Escribir en un EditText tipo tarjeta de crédito

@Override
    public void beforeTextChanged(CharSequence s, int start, int count, int after) {
    }

    @Override
    public void onTextChanged(CharSequence s, int start, int before, int count) {
        //s.charAt(0) == '-' && s.length() == 1
        if (s.toString().length() != 0) {
            if (s.toString().charAt(0) == '-') {
                if (s.length() != 1) {
                    String aux = s.toString().substring(1);
                    if (aux.length() <= 16) {
                        int aux2 = aux.length();
                        aux2 = aux2 - aux2 % 4;
                        StringBuilder sb = new StringBuilder();
                        for (int i = 0; i < aux.length(); i++) {
                            if (i % 4 == 0 && i != 0) {
                                sb.append("-");
                            }
                            sb.append(aux.charAt(i));
                        }