Stock aware client

[norbeta]

Feature or Bug?

• Feature
• Bug

Feature

With regards to issue #43 - make the client stock-aware.

What would you like?

Instead of being unable to complete the sale if stock=0, item stock should be checked when added to the cart.
Also, if item is out of stock before a sale - the item should be grayed out.

An override function should be implemented as well to not let the customer have to wait until someone with access to the server are able to update the stock.