final class AnimationView: UIView {
    private let shapeLayer: CAShapeLayer = {
        let it = CAShapeLayer()
        it.fillColor = UIColor.clear.cgColor
        it.strokeColor = UIColor(hex: 0xFF598B).cgColor
        it.lineWidth = 5
        it.lineCap = .round
        it.strokeEnd = 0
        return it
    }()

    private let trackLayer: CAShapeLayer = {
        let it = CAShapeLayer()
        it.fillColor = UIColor.clear.cgColor
        it.strokeColor = UIColor(hex: 0xDDDDDD).cgColor
        it.lineWidth = 5
        it.lineCap = .round
        return it
    }()

    override func draw(_ rect: CGRect) {
        let center = CGPoint(x: bounds.width / 2, y: bounds.height / 2)

        let circlePath = UIBezierPath(arcCenter: center,
                                      radius: 100,
                                      startAngle: -.pi / 2,
                                      endAngle: .pi * 3 / 2,
                                      clockwise: true)

        [trackLayer, shapeLayer].forEach { layer in
            layer.path = circlePath.cgPath
            self.layer.addSublayer(layer)
        }
    }

    func startAnimation() {
        let anim = CABasicAnimation(keyPath: "strokeEnd")
        anim.fromValue = 0
        anim.toValue = 1
        anim.duration = 1
        anim.isRemovedOnCompletion = false
        anim.fillMode = .forwards
        shapeLayer.add(anim, forKey: "key")
    }
}