scalecrop.swift

import UIKit

// Swift rewrite challenge
// Starting point: https://gist.github.com/jkereako/200342b66b5416fd715a#file-scale-and-crop-image-swift

func scaleAndCropImage(
    image: UIImage,
    toSize size: CGSize,
    fitImage: Bool = true
    ) -> UIImage {
    
    // Return original when cropping is not needed
    guard !CGSizeEqualToSize(image.size, size) else { return image }
    
    // Calculate scale factor for fit or fill
    let (widthFactor, heightFactor) = (size.width / image.size.width, size.height / image.size.height)
    let fitFillTest = fitImage ? widthFactor < heightFactor : widthFactor > heightFactor
    let scaleFactor = fitFillTest ? widthFactor : heightFactor
    
    // Establish drawing destination, which may start outside the drawing context bounds
    let (scaledWidth, scaledHeight) = (image.size.width * scaleFactor, image.size.height * scaleFactor)
    let drawingOrigin = CGPoint(
        x: (size.width - scaledWidth) / 2.0,
        y: (size.height - scaledHeight) / 2.0)
    
    // Perform drawing and return image
    UIGraphicsBeginImageContextWithOptions(size, false, 0.0)
    let scaledImage: UIImage
    do {
        // Fill background
        UIColor.blackColor().setFill(); UIRectFill(CGRect(origin: .zero, size: size))
        
        // Draw scaled image
        let drawingRect: CGRect = CGRect(
            origin: drawingOrigin,
            size: CGSize(width: scaledWidth, height: scaledHeight))
        image.drawInRect(drawingRect)
        
        // Fetch image
        scaledImage = UIGraphicsGetImageFromCurrentImageContext()!
    }
    UIGraphicsEndImageContext()
    return scaledImage
}

// Test with some basic placeholder data
guard let url = NSURL(string: "http://placehold.it/300x150") else { fatalError("Bad URL") }
guard let data = NSData(contentsOfURL: url) else { fatalError("Bad data") }
guard let img = UIImage(data: data) else { fatalError("Bad data") }

let outImageFit = scaleAndCropImage(img, toSize: CGSize(width: 200, height: 200))
let outImageFill = scaleAndCropImage(img, toSize: CGSize(width: 200, height: 200), fitImage: false)

@PaulTaykalo

In my real world code, I use code that passes a context. You can always get context from a valid drawing session and UIKit supports a context stack, so you can push the context, perform drawing, and then pull an image to return and pop the context.