SpinView.swift

class SpinView: UIView {
    private var animating: Bool = false
    
    private func spin(with options: UIViewAnimationOptions) {
        // this spin completes 360 degrees every 2 seconds
        UIView.animate(withDuration: 0.5, delay: 0, options: options, animations: {() -> Void in
            self.transform = self.transform.rotated(by: .pi / 2)
        }, completion: {(_ finished: Bool) -> Void in
            if finished {
                if self.animating {
                    self.spin(with: .curveLinear)
                } else if options != .curveEaseOut {
                    // Last spin with easeOut
                    self.spin(with: .curveEaseOut)
                }
            }
        })
    }
    
    func startSpin() {
        if !animating {
            animating = true
            spin(with: .curveEaseIn)
        }
    }
    
    func stopSpin() {
        animating = false
    }
}