ClickHouse/src/Functions/IFunctionCustomWeek.h

#pragma once
#include <DataTypes/DataTypeDate.h>
#include <DataTypes/DataTypeDate32.h>
#include <DataTypes/DataTypeDateTime.h>
#include <DataTypes/DataTypeDateTime64.h>
#include <Functions/CustomWeekTransforms.h>
#include <Functions/IFunction.h>
#include <Functions/TransformDateTime64.h>
#include <IO/WriteHelpers.h>
#include <Interpreters/Context.h>

namespace DB
{

namespace ErrorCodes
{
    extern const int ILLEGAL_TYPE_OF_ARGUMENT;
    extern const int NUMBER_OF_ARGUMENTS_DOESNT_MATCH;
}

template <typename Transform>
class IFunctionCustomWeek : public IFunction
{
public:
    bool isVariadic() const override { return true; }
    bool isSuitableForShortCircuitArgumentsExecution(const DataTypesWithConstInfo & /*arguments*/) const override { return true; }
    size_t getNumberOfArguments() const override { return 0; }
    bool useDefaultImplementationForConstants() const override { return true; }
    ColumnNumbers getArgumentsThatAreAlwaysConstant() const override { return {1, 2}; }

    bool hasInformationAboutMonotonicity() const override { return true; }

    Monotonicity getMonotonicityForRange(const IDataType & type, const Field & left, const Field & right) const override
    {
        if constexpr (std::is_same_v<typename Transform::FactorTransform, ZeroTransform>)
            return {.is_monotonic = true, .is_always_monotonic = true};

        const IFunction::Monotonicity is_monotonic = {.is_monotonic = true};
        const IFunction::Monotonicity is_not_monotonic;

        /// This method is called only if the function has one argument. Therefore, we do not care about the non-local time zone.
        const DateLUTImpl & date_lut = DateLUT::instance();

        if (left.isNull() || right.isNull())
            return {};

        /// The function is monotonous on the [left, right] segment, if the factor transformation returns the same values for them.

        if (checkAndGetDataType<DataTypeDate>(&type))
        {
            return Transform::FactorTransform::execute(UInt16(left.get<UInt64>()), date_lut)
                    == Transform::FactorTransform::execute(UInt16(right.get<UInt64>()), date_lut)
                ? is_monotonic
                : is_not_monotonic;
        }
        else
        {
            return Transform::FactorTransform::execute(UInt32(left.get<UInt64>()), date_lut)
                    == Transform::FactorTransform::execute(UInt32(right.get<UInt64>()), date_lut)
                ? is_monotonic
                : is_not_monotonic;
        }
    }

};

}