Swift UIColor extension, that adds a contrast ratio function between two colors.

ContrastRatioSwift.swift

//
//  ContrastRatioSwift.swift
//  Contrast Ratio Swift
//
//  Created by João Santos on 25/05/2023.
//  Copyright © 2023 João Santos. All rights reserved.
//

import UIKit

extension UIColor {
    
    var luminance: CGFloat {
        let RED: CGFloat = 0.2126
        let GREEN: CGFloat = 0.7152
        let BLUE: CGFloat = 0.0722
        let GAMMA: CGFloat = 2.4
        
        var r: CGFloat = 0
        var g: CGFloat = 0
        var b: CGFloat = 0
        self.getRed(&r, green: &g, blue: &b, alpha: nil)
        
        let a = [r, g, b]
            .map({ v in
                return v <= 0.03928 ? v / 12.92 : pow((v + 0.055) / 1.055, GAMMA)
            })
        
        return a[0] * RED + a[1] * GREEN + a[2] * BLUE
    }
    
    func contrastTo(color: UIColor) -> CGFloat {
        let lum1 = self.luminance
        let lum2 = color.luminance
        let brightest = max(lum1, lum2)
        let darkest = min(lum1, lum2)
        return (brightest + 0.05) / (darkest + 0.05)
    }
    
    func hasEnoughContrast(toColor color: UIColor, forTextSize size: CGFloat = 16, weight: UIFont.Weight = .regular) -> Bool {
        let contrast = self.contrastTo(color: color)
        switch weight {
        case .medium, .semibold, .bold, .heavy, .black:
            return size >= 14 && contrast >= 3
        default:
            return contrast >= 4.5
        }
    }
}