func maybeStripNationalPrefixAndCarrierCode()

in phonenumbers.go [2680:2741]
48 lines of code
16 McCabe index (conditional complexity)

func maybeStripNationalPrefixAndCarrierCode(
	number *Builder,
	metadata *PhoneMetadata,
	carrierCode *Builder) bool {

	numberLength := len(number.String())
	possibleNationalPrefix := metadata.GetNationalPrefixForParsing()
	if numberLength == 0 || len(possibleNationalPrefix) == 0 {
		// Early return for numbers of zero length.
		return false
	}
	possibleNationalPrefix = "^(?:" + possibleNationalPrefix + ")" // Strictly match from string start
	// Attempt to parse the first digits as a national prefix.
	prefixMatcher := regexFor(possibleNationalPrefix)
	if prefixMatcher.MatchString(number.String()) {
		natRulePattern := "^(?:" + metadata.GetGeneralDesc().GetNationalNumberPattern() + ")$" // Strictly match
		nationalNumberRule := regexFor(natRulePattern)
		// Check if the original number is viable.
		isViableOriginalNumber := nationalNumberRule.Match(number.Bytes())
		// prefixMatcher.group(numOfGroups) == null implies nothing was
		// captured by the capturing groups in possibleNationalPrefix;
		// therefore, no transformation is necessary, and we just
		// remove the national prefix.
		groups := prefixMatcher.FindSubmatchIndex(number.Bytes())
		numOfGroups := len(groups)/2 - 1 // groups is a list of index pairs, idx0,idx1 defines the whole match, idx2+ submatches.
		// Subtract one to ignore group(0) in count
		transformRule := metadata.GetNationalPrefixTransformRule()
		if len(transformRule) == 0 || groups[numOfGroups*2] < 0 { // Negative idx means subgroup did not match
			// If the original number was viable, and the resultant number
			// is not, we return.
			if isViableOriginalNumber &&
				!nationalNumberRule.MatchString(
					number.String()[groups[1]:]) { // groups[1] == last match idx
				return false
			}
			if len(carrierCode.Bytes()) != 0 &&
				numOfGroups > 0 &&
				groups[numOfGroups*2] > 0 { // Negative idx means subgroup did not match
				carrierCode.Write(number.Bytes()[groups[numOfGroups*2]:groups[numOfGroups*2+1]])
			}
			number.ResetWith(number.Bytes()[groups[1]:])
			return true
		} else {
			// Check that the resultant number is still viable. If not,
			// return. Check this by copying the string buffer and
			// making the transformation on the copy first.
			numString := number.String()
			transformedNumBytes := []byte(prefixMatcher.ReplaceAllString(numString, transformRule))
			if isViableOriginalNumber &&
				!nationalNumberRule.Match(transformedNumBytes) {
				return false
			}
			if len(carrierCode.Bytes()) != 0 && numOfGroups > 1 && groups[2] != -1 { // Check group(1) got a submatch
				carrC := numString[groups[2]:groups[3]] // group(1) idxs
				carrierCode.WriteString(carrC)
			}
			number.ResetWith(transformedNumBytes)
			return true
		}
	}
	return false
}