SingleResponsibility.swift

protocol LoginInteractorInput {
   func doLogin(login: String, password: String) -> Bool
}

protocol LoginRouterInput {
   func openMainScreen()
}

class LoginInteractor: LoginInteractorInput {
  
   func doLogin(login: String, password: String) -> Bool {
      // TODO: - Make Network Request
      
      return true
   }
  
}

class LoginRouter: LoginRouterInput {
  
   func openMainScreen() {
      // TODO: - Instantiate Main ViewController and show it
   }
  
}

class LoginPresenter {
   
   var interactor: LoginInteractorInput!
   var router: LoginRouterInput!
  
   init(interactor: LoginInteractorInput, router: LoginRouterInput) {
      self.interactor = interactor
      self.router = router
   }
  
   // MARK: - Logic
   func login() {
      let login = "login"
      let password = "password"
     
      guard login.isEmpty, password.isEmpty else {
         return
      }
     
      if interactor.doLogin(login: login, password: password) {
         router.openMainScreen()
      }
   }
  
}

let router = LoginRouter()
let interactor = LoginInteractor()
let presenter = LoginPresenter(interactor: interactor, router: router)