text: #if !defined(ARCADIA_BUILD)
  #    include "config_functions.h"
  #endif
  
  #if USE_H3
  
  #include <Columns/ColumnsNumber.h>
  #include <DataTypes/DataTypesNumber.h>
  #include <Functions/FunctionFactory.h>
  #include <Functions/IFunction.h>
  #include <IO/WriteHelpers.h>
  #include <Common/typeid_cast.h>
  #include <ext/range.h>
  
  #include <constants.h>
  #include <h3api.h>
  
  
  namespace DB
  {
  namespace ErrorCodes
  {
      extern const int ILLEGAL_TYPE_OF_ARGUMENT;
      extern const int ARGUMENT_OUT_OF_BOUND;
  }
  
  namespace
  {
  
  // Average metric edge length of H3 hexagon. The edge length `e` for given resolution `res` can
  // be used for converting metric search radius `radius` to hexagon search ring size `k` that is
  // used by `H3kRing` function. For small enough search area simple flat approximation can be used,
  // i.e. the smallest `k` that satisfies relation `3 k^2 - 3 k + 1 >= (radius / e)^2` should be
  // chosen
  class FunctionH3EdgeLengthM : public IFunction
  {
  public:
      static constexpr auto name = "h3EdgeLengthM";
  
      static FunctionPtr create(const Context &) { return std::make_shared<FunctionH3EdgeLengthM>(); }
  
      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).isUInt8())
              throw Exception(
                  "Illegal type " + arg->getName() + " of argument " + std::to_string(1) + " of function " + getName() + ". Must be UInt8",
                  ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
  
          return std::make_shared<DataTypeFloat64>();
      }
  
      ColumnPtr executeImpl(ColumnsWithTypeAndName & arguments, const DataTypePtr &, size_t input_rows_count) const override
      {
          const auto * col_hindex = arguments[0].column.get();
  
          auto dst = ColumnVector<Float64>::create();
          auto & dst_data = dst->getData();
          dst_data.resize(input_rows_count);
  
          for (const auto row : ext::range(0, input_rows_count))
          {
              const UInt64 resolution = col_hindex->getUInt(row);
              if (resolution > MAX_H3_RES)
                  throw Exception("The argument 'resolution' (" + toString(resolution) + ") of function " + getName()
                      + " is out of bounds because the maximum resolution in H3 library is " + toString(MAX_H3_RES), ErrorCodes::ARGUMENT_OUT_OF_BOUND);
  
              Float64 res = edgeLengthM(resolution);
  
              dst_data[row] = res;
          }
  
          return dst;
      }
  };
  
  }
  
  void registerFunctionH3EdgeLengthM(FunctionFactory & factory)
  {
      factory.registerFunction<FunctionH3EdgeLengthM>();
  }
  
  }
  
  #endif
  