ColorExporter

ColorExporter.swift

// ([^#\n]*)\s#([\dA-F]{6})
// (name: "$1", color: UIColor(hex: 0x$2)),
typealias NamedColor = (name: String, color: UIColor)

extension CGFloat {
    var prettyString: String {
        let formatter = NumberFormatter()
        formatter.numberStyle = .decimal
        formatter.roundingMode = .halfUp
        formatter.maximumFractionDigits = 10
        
        return formatter.string(from: NSNumber(value: Double(self)))!
    }
}

extension UIColor {
    
    var components: (red: CGFloat, green: CGFloat, blue: CGFloat, alpha: CGFloat) {
        var r: CGFloat = 0, g: CGFloat = 0, b: CGFloat = 0, a: CGFloat = 0
        getRed(&r, green: &g, blue: &b, alpha: &a)
        return (red: r, green: g, blue: b, alpha: a)
    }
    
    var colorLiteral: String {
        let (r, g, b, a) = components
        return "#colorLiteral(red: \(r.prettyString), green: \(g.prettyString), blue: \(b.prettyString), alpha: \(a.prettyString))"
    }
    
    convenience init(red: Int, green: Int, blue: Int) {
        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: 1.0)
    }
    
    convenience init(hex: Int) {
        self.init(red:(hex >> 16) & 0xff, green:(hex >> 8) & 0xff, blue:hex & 0xff)
    }
    
    var hexValue: String {
        let (r, g, b, a) = components
        
        guard a == 1 else { fatalError("Do not use semi-transparent colors") }
        
        let red     = Int(r * 255)
        let green   = Int(g * 255)
        let blue    = Int(b * 255)
        
        return String(format: "%02X%02X%02X", red, green, blue)
    }
}

func function(_ namedColor: NamedColor) -> String {
    return "    class var \(namedColor.name): UIColor { return \(namedColor.color.colorLiteral) } //#\(namedColor.color.hexValue)"
}

func export(colors: [NamedColor]) -> String {
    let header = "extension UIColor {\n"
    let functions = colors.map(function).joined(separator: "\n")
    let footer = "\n}"
    
    return [header, functions, footer].joined()
}