CALayer extension for using blocks instead of animation delegates

ClosureBasedCAAnimationDelegate.swift

//
//  CALayerExtensions.swift
//

import QuartzCore

internal typealias LayerAnimationBeginClosure = (CAAnimation) -> Void
internal typealias LayerAnimationCompletionClosure = (CAAnimation, Bool) -> Void

// MARK: LayerAnimationDelegate Class -

private class LayerAnimationDelegate: NSObject {
    
    var beginClosure: LayerAnimationBeginClosure?
    var completionClosure: LayerAnimationCompletionClosure?
    
    // MARK: - Protocol Implementations
    
    // MARK: CAAnimation (Informal)
    
    override func animationDidStart(animation: CAAnimation) {
        guard let beginClosure = beginClosure else { return }
        beginClosure(animation)
    }
    
    override func animationDidStop(animation: CAAnimation, finished: Bool) {
        guard let completionClosure = completionClosure else { return }
        completionClosure(animation, finished)
    }

}

// MARK: - CALayer Extension -

extension CALayer {

    // MARK: - Conveniences for Adding Animations
    
    func addAnimation(animation: CAAnimation) {
        addAnimation(animation, forKey: nil)
    }
    
    func addAnimation(animation: CAAnimation, forKey key: String?, completionClosure: LayerAnimationCompletionClosure?) {
        addAnimation(animation, forKey: key, beginClosure: nil, completionClosure: completionClosure)
    }
    
    func addAnimation(animation: CAAnimation, forKey key: String?, beginClosure: LayerAnimationBeginClosure?, completionClosure: LayerAnimationCompletionClosure?) {
        let animationDelegate = LayerAnimationDelegate()
        animationDelegate.beginClosure = beginClosure
        animationDelegate.completionClosure = completionClosure
        
        animation.delegate = animationDelegate
        
        addAnimation(animation, forKey: key)
    }
    
    func replaceAnimation(animation: CAAnimation, forKey key: String) {
        replaceAnimation(animation, forKey: key, beginClosure: nil, completionClosure: nil)
    }
    
    func replaceAnimation(animation: CAAnimation, forKey key: String, completionClosure: LayerAnimationCompletionClosure?) {
        replaceAnimation(animation, forKey: key, beginClosure: nil, completionClosure: completionClosure)
    }
    
    func replaceAnimation(animation: CAAnimation, forKey key: String, beginClosure: LayerAnimationBeginClosure?, completionClosure: LayerAnimationCompletionClosure?) {
        removeAnimationForKey(key)
        addAnimation(animation, forKey: key, beginClosure: beginClosure, completionClosure: completionClosure)
    }
    
}