Automatically assign new user_email and restrict update after first login - wordpress

Question

How can I automatically assign a new email to a user in WordPress AND restrict any further update after the first login ?
For example setting the email to the following structure:
{user_id}#example.com
I've tried a few things but couldn't figure it out, any help is appreciated.
I wrote this code, but only users whose email has been registered, their email has been edited, other people who have not registered email, no email has been registered for them. How do I solve this?
my code:
add_action ('admin_head','set_auto_mail');
function set_auto_mail() {
$users = get_users(array('fields'=>'all'));
foreach($users as $user){
$user = get_userdata($user->ID);
if ( in_array( 'subscriber', (array) $user->roles ) ) {
$mail = ($user->ID)."#example.com";
if($mail!=' ') wp_update_user( array ('ID' => $user->ID, 'user_email' => $mail) );
else wp_update_user( array ('ID' => $user->ID, 'user_email' => $user->user_email) );
if($user->user_email == '')
wp_update_user( array ('ID' => $user->ID, 'user_email' => $user->user_email) );
}
}
}

Answer 1

This should do exactly what you wanted.
We set a new user meta data called is_new_user which we will use later on to detect if this is the first ever login for a specific user.
We set a hook to update the user_email on first time login and we update is_new_user to specify that this isn't a new user anymore. Like that we prevent permanent update on login.
Then we fire up the necessary functions to disable email updates. Visually and from the backend for all non-new users.
I'm using first_name, las_name and ID for the email structure. Output:
$first_name.$last_name$ID#bogus.com
<?php
/**
* Adds meta data is_new_user to a user, which let us detect new users on first login.
*
* Fires immediately after a new user is registered.
*
* #link https://developer.wordpress.org/reference/hooks/wp_login/
*/
add_action( 'user_register', 'wpso66983605_add_user_meta_is_new_user' );
function wpso66983605_add_user_meta_is_new_user( $user_id ) {
add_user_meta( $user_id, 'is_new_user', 1, true );
};
/**
* Update user email on first login.
*
* Fires after the user has successfully logged in.
*
* #link https://developer.wordpress.org/reference/hooks/wp_login/
*/
add_action( 'wp_login', 'wpso66983605_set_user_email_on_first_login', 10, 2 );
function wpso66983605_set_user_email_on_first_login( $user_login, $user ) {
if ( ! get_user_meta( $user->ID, 'is_new_user', true ) ) {
return;
};
if ( get_user_meta( $user->ID, 'is_new_user', true ) ) {
update_user_meta( $user->ID, 'is_new_user', 0, 1 );
$userdata = array (
'ID' => $user->ID,
'user_email' => sanitize_email( sanitize_title_with_dashes( $user->first_name . '.' . $user->last_name . $user->ID) . '#bogus.com' ),
);
wp_update_user( $userdata );
};
};
/**
* Prevent users from changing their email address
*
* Modified to ONLY fire when a user is considered as non-new user (user has already made at least 1 login).
*
* #link https://wordpress.stackexchange.com/a/363376/190376
*/
if ( ! class_exists( 'DisableMailChange' ) ) {
class DisableMailChange {
public function __construct() {
add_action( 'personal_options_update', array( $this, 'disable_mail_change_BACKEND' ), 5 );
add_action( 'show_user_profile', array( $this, 'disable_mail_change_HTML' ) );
}
public function disable_mail_change_BACKEND( $user_id ) {
if ( ! get_user_meta( get_current_user_id(), 'is_new_user', true ) ) {
if ( ! current_user_can( 'manage_options' ) ) {
$user = get_user_by( 'id', $user_id );
$_POST['email'] = $user->user_email;
};
};
}
public function disable_mail_change_HTML( $user ) {
if ( ! get_user_meta( get_current_user_id(), 'is_new_user', true ) ) {
if ( ! current_user_can( 'manage_options' ) ) {
echo '<script>document.getElementById("email").setAttribute("disabled","disabled");</script>';
};
};
}
};
new DisableMailChange();
};