std::string ProperCaseHeaderKeyFormatter::format(absl::string_view key) const {

  auto copy = std::string(key);

  bool should_capitalize = true;

  for (char& c : copy) {

    if (should_capitalize && isalpha(c)) {

      c = static_cast<char>(toupper(c));

    }

    should_capitalize = !isalpha(c) && !isdigit(c);

  }

  return copy;

}