Resolve dynamic colors on macOS and iOS.

OSColor.swift

import SwiftUI

// MARK: - macOS

#if os(macOS)

typealias OSColor = NSColor

extension OSColor {
  func resolvedOSColor(colorScheme: ColorScheme? = nil) -> OSColor {
    var currentCGColor: CGColor = cgColor
    let appearance: NSAppearance? = {
      guard let colorScheme else {
        return nil
      }
      return NSAppearance(named: colorScheme == .dark ? .darkAqua : .aqua)
    }()

    (appearance ?? NSAppearance.currentDrawing()).performAsCurrentDrawingAppearance {
      currentCGColor = cgColor
    }

    return OSColor(cgColor: currentCGColor) ?? .clear
  }
}

#endif

// MARK: - iOS

#if os(iOS)

typealias OSColor = UIColor

extension OSColor {
  func resolvedOSColor(colorScheme: ColorScheme? = nil) -> OSColor {
    let traitCollection: UITraitCollection? = {
      guard let colorScheme else {
        return nil
      }
      return UITraitCollection(userInterfaceStyle: colorScheme == .dark ? .dark : .light)
    }()

    return resolvedColor(with: traitCollection ?? UITraitCollection.current)
  }
}

#endif