fits.m

- (CGSize)sizeThatFits:(CGSize)size {
    CGSize imageSize = self.imageView.image.size;
    
    if (CGSizeEqualToSize(imageSize, CGSizeZero)) {
        return CGSizeZero;
    }
    
    if (imageSize.width <= size.width && imageSize.height <= size.height)
        return imageSize;
    
    CGFloat deltaWidth = size.width - imageSize.width;
    CGFloat deltaHeight = size.height - imageSize.height;
    
    CGSize resultSize;
    if (deltaWidth < deltaHeight) {
        // constrain the width
        CGFloat imageWidthToConstrainedWidthRatio = imageSize.width / size.width;
        resultSize = CGSizeMake(size.width, imageSize.height * (1 / imageWidthToConstrainedWidthRatio));
    } else {
        // constrain the height
        CGFloat imageHeightToConstrainedHeightRatio = imageSize.height / size.height;
        resultSize = CGSizeMake(imageSize.width * (1 / imageHeightToConstrainedHeightRatio), size.height);
    }
    
    return resultSize;
}