isValidNationalNumber function
Checks if the given value is a valid National Number.
Implementation
bool isValidNationalNumber(String value) {
value = value.replaceAll('-', '').replaceAll(' ', '');
if (value.length != 10) return false;
var sum = 0;
for (var i = 0; i < value.length - 1; i++) {
var c = value.codeUnitAt(i) - 48;
if (c < 0 || c > 9) {
return false;
}
sum += (c) * (10 - i);
}
var d = value.codeUnitAt(9) - 48;
if (d < 0 || d > 9) return false;
var mod = sum % 11;
if (mod >= 2) mod = 11 - mod;
return mod == d;
}