TCA+UINavigationController.swift

// Simple example of the reducer where Destination is a screen that is pushed onto the UINavigationController viewControllers stack

struct AppFeature: Reducer {

    enum Destination: Equatable, Identifiable {
        case screenA(ScreenA.State)
        case screenB(ScreenB.State)
        case screenC(ScreenC.State)
        
        var id: String {
            switch self {
            case let .screenA(state):
                return state.id
            case let .screenB(state):
                return state.id
            case let .screenC(state):
                return state.id
            }
        }
    }

    struct State: Equatable {
        var route: IdentifiedArrayOf<Destination> = .init()
    }
    
    enum Action: Equatable {
        case route(_ id: String, _ destination: Destination)
    }
    
    
    var body: some ReducerProtocol<State, Action> {
        Reduce { state, action in
            switch action {
            case .route:
                return .none
            }
        }
    }
}

// UINavigationController

class DestinationNavigationController: UINavigationController {
    let store: StoreOf<AppFeature>
    let viewStore: ViewStoreOf<AppFeature>
    
    private var routeCancellable: AnyCancellable?
    
    init(store: StoreOf<AppFeature>) {
        self.store = store
        self.viewStore = ViewStore(store, observe: { $0 })
    }
    
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        routeCancellable = viewStore
                                .publisher
                                .route
                                .sink { (route: [AppFeature.Destination]) in
                                    // Given the array of destinations, we need to be able to scope
                                    // the StoreOf<AppFeature> down in to child stores. With the child stores,
                                    // (ie. StoreOf<PlaceReducer>, StoreOf<ListReducer>), we will be expected
                                    // to return a UIViewController for it.
                                    
                                    // NOTE: We will only ever be pushing, popping, or setting view controllers on the stack
                                    // so there is no need to worry about presenting view controllers, sheets, etc.
                                }
    }
}