An extension on NSColor — offering initialization from and conversion to HEX string representations

NSColor+HexString.swift

//
// NSColor+HexString.swift
// 
// Created by Stephan Casas on 5/22/24.
//

import Foundation;
import AppKit;

extension NSColor {
    
    /// Create a new `NSColor` from the given string representation of a color's HEX or HEXA value.
    convenience init?(hexString: String){
        var hexString = hexString.starts(with: "#") ? String(hexString.trimmingPrefix("#")) : hexString;
        
        // Shorthand Format: #FFF
        if hexString.count == 3 {
            hexString = hexString.map({ "\($0)\($0)" }).joined()
        }
        
        // No-alpha Format: #FFFFFF
        if hexString.count == 6 {
            hexString = hexString.appending("FF");
        }
        
        // Should have full-alpha format by now.
        guard hexString.count == 8 else {
            return nil;
        }
        
        let rgbaValues = stride(from: 0, to: 7, by: 2).map({
            let lowerBound = hexString.index(hexString.startIndex, offsetBy: $0);
            let upperBound = hexString.index(after: lowerBound);
            return String(hexString[lowerBound...upperBound]);
        }).compactMap({
            Int($0, radix: 16)
        }).map({
            CGFloat($0) / 255
        });
        
        self.init(
            red: rgbaValues[0],
            green: rgbaValues[1],
            blue: rgbaValues[2],
            alpha: rgbaValues[3]);
    }
    
    /// Create a new string representation of this color's HEXA value.
    func toHexString() -> String {
        "#" + [
            self.redComponent,
            self.greenComponent,
            self.blueComponent,
            self.alphaComponent,
        ].map({
            UInt64($0 * 255)
        }).map({
            _uint64ToString($0, radix: 16, uppercase: true)
        }).joined()
    }
    
}