public boolean isValidSelection(DateModel<?> model) {
        if (model.isSelected()) {
            Calendar value = Calendar.getInstance();
            value.set(model.getYear(), model.getMonth(), model.getDay());
            value.set(Calendar.HOUR, 0);
            value.set(Calendar.MINUTE, 0);
            value.set(Calendar.SECOND, 0);
            value.set(Calendar.MILLISECOND, 0);

            switch (value.get(Calendar.DAY_OF_WEEK)) {
                case Calendar.SATURDAY:
                case Calendar.SUNDAY:
                    return true;
                default:
                    return false;
            }
        } else {
            return true;
        }
    }