// Source - https://stackoverflow.com/a/18760472
// Posted by torap, modified by community. See post 'Timeline' for change history
// Retrieved 2025-11-14, License - CC BY-SA 3.0

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string { if (textField.tag == 8) {           
        NSCharacterSet *numSet = [NSCharacterSet characterSetWithCharactersInString:@"0123456789-"];
        NSString *newString = [textField.text stringByReplacingCharactersInRange:range withString:string];
        int charCount = [newString length];

        if (charCount == 3 || charCount == 7) {
            if ([string isEqualToString:@""]){
                return YES;
            }else{
                newString = [newString stringByAppendingString:@"-"];
            }
        }

        if (charCount == 4 || charCount == 8) {
            if (![string isEqualToString:@"-"]){
                newString = [newString substringToIndex:[newString length]-1];
                newString = [newString stringByAppendingString:@"-"];
            }
        }

        if ([newString rangeOfCharacterFromSet:[numSet invertedSet]].location != NSNotFound
            || [string rangeOfString:@"-"].location != NSNotFound
            || charCount > 12) {
            return NO;
        }

        textField.text = newString;
    return NO;
}    
return YES;}