Game server dev swaps singletons for dependency injection and interfaces: because nothing future-proofs code like triple the boilerplate

A recent software development project has undergone a significant refactoring effort to adhere to the Dependency Inversion Principle, a key component of the SOLID principles of object-oriented design. The project's codebase was modified to ensure that higher-level modules depend on abstractions rather than concrete implementations of lower-level modules. Specifically, interfaces were created for manager classes, such as AuthManager and PlayerManager, to enable loose coupling and greater flexibility. The Service class was also refactored to inject dependencies, rather than relying on static variables. A Composition Root was established in the Server class, where managers, services, and handlers are created and injected. This refactoring effort aims to improve the project's maintainability and scalability, and is part of a broader effort to apply the SOLID principles to the codebase. The project's development is ongoing, with the next phase focusing on implementing in-game functionality.