What is the purpose of each architectural layer in an application?

Architectural layers help separate responsibilities, improve maintainability, and testability of the application.

• Presentation Layer: Responsible for displaying the user interface and interacting with it. It receives data from the Domain Layer and transforms it for presentation to the user. It sends user actions to the Domain Layer.
• Domain Layer: Contains the business logic of the application. It is independent of UI and infrastructure details. It includes entities, use cases, and repositories as interfaces.
  • Entities: Represent core business objects.
  • Use Cases (Interactors): Define interaction scenarios with the application. They orchestrate the work of repositories and entities to perform specific tasks.
  • Repositories (Interfaces): Define contracts for data retrieval and storage. Implementation resides in the Data Layer.
• Data Layer: Responsible for data retrieval and storage. It includes repository implementations, data sources, and data models.
  • Repository Implementations: Implement the repository interfaces defined in the Domain Layer.
  • Data Sources: Provide access to various data sources (API, local database, shared preferences, etc.).
  • Models (DTOs): Represent data formats used for communication with data sources. They differ from Entities in the Domain Layer.

Example of layer structure:

lib/
├── main.dart
├── presentation/
│   ├── widgets/
│   ├── pages/
│   ├── blocs/  // or other state management
├── domain/
│   ├── entities/
│   ├── usecases/
│   ├── repositories/
├── data/
│   ├── repositories/
│   ├── datasources/
│   ├── models/

Dependency scheme:

Presentation Layer -> Domain Layer <- Data Layer. (Data and Presentation depend on Domain, but Domain depends on no one).