ImageScalerCoreGraphics.swift

import CoreGraphics

struct ImageScaler {
    static func scaleToFill(_ image: CGImage, from fromRect: CGRect = .zero, in targetSize: CGSize) -> CGImage? {
        let imageSize = CGSize(width: image.width, height: image.height)
        let rect = fromRect.isEmpty ? CGRect(origin: .zero, size: imageSize) : fromRect
        let scaledRect = rect.scaled(toFillSize: targetSize)
        return scale(image, fromRect: scaledRect, in: targetSize)
    }
    
    private static func scale(_ image: CGImage, fromRect: CGRect = .zero, in targetSize: CGSize) -> CGImage? {
        let makeCroppedCGImage: (CGImage) -> CGImage? = { cgImage in
            guard !fromRect.isEmpty else { return cgImage }
            return cgImage.cropping(to: fromRect)
        }
        guard let croppedImage = makeCroppedCGImage(image) else { return nil }
        let context = CGContext(data: nil,
                                width: Int(targetSize.width),
                                height: Int(targetSize.height),
                                bitsPerComponent: croppedImage.bitsPerComponent,
                                bytesPerRow: croppedImage.bytesPerRow,
                                space: croppedImage.colorSpace ?? CGColorSpace(name: CGColorSpace.sRGB)!,
                                bitmapInfo: croppedImage.bitmapInfo.rawValue)
        context?.interpolationQuality = .high
        context?.draw(croppedImage, in: CGRect(origin: .zero, size: targetSize))
        return context?.makeImage()
    }
}