Blends together two UIColors, returning a dynamic color

UIColor+Blended.swift

//
//  UIColor+Blended.swift
//
//  Created by Drew Olbrich on 5/16/21.
//  Copyright © 2021 Lunar Skydiving LLC. All rights reserved.
//
//  MIT License
//
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in all
//  copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
//

import UIKit

extension UIColor {
    
    /// Creates a dynamic color from the receiver blended with another color.
    ///
    /// If `weight` is 0, the color of `self` is returned. If `weight` is 1, the color
    /// of `otherColor` is returned.
    ///
    /// This method works correctly with light and dark mode. A dynamic color is
    /// returned, so if the user switches to dark mode, the dark mode versions of `self`
    /// and `otherColor` will be blended together and displayed.
    func blended(with otherColor: UIColor, weight: CGFloat) -> UIColor {
        func blend(_ baseColor: UIColor, with otherColor: UIColor, weight: CGFloat) -> UIColor {
            var red: CGFloat = 0
            var green: CGFloat = 0
            var blue: CGFloat = 0
            var alpha: CGFloat = 0
            baseColor.getRed(&red, green: &green, blue: &blue, alpha: &alpha)
            
            var otherRed: CGFloat = 0
            var otherGreen: CGFloat = 0
            var otherBlue: CGFloat = 0
            var otherAlpha: CGFloat = 0
            otherColor.getRed(&otherRed, green: &otherGreen, blue: &otherBlue, alpha: &otherAlpha)
            
            func mix(_ x: CGFloat, _ y: CGFloat, _ a: CGFloat) -> CGFloat {
                return (1 - a)*x + a*y
            }
            
            return UIColor(
                red: mix(red, otherRed, weight),
                green: mix(green, otherGreen, weight),
                blue: mix(blue, otherBlue, weight),
                alpha: mix(alpha, otherAlpha, weight)
            )
        }
        
        return UIColor(dynamicProvider: { traitCollection in
            var result: UIColor = .white
            traitCollection.performAsCurrent {
                result = blend(self, with: otherColor, weight: weight)
            }
            return result
        })
    }
        
}