DemoProjects/NowPlayingView/NowPlayingView/ConnectionStatusIndicatorView.swift

import UIKit

/// Connection status view
class ConnectionStatusIndicatorView : UIView {
    
    enum State {
        case disconnected
        case connecting
        case connected
    }
    
    var state: State = .disconnected {
        didSet {
            self.setNeedsDisplay()
            if state == .connecting {
                if displayLink == nil {
                    let selector = #selector(setNeedsDisplay as () -> Void)
                    displayLink = CADisplayLink(target: self, selector:selector)
                }
                displayLink?.add(to: RunLoop.main, forMode: RunLoop.Mode.common)
            } else {
                displayLink?.remove(from: RunLoop.main, forMode: RunLoop.Mode.common)
                displayLink = nil;
            }
        }
    }
    
    var displayLink: CADisplayLink?
    
    override func didMoveToSuperview() {
        super.didMoveToSuperview()
        self.clearsContextBeforeDrawing = true;
        self.backgroundColor = UIColor.clear
    }
    
    override func draw(_ rect: CGRect) {
        guard let context = UIGraphicsGetCurrentContext() else {
            return
        }
        
        let size = self.bounds.size
        let path = CGPath(roundedRect: self.bounds, cornerWidth: size.width/2, cornerHeight: size.height/2, transform: nil)
        context.addPath(path)
        
        context.setFillColor(fillColor())
        context.fillPath()
    }
    
    private func timebasedValue() -> CGFloat {
        return CGFloat(abs(sin(Date().timeIntervalSinceReferenceDate*4)))
    }
    
    private func fillColor() -> CGColor {
        switch state {
        case .disconnected:
            return UIColor.red.cgColor
        case .connecting:
            return UIColor.orange.withAlphaComponent(0.5+timebasedValue()*0.3).cgColor
        case .connected:
            return UIColor.green.cgColor
        }
    }
}