Some useful algorith

Generate unique username based on email
$username = sanitize_user( current( explode( '@', $email ) ), true );

    // Ensure username is unique.
    $append     = 1;
    $o_username = $username;

    while ( username_exists( $username ) ) {
        $username = $o_username . $append;
$append++;
    }

// Handle password creation.
if ( 'yes' === get_option( 'woocommerce_registration_generate_password' ) && empty( $password ) ) {
$password           = wp_generate_password();
$password_generated = true;
} elseif ( empty( $password ) ) {
return new WP_Error( 'registration-error-missing-password', __( 'Please enter an account password.', 'woocommerce' ) );
} else {
$password_generated = false;
}