Create an image thumbnail with an aspect fill resize mode

UIImage+Resize.swift

extension UIImage {
  enum AspectOrientation {
    case portrait
    case square
    case landscape
  }
  
  var aspectRatio: CGFloat {
    return size.aspectRatio
  }
  
  var aspectOrientation: AspectOrientation {
    if aspectRatio > 1 {
      return .landscape
    } else if aspectRatio < 1 {
      return .portrait
    } else {
      return .square
    }
  }
  
  func resizeAspectFill(to destinationSize: CGSize) -> UIImage {
    let canvas = CGRect(origin: .zero, size: destinationSize)

    return UIGraphicsImageRenderer(bounds: canvas).image { _ in
      let transform: CGAffineTransform

      switch aspectOrientation {
      case .portrait:
        let scale = destinationSize.width / size.width
        let height = size.height * scale
        let translation = CGAffineTransform(translationX: 0, y: (destinationSize.height - height) / 2)
        transform = CGAffineTransform(scaleX: scale, y: scale).concatenating(translation)

      case .landscape:
        let scale = destinationSize.height / size.height
        let width = size.width * scale
        let translation = CGAffineTransform(translationX: (destinationSize.width - width) / 2, y: 0)
        transform = CGAffineTransform(scaleX: scale, y: scale).concatenating(translation)

      case .square:
        let scale = destinationSize.width / size.width
        transform = CGAffineTransform(scaleX: scale, y: scale)
      }

      let aspectFillBounds = CGRect(origin: .zero, size: size).applying(transform)
      draw(in: aspectFillBounds)
    }
  }
}