4.1.x hook needed for Commerce

So I'm in need of a plugin/hook that will allow me to discount purchases depending on how may items are purchased of that specific item to a specific price currently there a feature that discounts the next item purchased for like a bogo but will not discount all the items just the next one after the said limit. Let me know what you think if the existing code could be changed for that or of it would be easier to add new code for this. Thanks for reading.