An extension on strings to format inputted string to required international format. Currently static and not injectable.

util.dart

extension StringNumberExtension on String {
  static final zeroFirstDigitRegExp = RegExp('^0');
  static final internationalFormatWithPlusFirstDigitsRegExp =
      RegExp('^[+234]{4}');
  static final internationalFormatWithoutPlusFirstDigitsRegExp =
      RegExp('^[234]{3}');

  String toNumberFormat() {
    if (isEmpty) {
      return '';
    }

    if (contains(zeroFirstDigitRegExp)) {
      return replaceFirst(zeroFirstDigitRegExp, '+234');
    }

    if (contains(internationalFormatWithPlusFirstDigitsRegExp)) {
      return this;
    }

    if (contains(internationalFormatWithoutPlusFirstDigitsRegExp)) {
      return '+$this';
    }

    return '+234$this';
  }

  String toLocalNumberFormat() {
    if (isEmpty) {
      return '';
    }

    if (contains(internationalFormatWithPlusFirstDigitsRegExp)) {
      return replaceFirst(internationalFormatWithPlusFirstDigitsRegExp, '0');
    }

    if (contains(internationalFormatWithoutPlusFirstDigitsRegExp)) {
      return replaceFirst(internationalFormatWithoutPlusFirstDigitsRegExp, '0');
    }

    return this;
  }
}