// see https://howtodoinjava.com/java/regex/java-regex-validate-international-phone-numbers/
sclass InternationalPhoneValidator {
  S rawInput;
  S filtered;
  L<CountryDialCode> dialCodes; // might be multiple countries with same code
  S countryPart, localPart;
  bool valid;
  S error;
  
  *() {}
  *(S *rawInput) {}
  
  // needs rawInput
  run {
    filtered = dropPrefix("+", dropSpecialChars(rawInput));
    if (!isAllDigits(filtered)) ret with error = "Bad characters";
    splitLocal();
  }
  
  S dropSpecialChars(S s) {
    ret replaceAll(s, "[\\s\\(\\)\\-]", "");
  }
  
  void splitLocal {
    S countryPart = longestPrefixInNavigableSet(filtered, navigableKeys(countryDialCodes_rawNumbersTreeMultiMap()));
    if (countryPart == null) ret with error = "Invalid country code";
    dialCodes = countryDialCodes_rawNumbersTreeMultiMap().get(countryPart);
    localPart = dropPrefix(countryPart, filtered);
    if (l(filtered) < 7) ret with error = "Phone number too short";
    else if (l(filtered) > 15) ret with error = "Phone number too long";
    valid = true;
  }
}

Began life as a copy of #1023353