getNationalPrefixTransformRule() public method

 /**
  * Strips any national prefix (such as 0, 1) present in the number provided.
  *
  * @param string $number  the normalized telephone number that we wish to strip any national
  *     dialing prefix from
  * @param PhoneMetadata $metadata  the metadata for the region that we think this number is from
  * @param string $carrierCode  a place to insert the carrier code if one is extracted
  * @return bool true if a national prefix or carrier code (or both) could be extracted.
  */
 public function maybeStripNationalPrefixAndCarrierCode(&$number, PhoneMetadata $metadata, &$carrierCode)
 {
     $numberLength = mb_strlen($number);
     $possibleNationalPrefix = $metadata->getNationalPrefixForParsing();
     if ($numberLength == 0 || $possibleNationalPrefix === null || mb_strlen($possibleNationalPrefix) == 0) {
         // Early return for numbers of zero length.
         return false;
     }
     // Attempt to parse the first digits as a national prefix.
     $prefixMatcher = new Matcher($possibleNationalPrefix, $number);
     if ($prefixMatcher->lookingAt()) {
         $nationalNumberRule = $metadata->getGeneralDesc()->getNationalNumberPattern();
         // Check if the original number is viable.
         $nationalNumberRuleMatcher = new Matcher($nationalNumberRule, $number);
         $isViableOriginalNumber = $nationalNumberRuleMatcher->matches();
         // $prefixMatcher->group($numOfGroups) === null implies nothing was captured by the capturing
         // groups in $possibleNationalPrefix; therefore, no transformation is necessary, and we just
         // remove the national prefix
         $numOfGroups = $prefixMatcher->groupCount();
         $transformRule = $metadata->getNationalPrefixTransformRule();
         if ($transformRule === null || mb_strlen($transformRule) == 0 || $prefixMatcher->group($numOfGroups - 1) === null) {
             // If the original number was viable, and the resultant number is not, we return.
             $matcher = new Matcher($nationalNumberRule, substr($number, $prefixMatcher->end()));
             if ($isViableOriginalNumber && !$matcher->matches()) {
                 return false;
             }
             if ($carrierCode !== null && $numOfGroups > 0 && $prefixMatcher->group($numOfGroups) !== null) {
                 $carrierCode .= $prefixMatcher->group(1);
             }
             $number = substr($number, $prefixMatcher->end());
             return true;
         } else {
             // Check that the resultant number is still viable. If not, return. Check this by copying
             // the string and making the transformation on the copy first.
             $transformedNumber = $number;
             $transformedNumber = substr_replace($transformedNumber, $prefixMatcher->replaceFirst($transformRule), 0, $numberLength);
             $matcher = new Matcher($nationalNumberRule, $transformedNumber);
             if ($isViableOriginalNumber && !$matcher->matches()) {
                 return false;
             }
             if ($carrierCode !== null && $numOfGroups > 1) {
                 $carrierCode .= $prefixMatcher->group(1);
             }
             $number = substr_replace($number, $transformedNumber, 0, mb_strlen($number));
             return true;
         }
     }
     return false;
 }