gatherpress-rsvp-action.php

<?php
/*
Plugin Name: GatherPress RSVP Action
Description: Sends an email, whenever someone sends an RSVP
Version: 0.0.1
Author: Carsten Bach
*/

/**
 * Fires immediately after a comment is inserted into the database.
 *
 * @see https://developer.wordpress.org/reference/hooks/wp_insert_comment/
 *
 * @param int         $id      The comment ID.
 * @param \WP_Comment $comment Comment object.
 */
function gatherpress_rsvp_on_wp_insert_comment_787( int $id, \WP_Comment $comment ): void {
    if ( 'gatherpress_rsvp' !== $comment->comment_type ) {
        return;
    }

    $mail     = get_option( 'admin_email' );
    $attendee = get_userdata( $comment->user_id );
    $subject  = sprintf(
        'New RSVP by: %s',
        $attendee->display_name
    );
    $event_title = get_the_title( $comment->comment_post_ID );
    $message     = sprintf(
        '%s sent an RSVP for %s.',
        $attendee->display_name,
        $event_title
    );

    wp_mail( $mail, $subject, $message );
}
add_action( 'wp_insert_comment', 'gatherpress_rsvp_on_wp_insert_comment_787', 10, 2 );