func FormatOutOfCountryCallingNumber()

in phonenumbers.go [1400:1463]
45 lines of code
9 McCabe index (conditional complexity)

func FormatOutOfCountryCallingNumber(
	number *PhoneNumber,
	regionCallingFrom string) string {

	if !isValidRegionCode(regionCallingFrom) {
		return Format(number, INTERNATIONAL)
	}
	countryCallingCode := int(number.GetCountryCode())
	nationalSignificantNumber := GetNationalSignificantNumber(number)
	if !hasValidCountryCallingCode(countryCallingCode) {
		return nationalSignificantNumber
	}
	if countryCallingCode == NANPA_COUNTRY_CODE {
		if IsNANPACountry(regionCallingFrom) {
			// For NANPA regions, return the national format for these
			// regions but prefix it with the country calling code.
			return strconv.Itoa(countryCallingCode) + " " + Format(number, NATIONAL)
		}
	} else if countryCallingCode == getCountryCodeForValidRegion(regionCallingFrom) {
		// If regions share a country calling code, the country calling
		// code need not be dialled. This also applies when dialling
		// within a region, so this if clause covers both these cases.
		// Technically this is the case for dialling from La Reunion to
		// other overseas departments of France (French Guiana, Martinique,
		// Guadeloupe), but not vice versa - so we don't cover this edge
		// case for now and for those cases return the version including
		// country calling code.
		// Details here: http://www.petitfute.com/voyage/225-info-pratiques-reunion
		return Format(number, NATIONAL)
	}
	// Metadata cannot be null because we checked 'isValidRegionCode()' above.
	metadataForRegionCallingFrom := getMetadataForRegion(regionCallingFrom)
	internationalPrefix := metadataForRegionCallingFrom.GetInternationalPrefix()

	// For regions that have multiple international prefixes, the
	// international format of the number is returned, unless there is
	// a preferred international prefix.
	internationalPrefixForFormatting := ""
	metPref := metadataForRegionCallingFrom.GetPreferredInternationalPrefix()
	if UNIQUE_INTERNATIONAL_PREFIX.MatchString(internationalPrefix) {
		internationalPrefixForFormatting = internationalPrefix
	} else if metPref != "" {
		internationalPrefixForFormatting = metPref
	}

	regionCode := GetRegionCodeForCountryCode(countryCallingCode)
	// Metadata cannot be null because the country calling code is valid.
	metadataForRegion :=
		getMetadataForRegionOrCallingCode(countryCallingCode, regionCode)
	formattedNationalNumber :=
		formatNsn(
			nationalSignificantNumber, metadataForRegion, INTERNATIONAL)
	formattedNumber := NewBuilder([]byte(formattedNationalNumber))
	maybeAppendFormattedExtension(number, metadataForRegion, INTERNATIONAL,
		formattedNumber)
	if len(internationalPrefixForFormatting) > 0 {
		formattedNumber.InsertString(0, internationalPrefixForFormatting+" "+
			strconv.Itoa(countryCallingCode)+" ")
	} else {
		prefixNumberWithCountryCallingCode(
			countryCallingCode, INTERNATIONAL, formattedNumber)
	}
	return formattedNumber.String()
}