Activity Indicator with gradient circle

import UIKit

class ActivityIndicatorView: UIView {

    private lazy var gradientLayer: CAGradientLayer = {
        let gradient = CAGradientLayer()
        gradient.locations = [0.5, 1]
        gradient.startPoint = CGPointMake(0.0, 0.0)
        gradient.endPoint = CGPointMake(1.0, 0.8)
        gradient.anchorPoint = CGPointMake(0, 0)
        gradient.contentsScale = UIScreen.mainScreen().scale
        return gradient
    }()

    private lazy var circlePathLayer: CAShapeLayer = {
        let layer = CAShapeLayer()
        layer.fillColor = UIColor.clearColor().CGColor
        layer.strokeColor = UIColor.blackColor().CGColor
        layer.lineWidth = 3
        layer.anchorPoint = CGPointMake(0, 0)
        return layer
    }()
    
    var colors: [UIColor] = [UIColor.whiteColor(), UIColor.clearColor()]
    
    override init(frame: CGRect) {
        super.init(frame: frame)
    }
    
    convenience init(color: UIColor = UIColor.whiteColor()) {
        self.init(frame: CGRectZero)
        self.colors = [color, UIColor(hex: 0xffffff, alpha: 0)]
        setup()
    }
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        setup()
    }
    
    private func setup() {
        gradientLayer.colors = colors
        backgroundColor = UIColor.clearColor()
        gradientLayer.position = CGPoint(x: CGRectGetMidX(bounds), y: CGRectGetMidY(bounds))
        circlePathLayer.frame = gradientLayer.bounds
        gradientLayer.mask = circlePathLayer
        layer.addSublayer(gradientLayer)
    }
    
    override func layoutSubviews() {
        super.layoutSubviews()
        gradientLayer.colors = colors.map { $0.CGColor }
        circlePathLayer.path = UIBezierPath(roundedRect: CGRectInset(gradientLayer.bounds, 3, 3), cornerRadius: gradientLayer.bounds.size.width/2).CGPath
        gradientLayer.bounds = bounds
        rotate()
    }
    
    func rotate() {
        let rotation: CABasicAnimation = CABasicAnimation(keyPath: "transform.rotation.z")
        rotation.toValue = NSNumber(double: M_PI * 2)
        rotation.duration = 1
        rotation.cumulative = true
        rotation.delegate = self
        rotation.repeatCount = FLT_MAX
        self.layer.addAnimation(rotation, forKey: "rotationAnimation")
    }
    
    override func animationDidStop(anim: CAAnimation, finished flag: Bool) {
        
    }
    
}