ClickHouse/src/Functions/h3ToString.cpp

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

#include <h3api.h>

#define H3_INDEX_STRING_LENGTH 17 // includes \0 terminator

namespace DB
{
namespace ErrorCodes
{
    extern const int ILLEGAL_TYPE_OF_ARGUMENT;
}
class FunctionH3ToString : public IFunction
{
public:
    static constexpr auto name = "h3ToString";

    static FunctionPtr create(const Context &) { return std::make_shared<FunctionH3ToString>(); }

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

    size_t getNumberOfArguments() const override { return 1; }

    bool useDefaultImplementationForConstants() const override { return true; }

    DataTypePtr getReturnTypeImpl(const DataTypes & arguments) const override
    {
        const auto * arg = arguments[0].get();
        if (!WhichDataType(arg).isUInt64())
            throw Exception(
                "Illegal type " + arg->getName() + " of argument " + std::to_string(1) + " of function " + getName() + ". Must be UInt64",
                ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);

        return std::make_shared<DataTypeString>();
    }

    void executeImpl(Block & block, const ColumnNumbers & arguments, size_t result, size_t input_rows_count) const override
    {
        const auto * col_hindex = block.getByPosition(arguments[0]).column.get();

        auto col_res = ColumnString::create();
        auto & vec_res = col_res->getChars();
        auto & vec_offsets = col_res->getOffsets();

        vec_offsets.resize(input_rows_count);
        vec_res.resize_fill(input_rows_count * H3_INDEX_STRING_LENGTH, '\0');

        char * begin = reinterpret_cast<char *>(vec_res.data());
        char * pos = begin;

        for (size_t i = 0; i < input_rows_count; ++i)
        {
            const UInt64 hindex = col_hindex->getUInt(i);

            if (!h3IsValid(hindex))
            {
                throw Exception("Invalid H3 index: " + std::to_string(hindex), ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
            }
            h3ToString(hindex, pos, H3_INDEX_STRING_LENGTH);

            // move to end of the index
            while (*pos != '\0')
            {
                pos++;
            }
            vec_offsets[i] = ++pos - begin;
        }
        vec_res.resize(pos - begin);
        block.getByPosition(result).column = std::move(col_res);
    }
};


void registerFunctionH3ToString(FunctionFactory & factory)
{
    factory.registerFunction<FunctionH3ToString>();
}

}