Add IconImage to encapsulate our icon processing logic

Shared/Extensions/IconImage.swift

@@ -0,0 +1,66 @@
+//
+//  IconImage.swift
+//  NetNewsWire
+//
+//  Created by Maurice Parker on 11/5/19.
+//  Copyright © 2019 Ranchero Software. All rights reserved.
+//
+
+import Foundation
+import RSCore
+
+final class IconImage {
+	
+	lazy var isDark: Bool = {
+		return image.isDark()
+	}()
+	
+	let image: RSImage
+	
+	init(_ image: RSImage) {
+		self.image = image
+	}
+	
+}
+
+#if os(macOS)
+	extension NSImage {
+		func isDark() -> Bool {
+			return self.cgImage(forProposedRect: nil, context: nil, hints: nil)?.isDark() ?? false
+		}
+	}
+#else
+	extension UIImage {
+		func isDark() -> Bool {
+			return self.cgImage?.isDark() ?? false
+		}
+	}
+#endif
+
+extension CGImage {
+
+	func isDark() -> Bool {
+		guard let imageData = self.dataProvider?.data else { return false }
+		guard let ptr = CFDataGetBytePtr(imageData) else { return false }
+		
+		let length = CFDataGetLength(imageData)
+		var pixelCount = 0
+		var totalLuminance = 0.0
+		
+		for i in stride(from: 0, to: length, by: 4) {
+			
+			let r = ptr[i]
+			let g = ptr[i + 1]
+			let b = ptr[i + 2]
+			let luminance = (0.299 * Double(r) + 0.587 * Double(g) + 0.114 * Double(b))
+			
+			totalLuminance += luminance
+			pixelCount += 1
+			
+		}
+		
+		let avgLuminance = totalLuminance / Double(pixelCount)
+		return avgLuminance < 37.5
+	}
+	
+}

Shared/Extensions/RSImage-Extensions.swift

@@ -11,19 +11,19 @@ import RSCore
 
 extension RSImage {
 	
-	static let avatarSize = 48
+	static let maxIconSize = 48
 	
-	static func scaledForAvatar(_ data: Data, imageResultBlock: @escaping (RSImage?) -> Void) {
+	static func scaledForIcon(_ data: Data, imageResultBlock: @escaping (RSImage?) -> Void) {
 		DispatchQueue.global(qos: .default).async {
-			let image = RSImage.scaledForAvatar(data)
+			let image = RSImage.scaledForIcon(data)
 			DispatchQueue.main.async {
 				imageResultBlock(image)
 			}
 		}
 	}
 
-	static func scaledForAvatar(_ data: Data) -> RSImage? {
-		let scaledMaxPixelSize = Int(ceil(CGFloat(RSImage.avatarSize) * RSScreen.mainScreenScale))
+	static func scaledForIcon(_ data: Data) -> RSImage? {
+		let scaledMaxPixelSize = Int(ceil(CGFloat(RSImage.maxIconSize) * RSScreen.mainScreenScale))
 		guard var cgImage = RSImage.scaleImage(data, maxPixelSize: scaledMaxPixelSize) else {
 			return nil
 		}