Virtuemart - Custom Stock field in each attribute of product

When the admin creates a product will be able to set different number sizes for the specific shoe, and in each number size will set a unique stock number. So in the front-end if the user will buy the specific number from that shoes.. automatically the stock for this number size of the shoe will be -1. For example the user creates the shoe with name “Shoe01” and for that shoe sets the available numbers: Size: 41 Stock: 3 Size: 43 Stock: 1 SizeL 45 Stock 12 In the front-end a user buy the shoe01 and selects number 45, he pays.. and the order is completed. In the back-end the system is updated and the stock for Shoe01 is now: Size: 41 Stock: 3 Size: 43 Stock: 1 SizeL 45 Stock 11 (-1) Again a user buys the shoe01 – number 43, he pays…. In the back-end the system is updated and the stock for Shoe01 is now: Size: 41 Stock: 3 Size: 43 Stock: 0 (-1) SizeL 45 Stock 11 Because number 43 stock=0 that number must be no longer visible in the dropdown list in the front-end. That is the main idea!