Генерация уникальных рандомных купонов
https://gdebrauwer.dev/blog/generating-unique-voucher-codes/
https://gdebrauwer.dev/blog/generating-unique-voucher-codes/
Günther Debrauwer
Generating unique, random-looking voucher codes
Generating one voucher code is easy, but what if you need to generate thousands (or millions) and you need to be sure that each voucher code is unique?
