public function formatNsnUsingPattern(
        $nationalNumber,
        NumberFormat $formattingPattern,
        $numberFormat,
        $carrierCode = null
    ) {
        $numberFormatRule = $formattingPattern->getFormat();
        $m = new Matcher($formattingPattern->getPattern(), $nationalNumber);
        if ($numberFormat === PhoneNumberFormat::NATIONAL &&
            $carrierCode !== null && mb_strlen($carrierCode) > 0 &&
            mb_strlen($formattingPattern->getDomesticCarrierCodeFormattingRule()) > 0
        ) {
            // Replace the $CC in the formatting rule with the desired carrier code.
            $carrierCodeFormattingRule = $formattingPattern->getDomesticCarrierCodeFormattingRule();
            $carrierCodeFormattingRule = str_replace(static::CC_STRING, $carrierCode, $carrierCodeFormattingRule);
            // Now replace the $FG in the formatting rule with the first group and the carrier code
            // combined in the appropriate way.
            $firstGroupMatcher = new Matcher(static::FIRST_GROUP_PATTERN, $numberFormatRule);
            $numberFormatRule = $firstGroupMatcher->replaceFirst($carrierCodeFormattingRule);
            $formattedNationalNumber = $m->replaceAll($numberFormatRule);
        } else {
            // Use the national prefix formatting rule instead.
            $nationalPrefixFormattingRule = $formattingPattern->getNationalPrefixFormattingRule();
            if ($numberFormat == PhoneNumberFormat::NATIONAL &&
                $nationalPrefixFormattingRule !== null &&
                mb_strlen($nationalPrefixFormattingRule) > 0
            ) {
                $firstGroupMatcher = new Matcher(static::FIRST_GROUP_PATTERN, $numberFormatRule);
                $formattedNationalNumber = $m->replaceAll(
                    $firstGroupMatcher->replaceFirst($nationalPrefixFormattingRule)
                );
            } else {
                $formattedNationalNumber = $m->replaceAll($numberFormatRule);
            }
        }
        if ($numberFormat == PhoneNumberFormat::RFC3966) {
            // Strip any leading punctuation.
            $matcher = new Matcher(static::$SEPARATOR_PATTERN, $formattedNationalNumber);
            if ($matcher->lookingAt()) {
                $formattedNationalNumber = $matcher->replaceFirst('');
            }
            // Replace the rest with a dash between each number group.
            $formattedNationalNumber = $matcher->reset($formattedNationalNumber)->replaceAll('-');
        }
        return $formattedNationalNumber;
    }