Adds UIColor.adjustedForDisplay() to display illegible tint colors

Adjusts illegible tint colors so that they can be displayed in the UI, e.g. by making them brighter or darker.

AltStore/Extensions/UIColor+AltStore.swift

@@ -12,3 +12,51 @@ extension UIColor
 {
     static let altBackground = UIColor(named: "Background")!
 }
+
+extension UIColor
+{
+    private static let brightnessMaxThreshold = 0.85
+    private static let brightnessMinThreshold = 0.35
+    
+    private static let saturationBrightnessThreshold = 0.5
+    
+    var adjustedForDisplay: UIColor {
+        guard self.isTooBright || self.isTooDark else { return self }
+        
+        return UIColor { traits in
+            var hue: CGFloat = 0
+            var saturation: CGFloat = 0
+            var brightness: CGFloat = 0
+            guard self.getHue(&hue, saturation: &saturation, brightness: &brightness, alpha: nil) else { return self }
+            
+            brightness = min(brightness, UIColor.brightnessMaxThreshold)
+            
+            if traits.userInterfaceStyle == .dark
+            {
+                // Only raise brightness when in dark mode.
+                brightness = max(brightness, UIColor.brightnessMinThreshold)
+            }
+            
+            let color = UIColor(hue: hue, saturation: saturation, brightness: brightness, alpha: 1.0)
+            return color
+        }
+    }
+    
+    var isTooBright: Bool {
+        var saturation: CGFloat = 0
+        var brightness: CGFloat = 0
+        
+        guard self.getHue(nil, saturation: &saturation, brightness: &brightness, alpha: nil) else { return false }
+        
+        let isTooBright = (brightness >= UIColor.brightnessMaxThreshold && saturation <= UIColor.saturationBrightnessThreshold)
+        return isTooBright
+    }
+    
+    var isTooDark: Bool {
+        var brightness: CGFloat = 0
+        guard self.getHue(nil, saturation: nil, brightness: &brightness, alpha: nil) else { return false }
+                
+        let isTooDark = brightness <= UIColor.brightnessMinThreshold
+        return isTooDark
+    }
+}