Add a custom meta field value to WooCommerce order if status changes to custom status

I have searched all over the internet. What I’m looking for is to create a custom woocommerce order field which will be automatically added to the order when order status changes to wc-kurzuhradena which the custom order status, with the value of current month and year. Example value: May 2021

So far I have this code which adds a custom field but I need to find a solution for a date when this status has been updated.

function add_date_field_shipped() {
  global $woocommerce, $post;
  $order = new WC_Order($post->ID);

   if ( empty(get_post_meta( $post->ID, 'shipped', true)) && ('kurzuhrada' == $order->status)) {
    update_post_meta( $post->ID, 'shipped', 'value here',true);
  }
}
add_action( 'pre_get_posts', 'add_date_field_shipped' );

Thank you in advance for help.

Answer

For a custom order status you can use woocommerce_order_status_{$status_transition[to]} composite action hook, where you will replace {$status_transition[to]} by the custom status slug.

So you get:

function action_woocommerce_order_status_kurzuhradena( $order_id, $order ) {
    // Set your default time zone (http://php.net/manual/en/timezones.php)
    // Set your locale information (https://www.php.net/manual/en/function.setlocale.php)
    date_default_timezone_set( 'Europe/Brussels' );
    setlocale( LC_ALL, 'nl_BE' );
    
    // Get current month & year
    $month = strftime( '%B' );
    $year = strftime( '%Y' );
    
    // Update meta
    $order->update_meta_data( 'shipped_date', $month . ' ' . $year );
    
    $order->save();
}
add_action( 'woocommerce_order_status_kurzuhradena', 'action_woocommerce_order_status_kurzuhradena', 10, 2 );

---

To allow this only once, when changing to custom order status, use:

function action_woocommerce_order_status_kurzuhradena( $order_id, $order ) {
    // Set your default time zone (http://php.net/manual/en/timezones.php)
    // Set your locale information (https://www.php.net/manual/en/function.setlocale.php)
    date_default_timezone_set( 'Europe/Brussels' );
    setlocale( LC_ALL, 'nl_BE' );
    
    // Get meta (flag)
    $flag = $order->get_meta( 'shipped_date_flag' );

    // NOT true
    if ( ! $flag ) {
        // Set flag
        $flag = true;
        
        // Update meta
        $order->update_meta_data( 'shipped_date_flag', $flag );
        
        // Get current month & year
        $month = strftime( '%B' );
        $year = strftime( '%Y' );
        
        // Update meta
        $order->update_meta_data( 'shipped_date', $month . ' ' . $year );       
    }
    
    // Save
    $order->save();
}
add_action( 'woocommerce_order_status_kurzuhradena', 'action_woocommerce_order_status_kurzuhradena', 10, 2 );