User case: change user role on PayPal webhooks

jfb-add-paypal-webhooks.php

<?php

/**
 * Hands up! If you are using version 1.1.0 or higher. You won't need the code below. Just use new events
 * @link https://user-images.githubusercontent.com/46720998/190651417-bba9c801-812c-4d8e-bbf4-d32075bc4fd7.png
 *
 *
 * 
 * This gist is an extended version of this gist.
 * @link https://gist.github.com/girafffee/040ff0ec2f148cd429d4a91cc7006c50#file-jfb-add-paypal-webhooks-php
 *
 * If your case involves a role change on confirmation/expiration of a subscription,
 * then you only need to copy 2 files from this (extended) gist.
 *
 * You must define your roles in the JET_FB_SUBSCRIPTION_ROLE and JET_FB_BASE_ROLE constants
 *
 * This example works on version 1.0.1
 */
 
const JET_FB_SUBSCRIPTION_ROLE = 'subscription_buyer';
const JET_FB_BASE_ROLE         = 'subscriber';

function jfb_add_paypal_webhooks( array $webhooks ) {
	require_once 'jfb-paypal-listen-subscription.php';

	$webhooks[] = new JFB_Paypal_Cancel_Subscription_Webhook();
	$webhooks[] = new JFB_Paypal_Expired_Subscription_Webhook();
	$webhooks[] = new JFB_Paypal_Suspend_Subscription_Webhook();
	$webhooks[] = new JFB_Paypal_Reactive_Subscription_Webhook();

	return $webhooks;
}

add_filter(
	'jet-form-builder/gateways/paypal/events',
	'jfb_add_paypal_webhooks'
);

jfb-paypal-listen-subscription.php

<?php

use Jet_FB_Paypal\Resources\Subscription;

class JFB_Paypal_Cancel_Subscription_Webhook extends \Jet_FB_Paypal\EventsHandlers\BillingSubscriptionCancelled {

	use JFB_Update_Role_On_Disable_Subscription;

	public function on_catch_event( $webhook_event ) {
		// Subscription status changes here
		$this->change_role( parent::on_catch_event( $webhook_event ) );
	}
}

class JFB_Paypal_Expired_Subscription_Webhook extends \Jet_FB_Paypal\EventsHandlers\BillingSubscriptionExpired {

	use JFB_Update_Role_On_Disable_Subscription;

	public function on_catch_event( $webhook_event ) {
		// Subscription status changes here
		$this->change_role( parent::on_catch_event( $webhook_event ) );
	}
}

class JFB_Paypal_Suspend_Subscription_Webhook extends \Jet_FB_Paypal\EventsHandlers\BillingSubscriptionSuspended {

	use JFB_Update_Role_On_Disable_Subscription;

	public function on_catch_event( $webhook_event ) {
		// Subscription status changes here
		$this->change_role( parent::on_catch_event( $webhook_event ) );
	}
}

class JFB_Paypal_Reactive_Subscription_Webhook extends \Jet_FB_Paypal\EventsHandlers\BillingSubscriptionActivated {

	use JFB_Update_Role_On_Disable_Subscription;

	public function on_catch_event( $webhook_event ) {
		// Subscription status changes here
		$this->change_role( parent::on_catch_event( $webhook_event ), JET_FB_SUBSCRIPTION_ROLE );
	}
}

trait JFB_Update_Role_On_Disable_Subscription {

	public function change_role( array $pair, $role = JET_FB_BASE_ROLE ) {
		/** @var Subscription $resource */
		list( $subscription, $resource ) = $pair;
		
		/** @var \WP_User|null */
		$user = $resource->get_user();

		if ( ! $user ) {
			return;
		}
		
		// Checking if a user has a role.
		if ( in_array( $role, (array) $user->roles, true ) ) {
			return;
		}

		$user->set_role( $role );
	}

}

Where to add this code. Will we add this code in fuction.php? Can you please give me a clear instruction?