This Month or Later Only, Please! (TEC 2.0.10)

// Don't allow anything earlier than this month to be displayed in the gridview
if (isset($eventDate) and isset($eventDisplay) and $eventDisplay === 'month') {
    $thisMonth = date('Y-m').'-01';
    $redirectTo = get_site_url();

    // Is the user requesting something earlier than this month?
    if ($eventDate < $thisMonth) {
        // Redirect if possible
        if (!headers_sent()) {
            header("Location: $redirectTo");
            exit();
        }
        // If not possible to redirect, show an error message or 404
        else {
            get_template_part('404');
        }
    }
}