In my Ruby on Rails app I have this model:

class Car < ApplicationRecord

  attr_accessor :name, :brand, :origin_country

  module ShippingCostCalculatorForJapan

    def calculate
      # Details left out for brevity
    end

    # A bunch of other expensive methods

 end

 module ShippingCostCalculatorForGermany

   def calculate
     # Details left out for brevity
   end

   # A bunch of other expensive methods

 end

end

How can I make it that only the relevant module gets loaded?

For example if I have a car object with origin_country “Japan”, only the module ShippingCostCalculatorForJapan should be applied.

How can this be done or what might be a better (= best practice) design pattern to achieve this?

As it stands now, I have a bunch of different CostCalculator modules all containing the exact same methods but with different values in them. The values are hardcoded to the respective country and can’t be changed.

I could also easily re-organize those modules into classes. What would be the best approach here?