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interface Navigator {
  fun startUserDetail(login: String)
  fun showSettings()
}

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class App : Application()   
  override fun onCreate() {
    super.onCreate()
    registerActivityLifecycleCallbacks(analyticsCallbacks)
    registerActivityLifecycleCallbacks(pushCallbacks)
  }
  // other App code
}

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class App : Application() 
  override fun onCreate() {
    super.onCreate()
    appComponent.callbacks().forEach { registerActivityLifecycleCallbacks(it) }
  }
  // ... other App code
}

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@Module
class AnalyticsModule {

  @Provides
  @IntoSet
  fun analyticsCallbacks(callbacks: AnalyticsCallbacks): ActivityLifecycleCallbacks = callbacks
}

@Module
class PushModule {

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class PushCallbacks(
  val pushStream: PushStream
) : Application.ActivityLifecycleCallbacks, PushStream.OnPush {

  private var foregroundActivity: Activity? = null

  override fun onActivityResumed(activity: Activity) {
    foregroundActivity = activity
    pushStream.register(this)
  }

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interface PushStream {
  fun register(onPush: OnPush)
  fun unregister(onPush: OnPush)

  interface OnPush {
    fun onPush(push: PushMessage)
  }
}

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class App : Application()   
  override fun onCreate() {
      super.onCreate()
      registerActivityLifecycleCallbacks(analyticsCallbacks)
  }
  // ... other App code
}

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interface Analytics {
  fun activityCreated(activity: Activity)
  fun activityResumed(activity: Activity)
  fun activityPaused(activity: Activity)
  fun activityDestroyed(activity: Activity)
}

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class AnalyticsCallbacks(
  val analytics: Analytics
) : Application.ActivityLifecycleCallbacks {

  override fun onActivityCreated(activity: Activity, savedInstanceState: Bundle?) = analytics.activityCreated(activity)

  override fun onActivityResumed(activity: Activity) = analytics.activityResumed(activity)

  override fun onActivityPaused(activity: Activity) = analytics.activityPaused(activity)

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class ContactsViewModel(val getContactsUseCase: GetContactsUseCase, parameters: Parameters) : ViewModel() {
  private val contactsLiveData: LiveData<Contacts> by lazy {
    val liveData = MutableLiveData<Contacts>()
    getContactsUseCase.loadContacts(parameters) { liveData.value = it }
    return@lazy liveData
  }

  fun contacts(parameters: Parameters): LiveData<Contacts> = contactsLiveData
}