Aim towards a layered architecture using dependency inversion principle

[MattHag]

Is your feature request related to a problem? Please describe.
Adapting Solaar code or even starting to work on it is hard, and you likely introduce a bug. As is, a lot of hardware is required to verify functionality.

Describe the solution you'd like
Aim for an architecture, that's easy to test, maintain and extend.
It should be possible to implement a FakeDevice, which e.g. behaves like an MX Master 3S and supports hardware independent implementation and testing of new features, while ensuring, that existing functionality still works. Final tests require the actual hardware.

Aim for a three layered architecture, consisting of

• Presentation Layer
• Business Logic
• Database Layer

The business logic contains the most relevant code, we care about. It can be covered by unit tests, when applying the dependency inversion principle (DIP). The business logic should depend on abstractions (an interface), not on a specific implementation. This is achieved by explicitly passing an implementation which satisfies the interface, rather than hard coupling different components. This results in composition over inheritance.
It enables simple tests, without mocking and patching and simply passing a fake instead.

The (work in progress) gives a first insight on the proposed architecture. Parts of the code already satisfy the proposal, others need quite some work to move from inheritance to composition.

(Work in progress)

Describe alternatives you've considered
Stick with the untestable big ball of mud, as it was months ago.

Related tickets

• General cleanup of code #2273
• Settings: Refactor code to reduce complexity and dependencies #2659
• Persist rules: Use Repository Pattern to decouple implementation #2675

Relevant books
https://www.cosmicpython.com/book/chapter_01_domain_model.html

Information

• Solaar version: 1.1.13+