Generate a username during checkout for user [Paid Memberships Pro]

generate-username-from-email-pmpro.php

<?php
/**
 * Generate a username at PMPro checkout from email for users.
 * Hide your 'username' field using custom CSS.
 * Add this code to your site by following this guide - https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */

function my_pmpro_generate_username_at_checkout() {

	// Make sure PMPro is installed and the function to get the level at checkout exists.
	if ( ! function_exists( 'pmpro_getLevelAtCheckout' ) ) {
		return;
	}
	
	// check for level as well to make sure we're on checkout page
	if ( empty( pmpro_getLevelAtCheckout() ) ) {
		return;
	}
	
	if ( ! empty( $_POST['bemail'] ) ) {
		$_REQUEST['username'] = $_POST['username'] = my_pmpro_generate_username_from_email( $_POST['bemail'] );
	}
	
	if ( ! empty( $_GET['bemail'] ) ) {
		$_REQUEST['username'] = $_GET['username'] = my_pmpro_generate_username_from_email( $_GET['bemail'] );
	}

}
add_action( 'init', 'my_pmpro_generate_username_at_checkout' );

/**
 * Hide the username field on checkout.
 */
function my_pmpro_unset_required_username_checkout( $pmpro_required_user_fields ) {
	unset( $pmpro_required_user_fields['username'] );
	return $pmpro_required_user_fields;
}
add_filter( 'pmpro_required_user_fields', 'my_pmpro_unset_required_username_checkout', 10, 2 );


/**
 * Generate a username from a user's email address.
 * Helper function.
 */
function my_pmpro_generate_username_from_email( $email ) {

	$parts = explode( '@', $email );

	while ( username_exists( $parts[0] ) ) {
		$parts[0] .= random_int( 0, 9999 );
	}

	return sanitize_text_field( $parts[0] );
}

This recipe is included in the blog post on "Customizing Usernames on Your Membership Site" at Paid Memberships Pro here: https://www.paidmembershipspro.com/customizing-usernames-for-your-membership-site/