func maybeExtractCountryCode()

in phonenumbers.go [2545:2623]
62 lines of code
13 McCabe index (conditional complexity)

func maybeExtractCountryCode(
	number string,
	defaultRegionMetadata *PhoneMetadata,
	nationalNumber *Builder,
	keepRawInput bool,
	phoneNumber *PhoneNumber) (int, error) {

	if len(number) == 0 {
		return 0, nil
	}
	fullNumber := NewBuilderString(number)
	// Set the default prefix to be something that will never match.
	possibleCountryIddPrefix := "NonMatch"
	if defaultRegionMetadata != nil {
		possibleCountryIddPrefix = defaultRegionMetadata.GetInternationalPrefix()
	}

	countryCodeSource :=
		maybeStripInternationalPrefixAndNormalize(fullNumber, possibleCountryIddPrefix)
	if keepRawInput {
		phoneNumber.CountryCodeSource = &countryCodeSource
	}
	if countryCodeSource != PhoneNumber_FROM_DEFAULT_COUNTRY {
		if len(fullNumber.String()) <= MIN_LENGTH_FOR_NSN {
			return 0, ErrTooShortAfterIDD
		}
		potentialCountryCode := extractCountryCode(fullNumber, nationalNumber)
		if potentialCountryCode != 0 {
			phoneNumber.CountryCode = proto.Int32(int32(potentialCountryCode))
			return potentialCountryCode, nil
		}

		// If this fails, they must be using a strange country calling code
		// that we don't recognize, or that doesn't exist.
		return 0, ErrInvalidCountryCode
	} else if defaultRegionMetadata != nil {
		// Check to see if the number starts with the country calling code
		// for the default region. If so, we remove the country calling
		// code, and do some checks on the validity of the number before
		// and after.
		defaultCountryCode := int(defaultRegionMetadata.GetCountryCode())
		defaultCountryCodeString := strconv.Itoa(defaultCountryCode)
		normalizedNumber := fullNumber.String()
		if strings.HasPrefix(normalizedNumber, defaultCountryCodeString) {
			var (
				potentialNationalNumber = NewBuilderString(
					normalizedNumber[len(defaultCountryCodeString):])
				generalDesc        = defaultRegionMetadata.GetGeneralDesc()
				patP               = `^(?:` + generalDesc.GetNationalNumberPattern() + `)$` // Strictly match
				validNumberPattern = regexFor(patP)
			)
			maybeStripNationalPrefixAndCarrierCode(
				potentialNationalNumber,
				defaultRegionMetadata,
				NewBuilder(nil) /* Don't need the carrier code */)

			// If the number was not valid before but is valid now, or
			// if it was too long before, we consider the number with
			// the country calling code stripped to be a better result and
			// keep that instead.
			fullValid := validNumberPattern.MatchString(fullNumber.String())
			nationalValid := validNumberPattern.MatchString(potentialNationalNumber.String())
			lengthValid := testNumberLength(fullNumber.String(), defaultRegionMetadata, UNKNOWN)

			if (!fullValid && nationalValid) || lengthValid == TOO_LONG {
				nationalNumber.Write(potentialNationalNumber.Bytes())
				if keepRawInput {
					val := PhoneNumber_FROM_NUMBER_WITHOUT_PLUS_SIGN
					phoneNumber.CountryCodeSource = &val
				}
				phoneNumber.CountryCode = proto.Int32(int32(defaultCountryCode))
				return defaultCountryCode, nil
			}
		}
	}
	// No country calling code present.
	phoneNumber.CountryCode = proto.Int32(0)
	return 0, nil
}