Get contrast ratio between two UIColors

ContrastRatio.swift

// https://www.w3.org/TR/WCAG20/
// Contrast ratio
// Relative luminance

import UIKit

extension UIColor {
    convenience init(hex: UInt, alpha: CGFloat = 1) {
        self.init(red: CGFloat((hex & 0xff0000) >> 16) / 255,
                  green: CGFloat((hex & 0x00ff00) >> 8) / 255,
                  blue: CGFloat(hex & 0x0000ff) / 255,
                  alpha: alpha)
    }
}

private struct RGB {
    let red, green, blue: CGFloat
}

private extension RGB {
    init(color: UIColor) {
        let components: [CGFloat] = color.cgColor.components!
        self.init(red: components[0], green: components[1], blue: components[2])
    }
}

struct Luminance: RawRepresentable {
    let rawValue: CGFloat
}

extension Luminance {
    init(color: UIColor) {
        self.init(rgb: RGB(color: color))
    }

    private init(rgb: RGB) {
        func relativeLuminance(from value: CGFloat) -> CGFloat {
            value <= 0.03928 ? value / 12.92 : pow((value + 0.055) / 1.055, 2.4)
        }
        let red: CGFloat = relativeLuminance(from: rgb.red)
        let green: CGFloat = relativeLuminance(from: rgb.green)
        let blue: CGFloat = relativeLuminance(from: rgb.blue)
        rawValue = red * 0.2126 + green * 0.7152 + blue * 0.0722
    }
}

struct ContrastRatio: RawRepresentable {
    let rawValue: CGFloat
}

extension ContrastRatio {
    init(light: UIColor, dark: UIColor) {
        rawValue = (Luminance(color: light).rawValue + 0.05) / (Luminance(color: dark).rawValue + 0.05)
    }
}

let lightOrange: UIColor = .init(hex: 0xf8a23b)
let darkOrange: UIColor = .init(hex: 0xf18828)
ContrastRatio(light: lightOrange, dark: darkOrange).rawValue
// 1.2327559224150646