private function isValid(Constraint $constraint, int $difference): bool
    {
        /*
         * It's a earlier than today date?
         * Nothing to do
         */
        if ($constraint instanceof EarlierThanToday && $difference < 0) {
            return true;
        }

        /*
         * It's a earlier than or equal today date?
         * Nothing to do
         */
        if ($constraint instanceof EarlierThanOrEqualToday && $difference <= 0) {
            return true;
        }

        /*
         * It's a later than today date?
         * Nothing to do
         */
        if ($constraint instanceof LaterThanToday && $difference > 0) {
            return true;
        }

        /*
         * It's a later than or equal today date?
         * Nothing to do
         */
        if ($constraint instanceof LaterThanOrEqualToday && $difference >= 0) {
            return true;
        }

        return false;
    }