/**
 * Create a new customer.
 *
 * @param  string $email    Customer email.
 * @param  string $username Customer username.
 * @param  string $password Customer password.
 * @param  array  $args     List of arguments to pass to `wp_insert_user()`.
 * @return int|WP_Error Returns WP_Error on failure, Int (user ID) on success.
 */
function wc_create_new_customer( $email, $username = '', $password = '', $args = array() ) {
    if ( empty( $email ) || ! is_email( $email ) ) {
        return new WP_Error( 'registration-error-invalid-email', __( 'Please provide a valid email address.', 'woocommerce' ) );
    }

    if ( email_exists( $email ) ) {
        // REMOVED: return new WP_Error( 'registration-error-email-exists', apply_filters( 'woocommerce_registration_error_email_exists', __( 'An account is already registered with your email address. <a href="#" class="showlogin">Please log in.</a>', 'woocommerce' ), $email ) );

        $user = get_user_by( 'email', $email ); // ADDED
        return $user->ID; // ADDED

    }

    if ( 'yes' === get_option( 'woocommerce_registration_generate_username', 'yes' ) && empty( $username ) ) {
        $username = wc_create_new_customer_username( $email, $args );
    }

    $username = sanitize_user( $username );

    if ( empty( $username ) || ! validate_username( $username ) ) {
        return new WP_Error( 'registration-error-invalid-username', __( 'Please enter a valid account username.', 'woocommerce' ) );
    }

    if ( username_exists( $username ) ) {
        return new WP_Error( 'registration-error-username-exists', __( 'An account is already registered with that username. Please choose another.', 'woocommerce' ) );
    }

    // Handle password creation.
    $password_generated = false;
    if ( 'yes' === get_option( 'woocommerce_registration_generate_password' ) && empty( $password ) ) {
        $password           = wp_generate_password();
        $password_generated = true;
    }

    if ( empty( $password ) ) {
        return new WP_Error( 'registration-error-missing-password', __( 'Please enter an account password.', 'woocommerce' ) );
    }

    // Use WP_Error to handle registration errors.
    $errors = new WP_Error();

    do_action( 'woocommerce_register_post', $username, $email, $errors );

    $errors = apply_filters( 'woocommerce_registration_errors', $errors, $username, $email );

    if ( $errors->get_error_code() ) {
        return $errors;
    }

    $new_customer_data = apply_filters(
        'woocommerce_new_customer_data',
        array_merge(
            $args,
            array(
                'user_login' => $username,
                'user_pass'  => $password,
                'user_email' => $email,
                'role'       => 'customer',
            )
        )
    );

    $customer_id = wp_insert_user( $new_customer_data );

    if ( is_wp_error( $customer_id ) ) {
        return $customer_id;
    }

    do_action( 'woocommerce_created_customer', $customer_id, $new_customer_data, $password_generated );

    return $customer_id;
}