ClickHouse/src/Functions/stem.cpp

#include <Columns/ColumnString.h>
#include <DataTypes/DataTypeString.h>
#include <Functions/FunctionFactory.h>
#include <Functions/FunctionHelpers.h>
#include <Functions/IFunction.h>

#include <libstemmer.h>


namespace DB
{
namespace ErrorCodes
{
    extern const int ILLEGAL_COLUMN;
    extern const int ILLEGAL_TYPE_OF_ARGUMENT;
}

namespace
{

struct StemImpl
{
    static void vector(
        const ColumnString::Chars & data,
        const ColumnString::Offsets & offsets,
        ColumnString::Chars & res_data,
        ColumnString::Offsets & res_offsets,
        const String & language)
    {
        struct sb_stemmer * stemmer = sb_stemmer_new(language.data(), "UTF_8");
        
        if (stemmer == nullptr)
        {
            throw Exception(
            "Language " + language + " is not supported for function stem",
            ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
        }

        res_data.resize(data.size());
        res_offsets.assign(offsets);

        UInt64 data_size = 0;
        for (UInt64 i = 0; i < offsets.size(); ++i)
        {
            /// Note that accessing -1th element is valid for PaddedPODArray.
            size_t original_size = offsets[i] - offsets[i - 1];
            const sb_symbol * result = sb_stemmer_stem(stemmer, reinterpret_cast<const unsigned char *>(data.data() + offsets[i - 1]), original_size - 1);
            size_t new_size = sb_stemmer_length(stemmer) + 1;

            memcpy(res_data.data() + data_size, result, new_size);
            
            data_size += new_size;
            res_offsets[i] = data_size;
        }
        res_data.resize(data_size);
        sb_stemmer_delete(stemmer);
    }
};


class FunctionStem : public IFunction
{
public:
    static constexpr auto name = "stem";
    static FunctionPtr create(ContextPtr) { return std::make_shared<FunctionStem>(); }

    String getName() const override { return name; }

    size_t getNumberOfArguments() const override { return 2; }

    DataTypePtr getReturnTypeImpl(const DataTypes & arguments) const override
    {
        if (!isString(arguments[0]))
            throw Exception(
                "Illegal type " + arguments[0]->getName() + " of argument of function " + getName(), ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
        if (!isString(arguments[1]))
            throw Exception(
                "Illegal type " + arguments[1]->getName() + " of argument of function " + getName(), ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
        return arguments[1];
    }

    bool useDefaultImplementationForConstants() const override { return true; }

    ColumnNumbers getArgumentsThatAreAlwaysConstant() const override { return {0}; }

    ColumnPtr executeImpl(const ColumnsWithTypeAndName & arguments, const DataTypePtr &, size_t) const override
    {
        const auto & langcolumn = arguments[0].column;
        const auto & strcolumn = arguments[1].column;

        const ColumnConst * lang_col = checkAndGetColumn<ColumnConst>(langcolumn.get());
        const ColumnString * words_col = checkAndGetColumn<ColumnString>(strcolumn.get());

        if (!lang_col) 
            throw Exception(
                "Illegal column " + arguments[0].column->getName() + " of argument of function " + getName(), ErrorCodes::ILLEGAL_COLUMN);
        if (!words_col)
            throw Exception(
                "Illegal column " + arguments[1].column->getName() + " of argument of function " + getName(), ErrorCodes::ILLEGAL_COLUMN);

        String language = lang_col->getValue<String>();

        auto col_res = ColumnString::create();
        StemImpl::vector(words_col->getChars(), words_col->getOffsets(), col_res->getChars(), col_res->getOffsets(), language);
        return col_res;
    }
};

}

void registerFunctionStem(FunctionFactory & factory)
{
    factory.registerFunction<FunctionStem>(FunctionFactory::CaseInsensitive);
}

}