Repository pattern with different strategies

repository.swift

// The object we will be fetching from local or remote data source
struct Note {
    var description: String
}

// Strategy
protocol NoteStrategy {
    func getNote(completion: @escaping (Note) -> Void)
}

// Local strategy
class LocalStrategy: NoteStrategy {
    
    func getNote(completion: @escaping (Note) -> Void) {
        
        // fetch person from your local storage
        let note = Note(description: "Note from local strategy")
        completion(note)
    }
    
    // to save the note to local storage
    func save(note: Note) { }
}

// Remote strategy
class RemoteStrategy: NoteStrategy {
    
    // local strategy for updating cache
    let localStrategy: LocalStrategy
    
    func getNote(completion: @escaping (Note) -> Void) {
        
        // fetch from backend
        let note = Note(description: "Note from remote strategy")
        completion(note)
        
        // save to your local stroage for caching purposes
        localStrategy.save(note: note)
    }
}

// If available strategy
class IfAvailableStrategy: NoteStrategy {
    
    // both strategies are listed here as we are dependent on both
    let localStrategy: LocalStrategy
    let remoteStrategy: RemoteStrategy
    
    func getNote(completion: @escaping (Note) -> Void) {
        localStrategy.getNote { note in
            if note == nil {
                return self.remoteStrategy.getNote(completion: completion)
            }
            completion(note)
        }
    }
}

// Repository
// You can add default value for strategy by using protocol extension
protocol NoteRepositoryProtocol {
    func getNote(with strategy: NoteStrategy, completion: @escaping (Note) -> Void)
}

// Our repository 🎉
class NoteRepository: NoteRepositoryProtocol {
    func getNote(with strategy: NoteStrategy, completion: @escaping (Note) -> Void) {
        strategy.getNote(completion: completion)
    }
}


// How to use it
var repository: NoteRepositoryProtocol

repository.getNote(with: LocalStrategy()) { note in
    print(note) // prints local note
}

repository.getNote(with: RemoteStrategy()) { note in
    print(note) // prints remote note
}

repository.getNote(with: IfAvailableStrategy()) { note in
    print(note) // prints local note
}