I want automatic discount function in invoices at Item level
I have 800 items in my warehouse. Every item has different discount function.

Item (A)
basic rate 80
if customer buys 1 to 3 then I will apply 2% discount.
if customer buys 3 to12 then i will apply 5% discount
if more then 12 then 7% discount

Item (B)
basic rate 200
if customer buys 1 to 8 then I will apply 10% discount.
if customer buys 8 to15 then i will apply 12% discount
if more then 15 then 15% discount

Item (C)
basic rate 80
if customer buys 1 to 10 then I will apply 6% discount.
if customer buys 10 to 20 then i will apply 8% discount
if more then 20 then 12% discount

Item (D) , 794 items more....
means combination of quantity range and discount % may very for every item.
so I want function in which I only need to add quantity discount will be applied automatically.

then at invoice level I give cash discount in % it can be 1, 2 or more
I give discount at both item level and invoice level.