how_unit_testing_can_help_write_better_designs_7.swift

final class MovieManager: MovieManaging {

    let client: ClientProtocol

    let store: KeyValueStoring

    init(client: ClientProtocol, store: KeyValueStoring) {
        self.client = client
        self.store = store
    }

    /// Fetches popular movies from the server, then stores them.
    func getPopularMovies(_ completion: @escaping (Result<[Movie], MovieManagerError>) -> Void) {

        client.get(path: "/movies/popular") { (result: Result<[Movie], MovieManagerError>) in
            switch result {
            case .success(let movies):

                for movie in movies {
                    self.store.set(value: movie, for: movie.id)
                }

                completion(.success(movies))

            case .failure(let error):
                // handles error...
                completion(.failure(error))
            }
        }
    }

    /// Fetches a movie from the store if it exists, from the server otherwise.
    func getMovie(id movieID: String, completion: @escaping (Result<Movie, MovieManagerError>) -> Void) {

        store.getValue(for: movieID) { (result: Result<Movie?, KeyValueStoreError>) in
            switch result {
            case .success(.some(let storedMovie)):
                completion(.success(storedMovie))

            case .success(.none):
                client.get(path: "/movies/\(movieID)") { (result: Result<[Movie], ClientError>) in
                    switch result {
                    case .success(let movie):
                        self.store.set(value: movie, for: movie.id)
                        completion(movie)

                    case .failure(let error):
                        completion(.failure(.client(error)))
                    }
                }

            case .failure(let error):
                completion(.failure(.store(error)))
            }
        }
    }
}