ClickHouse/src/Functions/FunctionDateOrDateTimeToDateOrDate32.h

#pragma once
#include <Functions/IFunctionDateOrDateTime.h>

namespace DB
{

namespace ErrorCodes
{
    extern const int ILLEGAL_TYPE_OF_ARGUMENT;
}

template <typename Transform>
class FunctionDateOrDateTimeToDateOrDate32 : public IFunctionDateOrDateTime<Transform>, WithContext
{
public:
    bool enable_date32_results = false;

    static FunctionPtr create(ContextPtr context_)
    {
        return std::make_shared<FunctionDateOrDateTimeToDateOrDate32>(context_);
    }

    explicit FunctionDateOrDateTimeToDateOrDate32(ContextPtr context_) : WithContext(context_)
    {
        enable_date32_results = context_->getSettingsRef().enable_date32_results;
    }

    DataTypePtr getReturnTypeImpl(const ColumnsWithTypeAndName & arguments) const override
    {
        this->checkArguments(arguments, true);

        const IDataType * from_type = arguments[0].type.get();
        WhichDataType which(from_type);

        /// If the time zone is specified but empty, throw an exception.
        if (which.isDateTime() || which.isDateTime64())
        {
            std::string time_zone = extractTimeZoneNameFromFunctionArguments(arguments, 1, 0);
            /// only validate the time_zone part if the number of arguments is 2.
            if (arguments.size() == 2 && time_zone.empty())
                throw Exception(
                    "Function " + this->getName() + " supports a 2nd argument (optional) that must be non-empty and be a valid time zone",
                    ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
            if (which.isDateTime64() && enable_date32_results)
                return std::make_shared<DataTypeDate32>();
            else
                return std::make_shared<DataTypeDate>();
        }
        if (which.isDate32() && enable_date32_results)
            return std::make_shared<DataTypeDate32>();
        else
            return std::make_shared<DataTypeDate>();
    }

    ColumnPtr executeImpl(const ColumnsWithTypeAndName & arguments, const DataTypePtr & result_type, size_t input_rows_count) const override
    {
        const IDataType * from_type = arguments[0].type.get();
        WhichDataType which(from_type);

        if (which.isDate())
            return DateTimeTransformImpl<DataTypeDate, DataTypeDate, Transform>::execute(arguments, result_type, input_rows_count);
        else if (which.isDate32())
            if (enable_date32_results)
                return DateTimeTransformImpl<DataTypeDate32, DataTypeDate32, Transform, true>::execute(arguments, result_type, input_rows_count);
            else
                return DateTimeTransformImpl<DataTypeDate32, DataTypeDate, Transform>::execute(arguments, result_type, input_rows_count);
        else if (which.isDateTime())
            return DateTimeTransformImpl<DataTypeDateTime, DataTypeDate, Transform>::execute(arguments, result_type, input_rows_count);
        else if (which.isDateTime64())
        {
            const auto scale = static_cast<const DataTypeDateTime64 *>(from_type)->getScale();

            const TransformDateTime64<Transform> transformer(scale);
            if (enable_date32_results)
                return DateTimeTransformImpl<DataTypeDateTime64, DataTypeDate32, decltype(transformer), true>::execute(arguments, result_type, input_rows_count, transformer);
            else
                return DateTimeTransformImpl<DataTypeDateTime64, DataTypeDate, decltype(transformer)>::execute(arguments, result_type, input_rows_count, transformer);
        }
        else
            throw Exception("Illegal type " + arguments[0].type->getName() + " of argument of function " + this->getName(),
                ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
    }

};

}