What is the purpose of using clean architecture in application development?

Clean Architecture is used to achieve the following goals:

1. Framework Independence: The application's business logic does not depend on specific UI frameworks, databases, or external services. This allows for easy replacement of these components without significant changes to the core of the application.
2. Testability: By separating business logic from implementation details (UI, database), unit and integration logic are easier to isolate and test.
3. UI Independence: Data presentation and user interaction are separated from the use case logic, simplifying adaptation of the application to different platforms (Mobile, Web, Desktop) or UI changes.
4. Database Independence: The logic for saving and retrieving data is separated from business rules, making it easy to change the database or use different storage for various parts of the application.
5. External Agent Independence: Interaction with external systems (API, third-party services) is encapsulated in separate layers, minimizing their impact on business logic.

The structure typically includes layers:

• Entities: Contain the application's business rules. The innermost layer.
• Use Cases (Interactors): Describe specific user interactions with the application. Contain application-specific business logic.
• Interface Adapters (Presenters, Controllers, Gateways): Transform data between Use Cases and external agents (UI, DB, API).
• Frameworks & Drivers: External layer containing implementation details (UI frameworks, databases, web services, etc.).

Dependency principle: Dependencies are always directed inward, from outer layers to inner layers.