Drupal Commerce - ability to close shop (restaurant/takeaway)
To do some flip-flopping with the Add to Cart buttons, take a look into the Commerce Stock module(s).  I'd imagine it's in the commerce simple stock.  When a product goes out of stock, it disables the Add to Cart button on the relevant product displays.  Though if even one product is available on that display, it won't disable it.  So, I would recommend checking out the commerce_stock.module and commerce_stock.rules.inc to see how they are doing that.

I envision a simple admin form page with a Close Store and Open Store buttons, and in their submit handlers, just running through and disabling the Add to Cart(s).  I'm sure there's a good way to do the "Restaurant Closed", "Restaurant Open" text, it's escaping me at the moment.