Hi everyone

we buy product "A". ( "A" can NOT sell, can NOT manufacturing, can Purchase)

Transform "A" to "B". ("B" can NOT sell,  can manufacturing, can NOT purchase)

Transform "B" to "C". ("C" can sell, can manufacturing, can NOT purchase)

we are selling Only "C".

we don't make "C" before order that. first we get order from customer, then make "B" and then make "C".

I want allow to sell "C" only when we have "A" enough On-Hand. if we don't have "A" then don't allow to sell "C".