How to validate input with TMP_InputField according to mask?

Question

I am making a phone number form. The mask is +7(***)***-**-**. I am trying to make a custom TMP_Validator for this. The input still should look like +7(9**)***-**-**, +7(99*)***-**-** and so on.

What I have so far:

public override char Validate(ref string text, ref int pos, char ch)
    {
        if (ch == '\b')
        {
            return ch;
        }

        string numericText = new String(text.Where(c => char.IsDigit(c)).ToArray());

        if (numericText.Length < 11)
        {
            string proposedText = text.Substring(0, text.Length) + ch;

            if (Regex.IsMatch(proposedText, @"^\d{10}$"))
            {
                text = FormatPhoneNumber(proposedText);
                pos++;
                return ch;
            }
        }

        return '\0';
    }

But that does not work. Brain is melting, so I am here for your help.