WatchedFlow.swift

import RxFlow
import UIKit

class WatchedFlow: Flow {

    var root: UIViewController {
        return self.rootViewController
    }

    private let rootViewController = UINavigationController()
    private let service: MoviesService

    init(withService service: MoviesService) {
        self.service = service
    }

    func navigate(to step: Step) -> [NextFlowItem] {
        guard let step = step as? DemoStep else { return NextFlowItem.noNavigation }

        switch step {

        case .movieList:
            return navigateToMovieListScreen()
        case .moviePicked(let movieId):
            return navigateToMovieDetailScreen(with: movieId)
        case .castPicked(let castId):
            return navigateToCastDetailScreen(with: castId)
        default:
            return NextFlowItem.noNavigation
        }
    }

    private func navigateToMovieListScreen () -> [NextFlowItem] {
        let viewModel = WatchedViewModel(with: self.service)
        let viewController = WatchedViewController.instantiate(with: viewModel)
        viewController.title = "Watched"
        self.rootViewController.pushViewController(viewController, animated: true)
        return [NextFlowItem(nextPresentable: viewController, nextStepper: viewModel)]
    }

    private func navigateToMovieDetailScreen (with movieId: Int) -> [NextFlowItem] {
        let viewModel = MovieDetailViewModel(withService: self.service,
                                             andMovieId: movieId)
        let viewController = MovieDetailViewController.instantiate(with: viewModel)
        viewController.title = viewModel.title
        self.rootViewController.pushViewController(viewController, animated: true)
        return [NextFlowItem(nextPresentable: viewController, nextStepper: viewModel)]
    }

    private func navigateToCastDetailScreen (with castId: Int) -> [NextFlowItem] {
        let viewModel = CastDetailViewModel(withService: self.service,
                                            andCastId: castId)
        let viewController = CastDetailViewController.instantiate(with: viewModel)
        viewController.title = viewModel.name
        self.rootViewController.pushViewController(viewController, animated: true)
        return NextFlowItem.noNavigation
    }
}