UIColor+Hex.swift

import UIKit

extension UIColor {
    convenience init(red: Int, green: Int, blue: Int, a: Int = 255) {
        assert(red >= 0 && red <= 255, "Invalid red component")
        assert(green >= 0 && green <= 255, "Invalid green component")
        assert(blue >= 0 && blue <= 255, "Invalid blue component")

        self.init(
            red: CGFloat(red) / 255.0,
            green: CGFloat(green) / 255.0,
            blue: CGFloat(blue) / 255.0,
            alpha: CGFloat(a) / 255.0
        )
    }

    convenience init(rgb: Int) {
        self.init(
            red: (rgb >> 16) & 0xFF,
            green: (rgb >> 8) & 0xFF,
            blue: rgb & 0xFF
        )
    }

    convenience init(rgba: Int) {
        self.init(
            red: (rgba >> 24) & 0xFF,
            green: (rgba >> 16) & 0xFF,
            blue: (rgba >> 8) & 0xFF,
            a: rgba & 0xFF
        )
    }

    convenience init(gray: Int) {
        self.init(red: gray, green: gray, blue: gray)
    }

    func alpha(_ a: CGFloat) -> UIColor {
        let c = CIColor(cgColor: cgColor)
        return UIColor(red: c.red, green: c.green, blue: c.blue, alpha: a)
    }

    var isDarkColor: Bool {
        guard let rgb = cgColor.components else {
            return false
        }

        let rValue = 0.2126 * rgb[0]
        let gValue = 0.7152 * rgb[1]
        let bValue = 0.0722 * rgb[2]

        return (rValue + gValue + bValue) < 0.5
    }
}