Replaces a registration form with a waitlist form when a custom attendee limit is reached. Counts attendees using a List field and displays seats remaining.

event-reg-limit-waitlist-form-switch.php

<?php
/**
 * Plugin Name: Event Registration Limiter for Gravity Forms
 * Description: Dynamically switches between a registration form and a waitlist form
 *              based on the actual number of attendees registered.
 * Author: Chris Eggleston – Gravity Ranger
 * Tutorial URL: https://gravityranger.com/automatically-switch-from-a-registration-form-to-a-waitlist-in-gravity-forms/
 *
 * WHERE TO PUT THIS CODE:
 * --------------------------------------------------
 * Choose ONE of the following:
 *
 * OPTION A: Create a small custom plugin
 *   - Create a file called event-registration-limiter.php
 *   - Place it in /wp-content/plugins/
 *   - Paste this entire snippet into the file
 *   - Activate the plugin in WordPress
 *
 * OPTION B: Use a code snippet plugin
 *   - Add this code using WPCode, Code Snippets, etc.
 *   - Ensure the snippet runs on the front end
 *
 * OPTION C: functions.php
 *   - Paste into your active theme’s functions.php file
 *   - Code will be lost if the theme is changed
 *
 * --------------------------------------------------
 *
 * HOW TO USE:
 * 1. Create a registration form in Gravity Forms.
 * 2. Add a LIST field where EACH ROW represents ONE attendee
 *    (ex: First Name | Last Name | Email).
 * 3. Create a separate waitlist form.
 * 4. Place the shortcode on a page and pass the correct IDs.
 *
 * Example shortcode: 
 * [event_form_display registration_form_id="1" waitlist_form_id="2" list_field_id="6" max_attendees="100"]
 */

add_shortcode('event_form_display', function($atts) {

    /**
     * STEP 1: Define shortcode attributes
     *
     * These allow the snippet to be reused for different events
     * without modifying the code.
     */
    $atts = shortcode_atts([
        'registration_form_id' => 1,   // Main event registration form ID
        'waitlist_form_id'     => 2,   // Waitlist form ID
        'list_field_id'        => 6,   // List field ID (each row = 1 attendee)
        'max_attendees'        => 100  // Event capacity
    ], $atts);

    // Cast values to integers for safety
    $registration_form_id = (int) $atts['registration_form_id'];
    $waitlist_form_id     = (int) $atts['waitlist_form_id'];
    $list_field_id        = (int) $atts['list_field_id'];
    $max_attendees        = (int) $atts['max_attendees'];

    /**
     * STEP 2: Retrieve all active entries for the registration form
     */
    $search_criteria = array('status' => 'active');
    $entries = GFAPI::get_entries($registration_form_id, $search_criteria);

    /**
     * STEP 3: Count total attendees
     *
     * Each row in the List field represents ONE attendee.
     * We loop through all entries and sum the row counts.
     */
    $total_attendees = 0;

    foreach ($entries as $entry) {
        $list_value = rgar($entry, $list_field_id);

        if (!empty($list_value)) {
            $list = maybe_unserialize($list_value);

            if (is_array($list)) {
                $total_attendees += count($list);
            }
        }
    }

    /**
     * STEP 4: Calculate remaining seats
     */
    $seats_remaining = $max_attendees - $total_attendees;

    /**
     * STEP 5: Display the correct form
     *
     * - If the event is full, show the waitlist form
     * - Otherwise, show the registration form with seats remaining
     */
    if ($seats_remaining <= 0) {

        $output  = '<div class="gf-event-message">';
        $output .= '⚠️ Registration is full. You can join the waitlist below:';
        $output .= '</div>';

        $output .= do_shortcode(
            '[gravityform id="' . $waitlist_form_id . '" title="false" description="false" ajax="true"]'
        );

    } else {

        $output  = '<div class="gf-event-message">';
        $output .= '🎟️ <strong>' . $seats_remaining . '</strong> seat';
        $output .= ($seats_remaining > 1 ? 's' : '') . ' remaining. Register below:';
        $output .= '</div>';

        $output .= do_shortcode(
            '[gravityform id="' . $registration_form_id . '" title="false" description="false" ajax="true"]'
        );
    }

    return $output;
});