LKBoundsDidChangeAction.swift

class LKBoundsDidChangeAnimation : CABasicAnimation {
    @objc var bounds : CGRect = CGRect.zero
    
    override func copy(with zone: NSZone? = nil) -> Any {
        let result = super.copy(with: zone)
        if let action = result as? Self {
            action.bounds = bounds
            return action
        }
        return result
    }
}

class LKBoundsDidChangeAction : CAAction {
    var pendingAnimation : LKBoundsDidChangeAnimation
    
    init(fromBounds: CGRect) {
        let rootContextKey = keyPath(\LKLabelLayer.currentBoundsDidChangeAnimation)
        let animation = LKBoundsDidChangeAnimation(keyPath:
            keyPath(rootContextKey, suffix: keyPath(\LKBoundsDidChangeAnimation.bounds)))
        animation.fromValue = fromBounds
        animation.duration = UIView.inheritedAnimationDuration > 0 ? UIView.inheritedAnimationDuration : 
                                                                     CATransaction.animationDuration()
        animation.bounds = fromBounds
        animation.timingFunction = CAMediaTimingFunction(name: .easeInEaseOut)
        pendingAnimation = animation
    }
    
    func run(forKey event: String, object anObject: Any, arguments dict: [AnyHashable : Any]?) {
        guard let textLayer = anObject as? LKLabelLayer, event == keyPath(\LKLabelLayer.bounds) else { return }
        if !pendingAnimation.bounds.equalTo(textLayer.bounds) {
            pendingAnimation.toValue = textLayer.bounds
            textLayer.add(pendingAnimation, forKey:keyPath(\LKBoundsDidChangeAnimation.bounds))
        }
    }
}

class LKCompositeAction : CAAction {
    var actions : [CAAction]
    init(actions: [CAAction]) {
        self.actions = actions
    }
    
    func run(forKey event: String, object anObject: Any, arguments dict: [AnyHashable : Any]?) {
        actions.forEach { (action) in
            action.run(forKey: event, object: anObject, arguments: dict)
        }
    }
}