play with vc hierarchy

vc_hierarchy.swift

import UIKit


protocol Action {}

struct ConcreteAction1 : Action {}

struct ConcreteAction2 : Action {}

enum ActionError : ErrorType {
    case NoHandler
}

protocol UIViewControllerActionHandler : class {
    func handleAction(action: Action) -> Bool
}

extension UIViewController {
    
    func handlerOfType<T>(type: T.Type) -> T {
        var tmp : UIViewController? = self
        while let viewController = tmp {
            if let handlerCandidate = viewController as? T {
                return handlerCandidate
            }
            tmp = viewController.parentViewController
        }
        fatalError()
    }
    
    func emitAction(action: Action) {
        var tmp : UIViewController? = self
        while let viewController = tmp {
            if let handlerCandidate = viewController as? UIViewControllerActionHandler
                where handlerCandidate.handleAction(action) {
                return
            }
            tmp = viewController.parentViewController
        }
        fatalError()
    }
}

protocol ConcreteAction1Handler : class, UIViewControllerActionHandler {
    func handleAction(action: ConcreteAction1) -> Bool
}

protocol ConcreteAction2Handler : class, UIViewControllerActionHandler {
    func handleAction(action: ConcreteAction2) -> Bool
}

class ContentController : UIViewController {
    init(_ handler1: ConcreteAction1Handler, _ handler2: ConcreteAction2Handler) {
        super.init(nibName: nil, bundle: nil)
    }
    
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

class RootFlowController : UIViewController {}

extension RootFlowController : ConcreteAction1Handler {
    func handleAction(action: ConcreteAction1) -> Bool {
        print("action1 handled")
        return true
    }
    
    func handleAction(action: Action) -> Bool {
        if let ca = action as? ConcreteAction1 { return handleAction(ca) }
        return false
    }
    
    func returnFlowController() -> FlowController {
        let flowController = FlowController(
            self.handlerOfType(ConcreteAction1Handler)
        )
        self.addChildViewController(flowController)
        flowController.didMoveToParentViewController(self)
        return flowController
    }
}

class FlowController : UIViewController {
    
    init(_ handler: ConcreteAction1Handler) {
        super.init(nibName: nil, bundle: nil)
    }
    
    required init?(coder aDecoder: NSCoder) { fatalError("init(coder:) has not been implemented") }
    
    func returnContentController() -> ContentController {
        let concreteController = ContentController(
            self.handlerOfType(ConcreteAction1Handler),
            self.handlerOfType(ConcreteAction2Handler)
        )
        self.addChildViewController(concreteController)
        concreteController.didMoveToParentViewController(self)
        return concreteController
    }

    
}

extension FlowController : ConcreteAction2Handler {
    
    func handleAction(action: ConcreteAction2) -> Bool {
        print("action2 handled")
        return true
    }
    
    func handleAction(action: Action) -> Bool {
        if let action = action as? ConcreteAction2 { return handleAction(action) }
        return false
    }
    
}


let rootFlowController = RootFlowController()
let flowController = rootFlowController.returnFlowController()

let concreteController = flowController.returnContentController()

concreteController.emitAction(ConcreteAction1())
concreteController.emitAction(ConcreteAction2())