The models

Let's create some models before we start with any visual part for the app. First, add a new file called Supply.swift. Here, we are going to create a class that represents some supplies, which can be of the drink, food, and dessert types. To differentiate them, we are going to create an enumeration called SupplyType:

enum SupplyType:String{
    case Drink = "drink", Food = "food", Dessert = "dessert"
}

Tip

You can create enumerations nested in a class; however, this kind of implementations still have some limitations. Therefore, it is still considered to be a better idea while implementing it independently.

Now, we need to create the Supply class. In this class, we need an attribute for the supply's name, another one for its type, and two private attributes to control its duration. We will also create a method to consume such supplies and another one to estimate when they are going to end. Remember that their duration is based on the time we need to consume the supply, not on their...