LastFM Browser Demo

• The app retrieves the list of top artists from LastFM.
• Selecting an artist from the list displays a new list of similar artists.

To run the app you will need to provide a LastFM API key in Settings -> LastFM. Naturally, API key is not required to run unit tests as they rely on mocks.

Architecture

The project demonstrates a version of VIP/Clean Architecture approach to the app architecture design. Unlike variations of MVC/MVVM this covers the entire architecture of the app, not just the interactions with UI layer. Another notable difference is a much clearer separation between roles of a layer (module) and a model wherein models are passed across layers' boundaries. The design ensures decoupling, testability, extendability, all those good things. Abstraction is the corner stone of the design as no modules reference each other as concrete types even within a single scene/screen.

Here is how it works.

• AppScene protocol is the composition root responsible for instantiation and wiring of all the modules in the scene including injection of a service dependency.
• View Controller represents the View layer. It holds strong references to Interactor and Router
  • View Controller asks Interactor to perform a task within the scene, optionally passing a Request Model.
  • View Controller asks Router to navigate to another scene.
• Interactor holds strong references to Service and Presenter.
  • Interactor interprets a request and sends it to the Service.
  • After getting back data from the Service, Interactor passes Model to Presenter.
• Presenter only holds a weak reference to the View. It translates the Model to View Model and passes it onto the View.
• Router knows the concrete type the next scene will be built off, but relies on abstraction to delegate creation of the new scene to the composition root. Router only holds a weak reference to the View to trigger UIKit navigation events.

Service layer

The app pulls data from two sources/services: via LastFM API and from a local cache.

• On successful API request the service updates the cache and the UI.
• If data from the server comes in first, the cache response is ignored.
• If API request fails, the cached data will be displayed if already present in the cache.