Escribir en un EditText tipo tarjeta de crédito

class CreditCardNumberFormatter implements TextWatcher {
    private boolean mFormatting;
    private boolean mDeletingHyphen;
    private int mHyphenStart;
    private boolean mDeletingBackward;

    CreditCardNumberFormatter() {}

    @Override
    public void onTextChanged(CharSequence s, int start, int before, int count) {
        if (!mFormatting) {
            mFormatting = true;
            int selStart = Selection.getSelectionStart(s);
            int selEnd = Selection.getSelectionEnd(s);

            StringBuilder formatted = new StringBuilder();
            for (int i = 0; i < s.length(); i++) {
                if (canInsertHyphen(i, s)) {
                    formatted.append('-');
                } else {
                    if (formatted.length() == 4 || formatted.length() == 9 || formatted.length() == 14) {
                        formatted.append(' ');
                    }
                    formatted.append(s.charAt(i));
                }
            }