Scale and fit an image in a size

ScaleAndFit.swift

extension UIImage {
    /// Aspect fit an image from a size. (center)
    ///
    /// The input size is the minimum size of the output image. The size of `self` is the
    /// maximum size of the output image. Aspect ratio is maintained. Transparency is added to the
    /// sides of the output image to keep the image centered.
    ///
    /// - parameter in: The `CGSize` in which to scale and center `self`.
    func scaleAndFit(in inputSize: CGSize) -> UIImage? {
        // Scale rect to fit image, if image is larger.
        // E.g. image 6000x4000, rect 200x400, results in 6000 x 12000
        let scaledSize: CGSize = {
            let ratio = (size.height > size.width) ?
                max(size.height / inputSize.height, 1.0):
                max(size.width / inputSize.width, 1.0)
            return CGSize(width: inputSize.width*ratio, height: inputSize.height*ratio)
        }()

        // Fit image inside scaled rect
        // E.g. image 6000x4000, scaled rect 6000x12000, results in (0, 4000, 6000, 4000)
        let scaledAspectFitRect = AVMakeRect(aspectRatio: size, insideRect: CGRect(origin: .zero, size: scaledSize))

        // Create the image
        UIGraphicsBeginImageContextWithOptions(scaledSize, false, 0.0)
        draw(in: scaledAspectFitRect)
        let image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()

        return image
    }
}