feat(ad-hoc): minor improvements (#346)

* Set `swiftLanguageVersions` in package spec
* Improve color lightness calculation

Package.swift

@@ -56,5 +56,6 @@ let package = Package(
                 .process("Resources")
             ]
         )
-    ]
+    ],
+    swiftLanguageVersions: [.v5]
 )

Sources/ProcessOutCoreUI/Sources/Core/UIKit+Extensions/UIColor+Brightness.swift

@@ -9,20 +9,45 @@ import SwiftUI
 
 extension UIColor {
 
+    func isLight(threshold: CGFloat = 0.5) -> Bool? {
+        perceptualLightness.map { $0 > threshold }
+    }
+
+    // MARK: - Private Methods
+
+    /// Returns the relative luminance of this color in range [0, 1].
+    ///
     /// - NOTE: Alpha is ignored
-    var brightness: CGFloat? {
-        let colorSpace = CGColorSpace(name: CGColorSpace.sRGB)! // swiftlint:disable:this force_unwrapping
-        let convertedColor = cgColor.converted(
-            to: colorSpace, intent: .defaultIntent, options: nil
-        )
+    private var perceptualLightness: CGFloat? {
+        guard let luminance else {
+            return nil
+        }
+        if luminance <= 0.008856 { // Based on CIE standard
+            return luminance * 9.033
+        }
+        return pow(luminance, 1 / 3) * 1.16 - 0.16
+    }
+
+    private var luminance: CGFloat? {
+        // swiftlint:disable:next force_unwrapping
+        let colorSpace = CGColorSpace(name: CGColorSpace.sRGB)!
+        let convertedColor = cgColor.converted(to: colorSpace, intent: .defaultIntent, options: nil)
         guard let components = convertedColor?.components, components.count >= 3 else {
             return nil
         }
-        // Calculation is based on this https://www.w3.org/WAI/ER/WD-AERT/#color-contrast
-        return (components[0] * 299 + components[1] * 587 + components[2] * 114) / 1000
+        // swiftlint:disable identifier_name
+        let r = linearValue(ofGammaEncoded: components[0])
+        let g = linearValue(ofGammaEncoded: components[1])
+        let b = linearValue(ofGammaEncoded: components[2])
+        // swiftlint:enable identifier_name
+        return 0.2126 * r + 0.7152 * g + 0.0722 * b
     }
 
-    func isLight(threshold: CGFloat = 0.5) -> Bool? {
-        brightness.map { $0 > threshold }
+    /// Convert a gamma encoded RGB to a linear value.
+    private func linearValue(ofGammaEncoded component: CGFloat) -> CGFloat {
+        if component <= 0.04045 {
+            return component / 12.92
+        }
+        return pow((component + 0.055) / 1.055, 2.4)
     }
 }