A basic blocker for WooCommerce that works on Groundhogg.io Tags

woocommerce-groundhogg-blocker.php

<?php

/*
 * Plugin Name: WooCommerce Customer Blocker for Groundhogg
 * Plugin URI:
 * Description: Block customers at the checkout using tags in Groundhogg
 * Version:  1.0
 * Author: Colin Longworth
 * Author URI: http://www.wooninja.io
 * Developer: Colin Longworth
 * Developer URI: http://www.wooninja.io
 * Text Domain: woocommerce-groundhogg-blocker
 * License: GPLv2
 *
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License, version 2, as
 *  published by the Free Software Foundation.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */

if (!defined('ABSPATH')) {
    exit;
}

use function Groundhogg\get_contactdata;
use function Groundhogg\is_a_contact;

class WooCommerce_Groundhogg_Blocker
{
    const WC_GH_BLOCK_TAG = "Banned";

    public function __construct()
    {
        add_action('woocommerce_after_checkout_validation', [$this, 'check_for_block_tags'], 10, 2);
    }

    /**
     * Validate the email at the checkout stage
     *
     * @param $fields
     * @param $errors
     */
    public function check_for_block_tags($fields, $errors)
    {
        $banned = false;

        /**
         * Check if logged in first
         */
        if (is_user_logged_in()) {

            $wp_user = wp_get_current_user();

            if ($this->validate_email($wp_user->user_email)) $banned = true;

        }

        /**
         * Check the billing email to avoid a logged in user avoiding the block
         */
        if (isset($fields['billing_email'])) {

            if ($this->validate_email($fields['billing_email']))$banned = true;

        }

        if($banned) $errors->add('validation', 'Please contact us by phone to place this order');
    }

    /**
     * Check if the given email is a GH contact AND if they are tagged to be blocked
     *
     * @param $email
     * @return bool
     */
    private function validate_email($email)
    {
        $contact = get_contactdata($email);

        if (is_a_contact($contact) && $contact->has_tag(self::WC_GH_BLOCK_TAG)) return true;

        return false;
    }

}

new WooCommerce_Groundhogg_Blocker();