francescobonizzi/lastminute-interview

lastminute.com interview project

lastminute.com interview project

To complete the interview project I chose C# as programming language and the .NET Core framework. I made this choice because I'm familiar with C# and the .NET Core framework is cross-platform.

The project structure

• SalesTaxes-Library: it contains all the application domain and logic. I defined a ShoppingCart as the Article(s) container and a ShoppingCartEditor with the taxes and totals calculation logic. I also imagined some abstractions: a ShopConfiguration and ShoppingCart(s) providers, with the idea the they could be implemented by persisted storage classes. It is cross-platform library, so it could be reused with other clients, for example a website. Lastly, it manages the Receipt rendering as an HTML page.
• SalesTaxes-Library-UnitTests: this is the unit tests project. I tested the interview given inputs and outputs, the shopping cart add/remove items method, and the method I defined to implement the rounding rule.
• SalesTaxes-ClientConsole: this is the client, the starting point of the whole application. This project depends on SalesTaxes-Library. When started, it runs the three IInterviewInput to generate the receipts and show their output.

Dependencies management

Since I feel it is important to rely on abstractions and decouple the application dependencies, I decided to initialize the application with a DI container. I chose Castle Windsor, a very popular DI library. Inside SalesTaxes-ClientConsole project I defined every dependency with their own lifestyle into the DependenciesInstaller class. To automate the registration of the InterviewInput(s) components I let this classes implement a dummy interface: IInterviewInput.

Data choices

• To represent currency amounts I chose the .NET decimal data type, because it is more suitable for financial calculations. Compared to floating-point types, has more precision on small numbers (which is our case).
• To categorize each article type, I defined the enum ArticleTypes.
• To apply the tax application rules I chose a lookup structure (a Dictionary) to associate each ArticleTypes to a tax percentage.

Continuous Integration

As a CI tool I chose GitHub Actions. I defined a configuration file, .github/workflows/dotnet-core.yml with some steps and conditions to build the repository projects:

• Trigger: every push or pull request on main branch
• Running OS: Ubuntu last version
• Actions:
  • Setup a .NET Core environment
  • Restore the external dependencies
  • Build every project with Release configuration
  • Run all tests
• The workflow run is successful if every step is succesful

Receipt rendering

To print the Receipt output I decided to make an HTML page - a template - with its own css style and a little portion of javascript code to fill it. The presentation layer of the application generates a Receipt object from a ShoppingCart object, serializes it as JSON and loads it into the receipt-template.html. Relying on receipt-template-loading.js, the template gets populated with the Receipt data. The javascript little methods also check for errors and prints them to the receipt rendered page if any. At the end of the process, the client starts a browser instance to show the result.

In the javascript code, you'll notice a method called setOrHideIfEmpty. I chose to hide a property value if empty with the idea that a receipt output could be very configurable, so that an hypothetical customer could choose to not show some receipt details.

A video of the result

Output 1

Output 2

Output 3