#include <Functions/IFunction.h>
#include <Functions/FunctionFactory.h>
#include <DataTypes/DataTypeNullable.h>
#include <Columns/ColumnNullable.h>
#include <Core/ColumnNumbers.h>


namespace DB
{
namespace
{

/// If value is not Nullable or NULL, wraps it to Nullable.
class FunctionToNullable : public IFunction
{
public:
    static constexpr auto name = "toNullable";

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

    std::string getName() const override
    {
        return name;
    }

    size_t getNumberOfArguments() const override { return 1; }
    bool useDefaultImplementationForNulls() const override { return false; }
    bool useDefaultImplementationForConstants() const override { return true; }
    bool isSuitableForShortCircuitArgumentsExecution() const override { return false; }

    DataTypePtr getReturnTypeImpl(const DataTypes & arguments) const override
    {
        return makeNullable(arguments[0]);
    }

    ColumnPtr executeImpl(const ColumnsWithTypeAndName & arguments, const DataTypePtr &, size_t) const override
    {
        return makeNullable(arguments[0].column);
    }
};

}

void registerFunctionToNullable(FunctionFactory & factory)
{
    factory.registerFunction<FunctionToNullable>();
}

}