#include <Functions/IFunction.h>
#include <Functions/FunctionFactory.h>
#include <DataTypes/DataTypesNumber.h>
#include <Columns/ColumnsNumber.h>
#include <DataTypes/DataTypeNullable.h>
#include <Core/Settings.h>
#include <Interpreters/Context.h>

namespace DB
{
namespace Setting
{
    extern const SettingsBool allow_experimental_analyzer;
}

namespace
{

/// Return true if the column is nullable.
class FunctionIsNullable : public IFunction
{
public:
    static constexpr auto name = "isNullable";
    static FunctionPtr create(ContextPtr context)
    {
        return std::make_shared<FunctionIsNullable>(context->getSettingsRef()[Setting::allow_experimental_analyzer]);
    }

    explicit FunctionIsNullable(bool use_analyzer_) : use_analyzer(use_analyzer_) {}

    String getName() const override
    {
        return name;
    }

    ColumnPtr getConstantResultForNonConstArguments(const ColumnsWithTypeAndName & arguments, const DataTypePtr & result_type) const override
    {
        /// isNullable(column) triggers a bug in old analyzer when it is replaced to constant.
        if (!use_analyzer)
            return nullptr;

        const ColumnWithTypeAndName & elem = arguments[0];
        if (elem.type->onlyNull() || canContainNull(*elem.type))
            return result_type->createColumnConst(1, UInt8(1));

        return result_type->createColumnConst(1, UInt8(0));
    }

    bool useDefaultImplementationForNulls() const override { return false; }

    bool useDefaultImplementationForNothing() const override { return false; }

    bool useDefaultImplementationForConstants() const override { return true; }

    bool useDefaultImplementationForLowCardinalityColumns() const override { return false; }

    ColumnNumbers getArgumentsThatDontImplyNullableReturnType(size_t /*number_of_arguments*/) const override { return {0}; }

    bool isSuitableForShortCircuitArgumentsExecution(const DataTypesWithConstInfo & /*arguments*/) const override { return false; }

    size_t getNumberOfArguments() const override
    {
        return 1;
    }

    DataTypePtr getReturnTypeImpl(const DataTypes & /*arguments*/) const override
    {
        return std::make_shared<DataTypeUInt8>();
    }

    ColumnPtr executeImpl(const ColumnsWithTypeAndName & arguments, const DataTypePtr &, size_t input_rows_count) const override
    {
        const auto & elem = arguments[0];
        return ColumnUInt8::create(input_rows_count, isColumnNullable(*elem.column) || elem.type->isLowCardinalityNullable());
    }

private:
    bool use_analyzer;
};

}

REGISTER_FUNCTION(IsNullable)
{
    factory.registerFunction<FunctionIsNullable>();
}

}