swift-rewrite-redux.swift

extension CGSize {
    func scaled(byFactor factor: CGFloat) -> CGSize {
        return CGSize(width: width * factor,
                      height: height * factor)
    }
}

extension CGSize {
    func scaled(toSize: CGSize, mode: UIImage.ScaleMode) -> CGSize {
        let (widthFactor, heightFactor) = (toSize.width / width, toSize.height / height)
        
        let scaleFactor: CGFloat
        
        switch mode {
        case .aspectFit:
            scaleFactor = min(widthFactor, heightFactor)
        case .aspectFill:
            scaleFactor = max(widthFactor, heightFactor)
        }
        
        return scaled(byFactor: scaleFactor)
    }
}

extension CGRect {
    struct Anchor {
        let vertical: Vertical
        let horizontal: Horizontal
        
        
        enum Horizontal {
            case left
            case center
            case right
        }
        
        enum Vertical {
            case top
            case center
            case bottom
        }
    }

    // Initializes a CGRect with an origin such that it is "anchored"
    // inside a rect with size `containerSize`
    init(size: CGSize, anchor: Anchor, containerSize: CGSize) {
        let originX: CGFloat
        let originY: CGFloat
        
        switch anchor.vertical {
        case .top:
            originY = 0
        case .center:
            originY = (containerSize.height - size.height) / 2
        case .bottom:
            originY = containerSize.height - size.height
        }
        
        switch anchor.horizontal {
        case .left:
            originX = 0
        case .center:
            originX = (containerSize.width - size.width) / 2
        case .right:
            originX = containerSize.width - size.width
        }
        
        self.origin = CGPoint(x: originX, y: originY)
        self.size = size
    }
}

extension UIImage {
    enum ScaleMode {
        case aspectFit
        case aspectFill
    }
    
    func cropped(
        toSize: CGSize,
        croppingAnchor: CGRect.Anchor = CGRect.Anchor(vertical: .center, horizontal: .center)
        ) -> UIImage {
        
        let requiresResizing = !size.equalTo(toSize)
        guard requiresResizing else {
            return self
        }
        
        let drawingRect = CGRect(size: size, anchor: croppingAnchor, containerSize: toSize)
        
        let scaledImage: UIImage
        
        UIGraphicsBeginImageContextWithOptions(toSize, false, 0.0)
        draw(in: drawingRect)
        scaledImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        
        return scaledImage
    }
    
    func scaled(
        toSize: CGSize,
        mode: ScaleMode,
        croppingAnchor: CGRect.Anchor = CGRect.Anchor(vertical: .center, horizontal: .center)
        ) -> UIImage {
        
        let requiresResizing = !size.equalTo(toSize)
        guard requiresResizing else {
            return self
        }
        
        let drawingSize = size.scaled(toSize: toSize, mode: mode)
        let drawingRect = CGRect(size: drawingSize, anchor: croppingAnchor, containerSize: toSize)
        
        let scaledImage: UIImage
        
        UIGraphicsBeginImageContextWithOptions(toSize, false, 0.0)
        draw(in: drawingRect)
        scaledImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        
        return scaledImage
    }
}