UIImage+Scaling.swift

extension UIImage {
    func scaleFactorFor(maxSize: CGSize) -> CGFloat {
        let imageSize = self.size
        guard imageSize.width > maxSize.width || imageSize.height > maxSize.height else {
            // image is already smaller than max
            return 1.0
        }
        
        let widthScaleFactor = maxSize.width / imageSize.width
        let heightScaleFactor = maxSize.height / imageSize.height
        return min(widthScaleFactor, heightScaleFactor)
    }
    
    func scaledBy(factor: CGFloat) -> UIImage? {
        guard factor != 1.0 else { return self }
        let scaledSize = CGSize(width: self.size.width * factor, height: self.size.height * factor)
        
        UIGraphicsBeginImageContextWithOptions(scaledSize, true, self.scale)
        draw(in: CGRect(origin: .zero, size: scaledSize))
        let image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return image
    }
}