isPhoneVietNamValid function
Implementation
bool isPhoneVietNamValid(String value) {
late RegExp rex;
if (value.length > 2 && value.substring(0, 2) == '84') {
rex = RegExp(r'(84|0[3|5|7|8|9])+([0-9]{9})\b');
} else {
rex = RegExp(r'(84|0[3|5|7|8|9])+([0-9]{8})\b');
}
String? result = rex.firstMatch(value)?.input;
return result != null;
}