Update order status from custom status to another one based on date condition - 29/04/2018 14:56 EDT

Hello, I use woocommerce latest version and my clients pay either: 1) when they order (credit card, wire transfer, paypal,...) 2) with payment terms, so I ship the products and then I do a Direct debit at payment terms to get the funds. Once the order is shipped, its status is changed from "PROCESSING" to my custom status "SHIPPED". This update is done automatically by a tracking number plugin when I import the tracking numbers CSV file, so nothing to do here. I would like the following to happen automatically: 1) when order has already been paid, then the "SHIPPED" status should be automatically updated to "COMPLETED". So the condition can only depend of the payment gateway used (I will fill in the payment gateway IDs in the code you send me) since I manually change the 2) when order is paid at payment terms, then the order status should be automatically updated from "SHIPPED" to my other custom status "Processing direct debit" X days before the payment due date. I have in my order metas a custom meta "$due_date" with the payment due date, so you only need to get it. I need the code to add to my [login to view URL] file. I will fill in the payment gateway IDs - just let me know how to add several of them in the code for 1) Please let me know if you have any questions Thanks