ClickHouse/src/Functions/stem.cpp

#include <Functions/FunctionStringToString.h>
#include <Functions/FunctionFactory.h>
//#include <Poco/Unicode.h>


#include <Columns/ColumnString.h>
#include <Columns/ColumnVector.h>
#include <DataTypes/DataTypeString.h>
#include <DataTypes/DataTypesNumber.h>
#include <Functions/FunctionFactory.h>
#include <Functions/FunctionHelpers.h>
#include <Functions/IFunctionImpl.h>
#include <Functions/castTypeToEither.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,
        struct sb_stemmer * stemmer)
    {
        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
{
    template <typename F>
    static bool castType(const IDataType * type, F && f)
    {
        return castTypeToEither<DataTypeUInt8, DataTypeUInt16, DataTypeUInt32, DataTypeUInt64>(type, std::forward<F>(f));
    }

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;
        ColumnPtr res;

        if (const ColumnString * col = checkAndGetColumn<ColumnString>(strcolumn.get())) 
        {
            if (const ColumnConst * scale_column_num = checkAndGetColumn<ColumnConst>(langcolumn.get()))
            {
                String language = scale_column_num->getValue<String>();
                struct sb_stemmer * stemmer = sb_stemmer_new(language.data(), "UTF_8");

                if (stemmer != nullptr)
                {
                    auto col_res = ColumnString::create();
                    StemImpl::vector(col->getChars(), col->getOffsets(), col_res->getChars(), col_res->getOffsets(), stemmer);
                    return col_res;
                }
                else 
                {
                    throw Exception(
                    "Language " + language + " is not supported for function " + getName(),
                    ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
                }
            }
        }

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

}

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

}