image_resizer.rb

def image_resizer max, height, width
  # capture any nil or 0/less-than-0 objects and set them to the max value, since they need a value.
  # Assume max size is desired unless we're told otherwise.
  height = height.nil? || height <= 0 ? max : height
  width = width.nil? || width <= 0 ? max : width
  
  # Find out if any of the dimensions are bigger than the max size
  if height > max || width > max
    # isolate the largest dimension -> it doesn't really matter which one we look at, as long as it's the largest
    largest_dimension = height > max ? height : width
    # find the difference between the two and isolate that, convert to floats so we don't divide by zero
    difference = largest_dimension.to_f / max.to_f
    
    # divide the dimensions by that difference and reset the height and width variables.  Then convert back to ints and round down
    height = (height.to_f / difference).to_i
    width = (width.to_f / difference).to_i
  end

  # this outputs it in a manner that's consistent with use in an image_tag
  "#{width}x#{height}"
end