Align views

extension UIView{
    func align(_ anchor : Anchor, to siblingView: UIView) -> UIView{
        switch anchor {
        case .leading:
            self.frame.origin.x = siblingView.frame.origin.x
        case .trailing:
            self.frame.origin.x = siblingView.frame.origin.x + siblingView.frame.width - self.frame.width
        case .top:
            self.frame.origin.y = siblingView.frame.origin.y
        case .botton:
            self.frame.origin.y = siblingView.frame.origin.y + siblingView.frame.height - self.frame.height
        case .centerX:
            self.center.x = siblingView.center.x
        case .centerY:
            self.center.y = siblingView.center.y
        }
        return self
    }
}


enum Anchor {
    case leading
    case top
    case botton
    case centerX
    case centerY
    case trailing
}




/*

 - align view if they are not at same view hierarchy。
 > 总体思路就是 要移动那个， 就把另一个的坐标系变成这个要动的
 ```swift
 */
extension UIView{

    func alignWithDifferentCoordinate(_ anchor : Anchor, to siblingView: UIView) -> UIView{
        //move self, so convert siblingView's frame to self's coordinate
        let rect = siblingView.convert(siblingView.bounds, to: self.superview)  //-> 这里siblingView bound 就是siblingView自己把自己当坐标系
        switch anchor {
        case .leading:
            self.frame.origin.x = rect.origin.x
        case .trailing:
            self.frame.origin.x = rect.origin.x + rect.width - self.frame.width
        case .top:
            self.frame.origin.y = rect.origin.y
        case .botton:
            self.frame.origin.y = rect.origin.y + rect.height - self.frame.height
        case .centerX:
            self.center.x = rect.origin.x + rect.width / 2
        case .centerY:
            self.center.y = rect.origin.y + rect.height / 2
        }

        return self
    }
}