UIImage fix orientation ( rotate pixel rather than relying on exif ) -- Swift 4, no force unwraps

UIImage+Orientation.swift

import UIKit

extension UIImage {
    func fixOrientation() -> UIImage {
        
        guard let cg = cgImage, let cg_colorspace = cg.colorSpace else {
            print("Error while fixing image orientation")
            return self
        }
        
        // No-op if the orientation is already correct
        if self.imageOrientation == .up {
            return UIImage(cgImage: cg, scale: scale, orientation: imageOrientation)
        }
        
        // We need to calculate the proper transformation to make the image upright.
        // We do it in 2 steps: Rotate if Left/Right/Down, and then flip if Mirrored.
        var transform: CGAffineTransform = CGAffineTransform.identity
        
        if imageOrientation == .down || imageOrientation == .downMirrored {
            transform = transform.translatedBy(x: self.size.width, y: self.size.height)
            transform = transform.rotated(by: CGFloat(Double.pi))
        }
        
        if imageOrientation == .left || imageOrientation == .leftMirrored {
            transform = transform.translatedBy(x: self.size.width, y: 0)
            transform = transform.rotated(by: CGFloat(Double.pi / 2))
        }
        
        if imageOrientation == .right || imageOrientation == .rightMirrored {
            transform = transform.translatedBy(x: 0, y: self.size.height)
            transform = transform.rotated(by: CGFloat(-Double.pi / 2))
        }
        
        if imageOrientation == .upMirrored || imageOrientation == .downMirrored {
            transform = transform.translatedBy(x: self.size.width, y: 0)
            transform = transform.scaledBy(x: -1, y: 1)
        }
        
        if imageOrientation == .leftMirrored || imageOrientation == .rightMirrored {
            transform = transform.translatedBy(x: self.size.height, y: 0)
            transform = transform.scaledBy(x: -1, y: 1)
        }
        
        // Now we draw the underlying CGImage into a new context, applying the transform
        // calculated above.
        guard let ctx = CGContext(data: nil, width: Int(self.size.width), height: Int(self.size.height), bitsPerComponent: cg.bitsPerComponent, bytesPerRow: 0, space: cg_colorspace, bitmapInfo: cg.bitmapInfo.rawValue) else {
            print("Error while fixing image orientation")
            return self
        }
        
        ctx.concatenate(transform)
        
        if imageOrientation == .left ||
           imageOrientation == .leftMirrored ||
           imageOrientation == .right ||
           imageOrientation == .rightMirrored {
            ctx.draw(cg, in: CGRect(x: 0, y: 0, width: self.size.height, height: self.size.width))
        }
        else {
            ctx.draw(cg, in: CGRect(x: 0, y: 0, width: self.size.width, height: self.size.height))
        }
        
        // And now we just create a new UIImage from the drawing context and return it
        guard let res = ctx.makeImage() else {
            print("Error while fixing image orientation")
            return self
        }
        return UIImage(cgImage: res)
    }
}