Vending Machine Test

To run it 🚀

Just set the VendingMachine project as the startup one and run from VS.

Tech stack 💡

Frontend

• ReactJS

Backend

• .net core
• C#
• Swagger for API testing and documentation.

Goal 🎯

To have a virtual vending machine that would behave like a real one.

Strategy followed for backend 🗺️

To store the coins in the wallets, I injected singleton services which have the data they need so I don’t have to worry about the state of the coins.

Then for the products list, I simulated they are in a repository and implemented that in a way that if they end up being in a database, textfile or whatever it is easy to switch.

I built it in four layers:

1. API - holds the controllers and the DI configuration. Also Swagger was added to have a more readeable documentation accessing the /swagger endpoint. This layer references the Application & Domain layers.

2. Application - holds the services that run the logic of the application and communicate with the domain. Here’s where all the processing happen. This layer references the Domain layer.

3. Domain - holds the models and behavior definitions needed for the app to work.

4. Persistence - holds the implementation of the IProductRepository. This layer references the Application & Domain layers.

The project has essentially three models in the Domain layer:

1. Product - represents the Product entity and its behavior, in this case it has the ability to take itself and to substract the unit taken.

2. UserWalletService - represents the user's wallet and its behavior, keeps the collection of coins updated and handles them.

3. MachineWalletService - represents the vending-machine's wallet and it has the exact same behavior as the user's wallet, with the difference that the MachineWallet starts with a default amount of coins.

Each of these models has its service in the Application layer that handles them.

Additionally I added three custom exceptions to handle three validation scenarios:

1. InvalidCoinException - to avoid invalid coins to be inserted.

2. ProductNotAllowedException - to prevent for a product to be sold if the user has not entered an enough amount or if there’s no units left for the given product.

3. NoChangeExceptions - will happen if the vending machine has not enough coins to return the change.

Unit tests 🧪

Since both wallets are based on the same base-class, I built two sets of tests:

1. WalletTest.cs - Tests the functionality of the WalletService (coins and amount management), and since the user and the vending machine wallets implements the same logic, one is enough.

2. ProductsTest.cs - Tests the functionality of the ProductService to ensure that the listing and the Units management work as expected.

If I had more time I would have...

1. Added a logging to register exceptions and monitor.
2. Improved the flow for the method ProductsController.Take. I don't like having to worry about removing the coins from the machine wallet if it gets to this catch catch (NoChangeException ex).
3. Improved the UI, probably used Redux.