How to limit the amount of entered decimal characters in textField?

I have a textField where user can enter a number which can has a decimals. I want to restrict the amount of decimal characters possible to enter till 4.

I'm trying to reach this behaviour with this code:

let split = completeString.components(separatedBy: ".")
    if split.count == 2 {
        print(split.last!)
        if split.last!.count >= 4 {
            return false
        }
    }

Full code for shouldChangeCharactersIn method:

 func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    let formatter = converterManager.setupNumberFormatter()
    
    let textString = textField.text ?? ""
    guard let range = Range(range, in: textString) else { return false }
    let updatedString = textString.replacingCharacters(in: range, with: string)
    let correctDecimalString = updatedString.replacingOccurrences(of: ",", with: ".")
    let completeString = correctDecimalString.replacingOccurrences(of: formatter.groupingSeparator, with: "")
    
    let split = completeString.components(separatedBy: ".")
    if split.count == 2 {
        print(split.last!)
        if split.last!.count >= 4 {
            return false
        }
    }
    
    numberFromTextField = completeString.isEmpty ? 0 : Double(completeString)
    guard completeString.count <= 12 else { return false }
    guard !completeString.isEmpty else { return true }
    
    textField.text = formatter.string(for: numberFromTextField)
    return string == formatter.decimalSeparator
}
}

This code successfully split the string, give me the numbers user enters after decimal sign, but:

• textField shows 3 character instead of 4
• print shows that despite textField shows 3, when I press 4th digits in shows in the split array
• when after 4th digit I continue to press numbers it changes last digit. I want if there is a 4 numbers entered already allow only delete not change the last number

GIF with behaviour: https://cln.sh/5vf1iq

How to fix that behaviour?