protocol State {
    var manager: AppUpdateManager { get }
    init(manager: AppUpdateManager)
}

protocol UpdateProcessControlling {
    func startUpdate()
    func postponeUpdate()
}


public class AppUpdateManager {

    var currentState: State

    init() {
        currentState = UpToDate(manager: self)
    }

    internal func transition<S>(to: S.Type) {
        currentState = S(manager: self)
    }

    public func startUpdate() {
        (currentState as? UpdateProcessControlling)?.startUpdate()
    }
}

// MARK: - UpToDate
struct UpToDate: State, UpdateProcessControlling {
    let manager: AppUpdateManager
    init(manager: AppUpdateManager) {
        self.manager = manager
    }

    func startUpdate() {
        // execute update logic etc.

        manager.transition(to: Updating.self)
    }

    func postponeUpdate() {
        // execute postponed logic  etc.

        manager.transition(to: Postponed.self)
    }
}

// MARK: - Updating
struct Updating: State {
    let manager: AppUpdateManager
    init(manager: AppUpdateManager) {
        self.manager = manager
    }
}

// MARK: - Postponed
struct Postponed: State {
    let manager: AppUpdateManager
    init(manager: AppUpdateManager) {
        self.manager = manager
    }
}