mvvm.swift

// Lambda helper class
final class LambdaHelper {
    // AWS config constants, etc.
    private let lambdaInvoker: AWSLambdaInvoker!
    static let sharedInstance = LambdaHelper()

    private init() {
        // Set up AWS config, etc.
        lambdaInvoker = AWSLambdaInvoker.default()
    }

    func search(query: String) {
        let dictionary: [String: Any?] = ["query": query]
        return Single<[TrackInfo]>.create { single in
            self.lambdaInvoker.invokeFunction("fake_arn", jsonObject: dictionary) { (response, error) in
                // Response is a JSON Foundation object, so cast to JSON data
                guard error == nil,
                    let json = try? JSONSerialization.data(withJSONObject: response),
                    let results = try? JSONDecoder().decode([TrackInfo].self, from: response) else {
                    return single(.error(error ?? LambdaError.invalidResponse))
                }
                single(.success(results))
            }
            return Disposables.create()
        }
    }
}

// ViewModel
final class SearchViewModel {
    // Error driver omitted in this example
    var results: Driver<[TrackInfo]>

    init(lambdaHelper: LambdaHelper, queryTextObservable: Observable<String>) {
        results = queryTextObservable
            .distinctUntilChanged()
            .flatMap { query in
                return lambdaHelper.search(query).asObservable().materialize()
            }
            .elements()
            .asDriver(onErrorJustReturn: [])
    }
}

// View
class SearchViewController: UIViewController {
    // UITextField, etc.
    private let lambdaHelper = LambdaHelper.sharedInstance
    private let disposeBag = DisposeBag()
    private var viewModel: SearchViewModel?

    override func viewDidLoad() {
        super.viewDidLoad()

        viewModel = SearchViewModel(
            lambdaHelper: lambdaHelper,
            queryTextObservable: searchField.rx.text.orEmpty.asObservable(),
        )
        // VM results are to be used to drive a table view; for now, just subscribe
        viewModel?.results.asObservable().subscribe({ (event) in
            print(event)
        })
        .disposed(by: disposeBag)
    }
}