Notification query optimization

add_action( 'wcfm_page_heading', function() {
    global $WCFM, $wpdb;
    if(apply_filters( 'wcfm_is_allow_notifications', true )) {
        $message_to = apply_filters( 'wcfm_message_author', get_current_user_id() );
        if( !$message_to || !wcfm_is_allow_wcfm() ) return;
        $total_messages = 0;
        if( wcfm_is_vendor() || ( function_exists( 'wcfm_is_delivery_boy' ) && wcfm_is_delivery_boy() ) || ( function_exists( 'wcfm_is_affiliate' ) && wcfm_is_affiliate() ) ) {
            $cache_key = $WCFM->wcfm_notification->cache_group . '-message-' . $message_to;
        } else {
            $cache_key = $WCFM->wcfm_notification->cache_group . '-message-0';
        }
        $total_messages = get_transient( $cache_key );
        if( empty( $total_messages ) ) {
            $sql = 'SELECT COUNT(wcfm_messages.ID) FROM ' . $wpdb->prefix . 'wcfm_messages AS wcfm_messages';
            $sql .= ' WHERE 1=1';

            $status_filter = " AND `is_direct_message` = 1";
            $sql .= $status_filter;

            if( wcfm_is_vendor() || ( function_exists( 'wcfm_is_delivery_boy' ) && wcfm_is_delivery_boy() ) || ( function_exists( 'wcfm_is_affiliate' ) && wcfm_is_affiliate() ) ) {
                $vendor_filter = " AND ( `author_id` = {$message_to} OR `message_to` = -1 OR `message_to` = {$message_to} )";
                $sql .= $vendor_filter;
            } else {
                $group_manager_filter = apply_filters( 'wcfm_notification_group_manager_filter', '' );
                if( $group_manager_filter ) {
                    $sql .= $group_manager_filter;
                } else {
                    $sql .= " AND `author_id` != -1";
                }
            }
            $message_status_filter = " ID NOT IN (SELECT message FROM {$wpdb->prefix}wcfm_messages_modifier WHERE read_by={$message_to})";
            $sql .= $message_status_filter;

            $total_messages = $wpdb->get_var( $sql );

            set_transient( $cache_key, $total_messages );
        }
    }
}, 9 );