The final ImageTagOptionParser class also take account of other logic that lived in a separate controller. Thus I now have one single place that knows all the rules for the options. Plus I now have an easy way to write a test for it. (this was done TDD bt

after.rb

transformations = ImageTagOptionParser.new(options)
final_filepath = "#{prefix}/resources/images/#{file}?#{transformations}"

class ImageTagOptionParser
  KEYS = %w{scale constrain crop cropresize}
  attr_accessor :transform
  
  def initialize(options = {})
    options.reject!{|key, value| (key == "scale" && value.to_s == "100")}
    first_valid_key = KEYS.find{|key| !options[key].blank?}
    transform = options.find{|key, val| key == first_valid_key }
  end
  
  def to_s
    transform.join("=") unless blank?
  end

  def blank?
    transform.blank?
  end
end

before.rb

scale = options['scale'] ? options.delete('scale') : '100' # 100%
crop = options['crop'] or nil
cropresize = options['cropresize'] or nil
if options['constrain']
  dimensions = "&constrain=#{options.delete('constrain')}"
elsif crop
  dimensions = "&crop=#{crop}"
elsif cropresize
  dimensions = "&cropresize=#{cropresize}"
else
  dimensions = ''
end

%{<img src="#{prefix}/resources/images/#{file}?scale=#{scale}#{dimensions}"#{attributes} />}