Keep track of animation in scenekit (swift) - swift

Question

I am trying to rotate a geometry on the right as long as I am touching the right side of the screen and left when touching the left side. When not touching the screen, the animation should stop.
For this I came up with the following code which works until I press again the screen and the geometry goes back to its original state instead of starting the rotatation from the previous position.
I also need to keep track of the angle for future development and node.rotation.w always returns 0.
func respondToLPGesture(gestureRecognize: UILongPressGestureRecognizer)
{
let scnView = self.view as SCNView
let spin = CABasicAnimation(keyPath: "rotation")
spin.duration = 2
spin.repeatCount = .infinity
let p = gestureRecognize.locationInView(scnView)
switch gestureRecognize.state
{
case .Began:
//Determine rotation direction
if p.x < scnView.frame.width / 2 {
//spin.fromValue = NSValue(SCNVector4: SCNVector4(x: 0, y: 0, z: 1, w: angle))
//spin.toValue = NSValue(SCNVector4: SCNVector4(x: 0, y: 0, z: 1, w: angle + 2*Float(M_PI)))
spin.byValue = NSValue(SCNVector4: SCNVector4(x: 0, y: 0, z: 1, w: 2*Float(M_PI)))
scnView.scene.rootNode.childNodes[1].addAnimation(spin, forKey: "spin around")
}
else {
spin.byValue = NSValue(SCNVector4: SCNVector4(x: 0, y: 0, z: 1, w: 2*Float(-M_PI)))
scnView.scene.rootNode.childNodes[1].addAnimation(spin, forKey: "spin around")
}
case .Ended:
println(scnView.scene.rootNode.childNodes[1].rotation.w) // Always returns 0.
scnView.scene.rootNode.childNodes[1].pauseAnimationForKey("spin around")
default:
println("Inside default")
}
}

Answer 1

Watching WWDC 2014 "What's New in SceneKit" helped me to find the answer.
To track a node position/rotation in Scenekit use "presentationNode".
Example below:
let angle = scnView.scene.rootNode.childNodes[1].presentationNode().rotation.w
Using the following will return the value of the targeted end of the animation which is always 0 in my code example:
let angle = scnView.scene.rootNode.childNodes[1].rotation.w