precedencegroup HierarchyPrecedence {
    lowerThan: AssignmentPrecedence
    associativity: left
}
infix operator |--: HierarchyPrecedence


public protocol UIViewHierarchyProvider {
    associatedtype View: UIView
    var view: View { get }
    var viewController: UIViewController? { get }
    func append(_ view: UIView)
}
extension UIViewHierarchyProvider {
    
    @discardableResult
    public static func |-- <V:UIView> (lpred: Self, rpred: V) -> Self {
        lpred.append(rpred)
        return lpred
    }
    
    @discardableResult
    public static func |-- <V:UIView> (lpred: Self, rpred: V?) -> Self {
        guard let view = rpred else { return lpred }
        lpred.append(view)
        return lpred
    }

    @discardableResult
    public static func |-- <V:UIView> (lpred: Self, rpred: [V]) -> Self {
        for view in rpred { lpred.append(view) }
        return lpred
    }
    
    @discardableResult
    public static func |-- (lpred: Self, rpred: UIViewController) -> Self {
        guard let parent = lpred.viewController else { return lpred }
        parent.addChild(rpred)
        lpred.append(rpred.view)
        rpred.didMove(toParent: parent)
        return lpred
    }

}





public class UIViewHierarchy: UIViewHierarchyProvider {
    public let view:UIView
    public let viewController: UIViewController?
    init(_ view:UIView, viewController: UIViewController?) {
        self.view = view
        self.viewController = viewController
    }
    public func append(_ view: UIView) {
        self.view.addSubview(view)
    }
}

public class UIStackViewHierarchy: UIViewHierarchyProvider {
    public let view:UIStackView
    public let viewController: UIViewController?
    init(_ view:UIStackView, viewController: UIViewController?) {
        self.view = view
        self.viewController = viewController
    }
    public func append(_ view: UIView) {
        self.view.addArrangedSubview(view)
    }
}



extension UIView {
    @discardableResult
    public func hierarchy(in viewController: UIViewController? = nil, _ processer:(UIViewHierarchy)->Void) -> Self {
        let h = UIViewHierarchy(self, viewController: viewController)
        processer(h)
        return self
    }
}

extension UIStackView {
    @discardableResult
    public func arrangedHierarchy(in viewController: UIViewController? = nil, skipCleaning: Bool = false, _ processer:(UIStackViewHierarchy)->Void) -> Self {
        if !skipCleaning {
            while let view = self.subviews.first {
                view.removeFromSuperview()
            }
        }
        let h = UIStackViewHierarchy(self, viewController: viewController)
        processer(h)
        return self
    }
}

extension UIViewController {
    @discardableResult
    public func hierarchy(_ processer:(UIViewHierarchy)->Void) -> Self {
        let h = UIViewHierarchy(self.view, viewController: self)
        processer(h)
        return self
    }
}