Animate reader view button

iOS/Article/ArticleExtractorButton.swift

@@ -0,0 +1,78 @@
+//
+//  ArticleExtractorButton.swift
+//  NetNewsWire-iOS
+//
+//  Created by Maurice Parker on 9/24/19.
+//  Copyright © 2019 Ranchero Software. All rights reserved.
+//
+
+import UIKit
+
+enum ArticleExtractorButtonState {
+	case error
+	case animated
+	case on
+	case off
+}
+
+class ArticleExtractorButton: UIButton {
+
+	var buttonState: ArticleExtractorButtonState = .off {
+		didSet {
+			if buttonState != oldValue {
+				switch buttonState {
+				case .error:
+					stripSublayer()
+					setImage(AppAssets.articleExtractorError, for: .normal)
+				case .animated:
+					setImage(nil, for: .normal)
+					setNeedsLayout()
+				case .on:
+					stripSublayer()
+					setImage(AppAssets.articleExtractorOn, for: .normal)
+				case .off:
+					stripSublayer()
+					setImage(AppAssets.articleExtractorOff, for: .normal)
+				}
+			}
+		}
+	}
+	
+	override func layoutSubviews() {
+		super.layoutSubviews()
+		guard case .animated = buttonState else {
+			return
+		}
+		stripSublayer()
+		addAnimatedSublayer(to: layer)
+	}
+	
+	private func stripSublayer() {
+		if layer.sublayers?.count ?? 0 > 1 {
+			layer.sublayers?.last?.removeFromSuperlayer()
+		}
+	}
+	
+	private func addAnimatedSublayer(to hostedLayer: CALayer) {
+		let image1 = AppAssets.articleExtractorOffTinted.cgImage!
+		let image2 = AppAssets.articleExtractorOnTinted.cgImage!
+		let images = [image1, image2, image1]
+		
+		let imageLayer = CALayer()
+		let imageSize = AppAssets.articleExtractorOff.size
+		imageLayer.bounds = CGRect(x: 0, y: 0, width: imageSize.width, height: imageSize.height)
+		imageLayer.position = CGPoint(x: bounds.midX, y: bounds.midY)
+		
+		hostedLayer.addSublayer(imageLayer)
+		
+		let animation = CAKeyframeAnimation(keyPath: "contents")
+		animation.calculationMode = CAAnimationCalculationMode.linear
+		animation.keyTimes = [0, 0.5, 1]
+		animation.duration = 2
+		animation.values = images as [Any]
+		animation.repeatCount = HUGE
+		
+		imageLayer.add(animation, forKey: "contents")
+	}
+	
+}