Drupal 7 Übercart consecutive invoice number module

For the latest version of the übercart module in drupal 7, I need someone who can write a module that generates an invoice number for each order and allows to add this invoice number in the invoice template. The invoice numbers have to be consecutive, so the first order has invoice number 1, the second order has invoice number 2 and so on. When an order isn't completed, or an order is deleted, the remaining invoice numbers still need to be consecutive. So there can't be any gaps between invoice numbers.