Status GenerateLevels()

in src/parquet/arrow/writer.cc [110:180]
60 lines of code
9 McCabe index (conditional complexity)

  Status GenerateLevels(const Array& array, const std::shared_ptr<Field>& field,
                        int64_t* values_offset, int64_t* num_values, int64_t* num_levels,
                        const std::shared_ptr<ResizableBuffer>& def_levels_scratch,
                        std::shared_ptr<Buffer>* def_levels_out,
                        std::shared_ptr<Buffer>* rep_levels_out,
                        std::shared_ptr<Array>* values_array) {
    // Work downwards to extract bitmaps and offsets
    min_offset_idx_ = 0;
    max_offset_idx_ = array.length();
    RETURN_NOT_OK(VisitInline(array));
    *num_values = max_offset_idx_ - min_offset_idx_;
    *values_offset = min_offset_idx_;
    *values_array = values_array_;

    // Walk downwards to extract nullability
    std::shared_ptr<Field> current_field = field;
    nullable_.push_back(current_field->nullable());
    while (current_field->type()->num_children() > 0) {
      if (current_field->type()->num_children() > 1) {
        return Status::NotImplemented(
            "Fields with more than one child are not supported.");
      } else {
        current_field = current_field->type()->child(0);
      }
      nullable_.push_back(current_field->nullable());
    }

    // Generate the levels.
    if (nullable_.size() == 1) {
      // We have a PrimitiveArray
      *rep_levels_out = nullptr;
      if (nullable_[0]) {
        RETURN_NOT_OK(
            def_levels_scratch->Resize(array.length() * sizeof(int16_t), false));
        auto def_levels_ptr =
            reinterpret_cast<int16_t*>(def_levels_scratch->mutable_data());
        if (array.null_count() == 0) {
          std::fill(def_levels_ptr, def_levels_ptr + array.length(), 1);
        } else if (array.null_count() == array.length()) {
          std::fill(def_levels_ptr, def_levels_ptr + array.length(), 0);
        } else {
          ::arrow::internal::BitmapReader valid_bits_reader(
              array.null_bitmap_data(), array.offset(), array.length());
          for (int i = 0; i < array.length(); i++) {
            def_levels_ptr[i] = valid_bits_reader.IsSet() ? 1 : 0;
            valid_bits_reader.Next();
          }
        }

        *def_levels_out = def_levels_scratch;
      } else {
        *def_levels_out = nullptr;
      }
      *num_levels = array.length();
    } else {
      RETURN_NOT_OK(rep_levels_.Append(0));
      RETURN_NOT_OK(HandleListEntries(0, 0, 0, array.length()));

      std::shared_ptr<Array> def_levels_array;
      std::shared_ptr<Array> rep_levels_array;

      RETURN_NOT_OK(def_levels_.Finish(&def_levels_array));
      RETURN_NOT_OK(rep_levels_.Finish(&rep_levels_array));

      *def_levels_out = static_cast<PrimitiveArray*>(def_levels_array.get())->values();
      *rep_levels_out = static_cast<PrimitiveArray*>(rep_levels_array.get())->values();
      *num_levels = rep_levels_array->length();
    }

    return Status::OK();
  }