arg, value).
template <typename Data>
class AggregateFunctionArgMinMax final : public IBinaryAggregateFunction<Data, AggregateFunctionArgMinMax<Data>>
{
private:
    DataTypePtr type_res;
    DataTypePtr type_val;

public:
    String getName() const override { return (0 == strcmp(Data::ValueData_t::name(), "min")) ? "argMin" : "argMax"; }

    DataTypePtr getReturnType() const override
    {
        return type_res;
    }

    void setArgumentsImpl(const DataTypes & arguments)
    {
        type_res = arguments[0];
        type_val = arguments[1];
    }

    void addImpl(AggregateDataPtr place, const IColumn & column_arg, const IColumn & column_max, size_t row_num, Arena *) const
    {
        if (this->data(place).value.changeIfBetter(column_max, row_num))
            this->data(place).result.change(column_arg, row_num);
    }

    void merge(AggregateDataPtr place, ConstAggregateDataPtr rhs, Arena * arena) const override
    {
        if (this->data(place).value.changeIfBetter(this->data(rhs).value))
            this->data(place).result.change(this->data(rhs).result);
    }

    void serialize(ConstAggregateDataPtr place, WriteBuffer & buf) const override
    {
        this->data(place).result.write(buf, *type_res.get());
        this->data(place).value.write(buf, *type_val.get());
    }

    void deserialize(AggregateDataPtr place, ReadBuffer & buf, Arena *) const override
    {
        this->data(place).result.read(buf, *type_res.get());
        this->data(place).value.read(buf, *type_val.get());
    }

    void insertResultInto(ConstAggregateDataPtr place, IColumn & to) const override
    {
        this->data(place).result.insertResultInto(to);
    }
};

}