View Hierarchy Iterator

class UIView{
    var subViews : [UIView]
    var superView : UIView?
    var val : Character
    init(_ char: Character) {
        subViews = [UIView]()
        val = char
    }
}



let A = UIView("A")
let B = UIView("B")
let C = UIView("C")
let D = UIView("D")
let E = UIView("E")

let a = UIView("a")
let b = UIView("b")
let c = UIView("c")
let d = UIView("d")
let e = UIView("e")


d.subViews.append(e)
e.superView = d


D.subViews.append(E)
E.superView = D

a.subViews = [b,c,d]
b.superView = a
c.superView = a
d.superView = a


A.subViews = [B,C,D]

class viewIterator{

    var cur : UIView?

    init(_ rootView: UIView){
        cur = rootView
        moveChild()
    }

    private func moveChild(){
        guard let currV = cur else {
            return
        }
        var runner = currV
        while runner.subViews.count > 0 {
            runner = runner.subViews[0]
        }
        cur = runner
    }

    func hasNext() -> Bool{
        return cur != nil
    }
    func next() -> UIView?{
        guard let curView = cur else {
            return nil
        }
        let ans = curView

        if let superv = curView.superView {
            if let index = superv.subViews.firstIndex(where: { (view) -> Bool in
                view === cur
            }){
                if index == superv.subViews.count - 1 {
                    cur = superv
                }else{
                    cur = superv.subViews[index + 1]
                    moveChild()
                }
            }
        }else{
            cur = nil
        }
        return ans
    }
}



let iterator = viewIterator(a)

print(iterator.hasNext())
print(iterator.hasNext())
print(iterator.hasNext())
print(iterator.next()?.val)
print(iterator.next()?.val)
print(iterator.next()?.val)
print(iterator.next()?.val)
print(iterator.next()?.val)
print(iterator.next()?.val)