CatFacts Recruitment Task

Simple ASP.NET Core Web API created as a recruitment task.

The application retrieves a random cat fact from:

https://catfact.ninja/fact

Each retrieved response is appended as a new line to a local .txt file.

Technologies

• .NET 10
• ASP.NET Core Web API
• Dependency Injection
• HttpClientFactory
• xUnit
• Moq

Endpoint

GET /api/catfacts

Example response:

{
  "fact": "Cats sleep for around 16 hours a day.",
  "length": 41
}

Each response is also appended to:

CatFacts.Api/data/catfacts.txt

Configuration

The external API URL, timeout and file path are stored in appsettings.json.

Example:

{
  "CatFactApi": {
    "BaseUrl": "https://catfact.ninja/",
    "TimeoutSeconds": 10
  },
  "FileStorage": {
    "Path": "data/catfacts.txt"
  }
}

Running the project

dotnet restore
dotnet build
dotnet run --project CatFacts.Api

Then call:

GET /api/catfacts

Tests

Run tests with:

dotnet test

The project contains a unit test for CatFactService using Moq.

Technical decisions

• HttpClientFactory is used for communication with the external API.
• CancellationToken is propagated through the request flow.
• SemaphoreSlim protects concurrent writes to the local file.
• ILogger<T> is used for structured logging.
• IExceptionHandler and ProblemDetails provide centralized error handling.
• Configuration values are stored in appsettings.json.

The project intentionally does not use CQRS, MediatR, a database or additional architectural layers because they are not required for this small use case.