Is zakat obligatory on a restaurant's total revenue (income) or on its net profit, keeping in mind that the purchases do not remain for a full hawl (lunar year)?

The Zakat of trade pertains to goods prepared for sale and is not obligatory on shop fixtures. Upon the completion of a hawl (a lunar year), the goods prepared for sale are appraised at their current value, and the existing cash and outstanding debts are added to this value. Then, Zakat is paid at a rate of one-quarter of one-tenth (2.5%) of the total. The hawl begins from the ownership of the original capital used to purchase the goods. Even if the goods themselves have not been owned for a full hawl, the money continuously cycles between goods, cash, and debts, and Zakat becomes obligatory on all of it upon the completion of the hawl.