protocol PIPWUsable {
    var initialState: PIPWState { get }
    var initialPosition: PIPWPosition { get }
    var pipEdgeInsets: UIEdgeInsets { get }
    var pipSize: CGSize { get }
    var pipShadow: PIPWShadow? { get }
    var pipCorner: PIPWCorner? { get }
    func didChangedState(_ state: PIPWState)
    func didChangePosition(_ position: PIPWPosition)
}

open class PIPWKit {
    
    static var isActive: Bool { return floatingWindow != nil }
    static var isPIP: Bool { return state == .pip }

    static var floatingWindow: PIPWViewWindow?
    static var mainWindow: UIWindow?

    class func show(with viewController: UIViewController, mainWindow: UIWindow? = nil, completion: (() -> Void)? = nil) { ... }
    class func dismiss(animated: Bool, completion: (() -> Void)? = nil) { ... }
}

func setNeedUpdatePIPSize()
func startPIPMode()
func stopPIPMode()

class PIPViewController: UIViewController, PIPWUsable {
    
    var initialState: PIPWState { return .pip }
    var pipSize: CGSize { return CGSize(width: 200.0, height: 200.0) }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .blue
        view.layer.borderColor = UIColor.red.cgColor
        view.layer.borderWidth = 1.0
    }
    
    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
        super.touchesEnded(touches, with: event)
        
        if PIPWKit.isPIP {
            PIPWKit.floatingWindow?.stopPIPMode()
        } else {
            PIPWKit.floatingWindow?.startPIPMode()
        }
    }
    
    func didChangedState(_ state: PIPWState) {
        switch state {
        case .pip:
            print("PIPViewController.pip")
        case .full:
            print("PIPViewController.full")
        }
    }
}

let vc = PIPViewController()
PIPWKit.show(with: vc)
PIPWKit.dismiss(animated: true)

class PIPViewController: UIViewController, PIPWUsable {

    func onUpdatePIPSize(_ sender: UIButton) {
        pipSize = CGSize(width: 100 + Int(arc4random_uniform(100)),
                         height: 100 + Int(arc4random_uniform(100)))
        PIPWKit.floatingWindow?.setNeedUpdatePIPSize()
    }
}

class PIPViewController: UIViewController, PIPWUsable {

    func fullScreenAndPIPMode() {
        if PIPWKit.isPIP {
            PIPWKit.floatingWindow?.stopPIPMode()
        } else {
            PIPWKit.floatingWindow?.startPIPMode()
        }
    }

    func didChangedState(_ state: PIPWState) {}
    func didChangePosition(_ position: PIPWPosition) {}
}