At what level of architecture is the repository layer usually implemented?

The repository layer in Android architecture is usually implemented at the domain layer or data layer.

Its task is to abstract access to data sources (databases, network, cache) and provide a convenient interface for business logic.

For example, in MVVM architecture, the repository is located between the ViewModel and data sources. It encapsulates the logic of retrieving and saving data.

An example of a repository interface:

interface UserRepository {
    suspend fun getUser(userId: String): User
    suspend fun saveUser(user: User)
}

Implementation can use Room for local database and Retrofit for network requests, combining data and deciding where to fetch it from.