Make a discount on every third product in the woocommerce receipt?

Must be implemented when counting the goods in the shopping cart,
that every third product was with a 50% discount (3,6,9,12,15 product, etc.)
The discount should be sorted from larger to smaller.
The cheapest product is selected and it must be assigned a 50% discount.

The site is made on wordpress, woocommerce.

You need a php developer who knows how to work with webhook