public static bool ContainsOnlyValidXChars(
PhoneNumber number, String candidate, PhoneNumberUtil util)
{
// The characters 'x' and 'X' can be (1) a carrier code, in which case they always precede the
// national significant number or (2) an extension sign, in which case they always precede the
// extension number. We assume a carrier code is more than 1 digit, so the first case has to
// have more than 1 consecutive 'x' or 'X', whereas the second case can only have exactly 1 'x'
// or 'X'. We ignore the character if it appears as the last character of the string.
for (int index = 0; index < candidate.Length - 1; index++)
{
char charAtIndex = candidate[index];
if (charAtIndex == 'x' || charAtIndex == 'X')
{
char charAtNextIndex = candidate[index + 1];
if (charAtNextIndex == 'x' || charAtNextIndex == 'X')
{
// This is the carrier code case, in which the 'X's always precede the national
// significant number.
index++;
if (util.IsNumberMatch(number, candidate.Substring(index)) != PhoneNumberUtil.MatchType.NSN_MATCH)
{
return(false);
}
// This is the extension sign case, in which the 'x' or 'X' should always precede the
// extension number.
}
else if (!PhoneNumberUtil.NormalizeDigitsOnly(candidate.Substring(index)).Equals(
number.Extension))
{
return(false);
}
}
}
return(true);
}