Reserve a slot

This django app shall allow for N amount of items within the app to be reserved by people. It should allow for me to set the amount of items to be set and people to reserve the slots. For example, if I want to make 10 items available for purchase and 20 of each item available, the app should put each user into a "countdown bucket" that will countdown while the user has the option to purchase the item. If they don't purchase the item their item will be returned to "general population" and become available for someone else to purchase. This project should be done within Django. I will provide models for my shop if necessary. Here is a basic example: Item 1: 20 qty Item 2: 20 qty Item 3: 20 qty Users will rush to the site to purchase Item 1 or item 2 and watch the decrease in qty in real time. When there are no available quantity left the item will say "SOLD OUT". The quantity amount should be able to be set in the django admin panel. Users should only be able to reserve a single slot. Once the users have a slot for multiple items reserved, they will be directed to "checkout" through braintree. Further information available upon request.