Link WooCommerce guest orders to existing customer account and create account if no user matches order billing email

sync-users-orders.php

<?php
// Make sure to allow a sufficient amount of ram to load all orders in memory
define('WP_MEMORY_LIMIT', '512M');

// Load WordPress core & plugins
require_once('wp-load.php');

// Get all completed orders
$query = new WC_Order_Query([
    'type' => 'shop_order',
    'status' => 'completed',
    'limit' => -1
]);
$orders = $query->get_orders();

foreach($orders as $order) {
    // If order is not linked to a customer account
    if (empty($order->get_customer_id())) {
        // First check if the customer has an email
        // if not, proceed to next order (cannot create account w/o email)
        if (empty($order->get_billing_email())) continue;

        // Echo current order id to cli
        echo 'Linking order to user account for order: ' . $order->get_id() . "\n";

        // Check if account exist for order billing email
        $user = get_user_by('email', $order->get_billing_email());

        // If an account matches, just link order to exiting user account
        if (!empty($user)) {
            wc_update_new_customer_past_orders($user->ID);
            continue;
        }

        /** Otherwise, create a new user account **/

        // Generate a random password
        $random_password = wp_generate_password();

        // Create new user with email as username & random passwd
        $user_id = wp_create_user($order->get_billing_email(), $random_password, $order->get_billing_email());

        // Update account w/ order billing details
        update_user_meta($user_id, 'billing_address_1', $order->get_billing_address_1());
        update_user_meta($user_id, 'billing_address_2', $order->get_billing_address_2());
        update_user_meta($user_id, 'billing_city', $order->get_billing_city());
        update_user_meta($user_id, 'billing_company', $order->get_billing_company());
        update_user_meta($user_id, 'billing_country', $order->get_billing_country());
        update_user_meta($user_id, 'billing_email', $order->get_billing_email());
        update_user_meta($user_id, 'billing_first_name', $order->get_billing_first_name());
        update_user_meta($user_id, 'billing_last_name', $order->get_billing_last_name());
        update_user_meta($user_id, 'billing_phone', $order->get_billing_phone());
        update_user_meta($user_id, 'billing_postcode', $order->get_billing_postcode());
        update_user_meta($user_id, 'billing_state', $order->get_billing_state());

        // Update account w/ order shipping details
        update_user_meta($user_id, 'shipping_address_1', $order->get_shipping_address_1());
        update_user_meta($user_id, 'shipping_address_2', $order->get_shipping_address_2());
        update_user_meta($user_id, 'shipping_city', $order->get_shipping_city());
        update_user_meta($user_id, 'shipping_company', $order->get_shipping_company());
        update_user_meta($user_id, 'shipping_country', $order->get_shipping_country());
        update_user_meta($user_id, 'shipping_first_name', $order->get_shipping_first_name());
        update_user_meta($user_id, 'shipping_last_name', $order->get_shipping_last_name());
        update_user_meta($user_id, 'shipping_method', $order->get_shipping_method());
        update_user_meta($user_id, 'shipping_postcode', $order->get_shipping_postcode());
        update_user_meta($user_id, 'shipping_state', $order->get_shipping_state());

        // Link order to newly created account
        wc_update_new_customer_past_orders($user_id);
    }
}