Custom UIButton Drawing UIBezierPaths to CAShapeLayers and morph-animating them via CABasicAnimation

CameraButton.swift

//  CameraButton.swift
//  Created by Todd Hopkinson Aug 2016
//  UIButton approximating Apple's camera button appearance and appearance behavior 

import UIKit

enum CameraButtonMode {
    case VideoReady
    case VideoRecording
    case PhotoReady
}

class CameraButton: UIButton {
    
    var operationMode: CameraButtonMode = CameraButtonMode.PhotoReady
    
    private var diskLayer: CAShapeLayer!
    private var ringLayer: CAShapeLayer!
    private var roundRectCGPath: CGPath!
    private var diskCGPath: CGPath!
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        setupPaths()
    }
    
    required init(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)!
        setupPaths()
    }
    
    private func setupPaths() {
        
        let centerPoint = CGPoint(x: frame.size.width / 2.0, y: frame.size.height / 2.0)
        let diskPath = circlePathWithCenter(centerPoint, radius: (frame.size.width - 18)/2)
        diskCGPath = diskPath.CGPath
        let ringPath = UIBezierPath(arcCenter: CGPoint(x: frame.size.width / 2.0, y: frame.size.height / 2.0), radius: (frame.size.width - 10)/2, startAngle: 0.0, endAngle: CGFloat(M_PI * 2.0), clockwise: true)
        let roundRectPath = squarePathWithCenter(centerPoint, side: centerPoint.x/1.6)
        roundRectCGPath = roundRectPath.CGPath
        
        // Setup the ring layer
        ringLayer = CAShapeLayer()
        ringLayer.path = ringPath.CGPath
        ringLayer.lineWidth = 4.0
        ringLayer.strokeColor = UIColor.whiteColor().colorWithAlphaComponent(0.75).CGColor
        ringLayer.fillColor = UIColor.clearColor().CGColor
        ringLayer.strokeEnd = 1.0
        
        layer.addSublayer(ringLayer)
        
        // Setup the disk layer
        diskLayer = CAShapeLayer()
        diskLayer.path = diskPath.CGPath
        diskLayer.fillColor = UIColor.whiteColor().CGColor
        diskLayer.strokeColor = UIColor.clearColor().CGColor
        diskLayer.strokeEnd = 1.0
        
        // Add the diskLayer to the view's layer's sublayers
        layer.addSublayer(diskLayer)
    }
    
    private func circlePathWithCenter(center: CGPoint, radius: CGFloat) -> UIBezierPath {
        let circlePath = UIBezierPath()
        circlePath.addArcWithCenter(center, radius: radius, startAngle: -CGFloat(M_PI), endAngle: -CGFloat(M_PI/2), clockwise: true)
        circlePath.addArcWithCenter(center, radius: radius, startAngle: -CGFloat(M_PI/2), endAngle: 0, clockwise: true)
        circlePath.addArcWithCenter(center, radius: radius, startAngle: 0, endAngle: CGFloat(M_PI/2), clockwise: true)
        circlePath.addArcWithCenter(center, radius: radius, startAngle: CGFloat(M_PI/2), endAngle: CGFloat(M_PI), clockwise: true)
        circlePath.closePath()
        return circlePath
    }
    
    // TODO: make this square into a roundRect
    private func squarePathWithCenter(center: CGPoint, side: CGFloat) -> UIBezierPath {
        let squarePath = UIBezierPath()
        let startX = center.x - side / 2
        let startY = center.y - side / 2
        squarePath.moveToPoint(CGPoint(x: startX, y: startY))
        squarePath.addLineToPoint(squarePath.currentPoint)
        squarePath.addLineToPoint(CGPoint(x: startX + side, y: startY))
        squarePath.addLineToPoint(squarePath.currentPoint)
        squarePath.addLineToPoint(CGPoint(x: startX + side, y: startY + side))
        squarePath.addLineToPoint(squarePath.currentPoint)
        squarePath.addLineToPoint(CGPoint(x: startX, y: startY + side))
        squarePath.addLineToPoint(squarePath.currentPoint)
        squarePath.closePath()
        return squarePath
    }
    
    private func morphDiskToRoundRect() {
        let morph: CABasicAnimation = CABasicAnimation(keyPath: "path")
        morph.duration = 0.33
        morph.fromValue = diskCGPath
        morph.toValue = roundRectCGPath
        morph.removedOnCompletion = false
        morph.fillMode = kCAFillModeForwards
        diskLayer.addAnimation(morph, forKey: "morph disk to roundrect")
    }
    
    private func morphRoundRectToDisk() {
        let morph: CABasicAnimation = CABasicAnimation(keyPath: "path")
        morph.duration = 0.33
        morph.fromValue = roundRectCGPath
        morph.toValue = diskCGPath
        morph.removedOnCompletion = false
        morph.fillMode = kCAFillModeForwards
        diskLayer.addAnimation(morph, forKey: "morph roundrect to disk")
        
    }
    
    func updateButtonMode(mode: CameraButtonMode) {

        let previousMode = self.operationMode
        self.operationMode = mode
        
        switch mode {
        case .PhotoReady:
            // change disk color to white
            self.diskLayer.path = diskCGPath
            self.diskLayer.fillColor = UIColor.whiteColor().CGColor
            if previousMode == .VideoRecording {
                self.morphRoundRectToDisk()
            }
            break
        case .VideoReady:
            self.diskLayer.fillColor = UIColor.redColor().CGColor
            if previousMode == .VideoRecording {
                self.morphRoundRectToDisk()
            } else {
                self.diskLayer.path = diskCGPath
            }
            break
        case .VideoRecording:
            self.morphDiskToRoundRect()
            break
        }
    }
}