Correct php script (random selection of file from folder)

Theres a php script. His task is to randomly select a file from a folder. And create a cookie, so that the next random does not coincide with the previous one.
As a result, it seems to work, but not incorrectly - not always pulled up the correct name of the file. correct.
Payment on readiness and check for Yandex/sber.
Start with random. And immediately specify the price/term with the telegrams.