Calculatable attributes concern for ActiveRecord models

calculatable_attributes.rb

module CalculatableAttributes
  extend ActiveSupport::Concern

  class_methods do
    def calculate(attribute, &block)
      attr_name = attribute.to_s.delete("?")
      attr_block = block

      @@calculate_methods ||= {}
      @@calculate_methods[name] ||= {}
      @@calculate_methods[name][attr_name] = attr_block

      define_method(:"calculate_#{attr_name}") do
        instance_exec(&attr_block)
      end

      define_method(:"calculate_#{attr_name}!") do
        assign_attributes(attr_name => method(:"calculate_#{attr_name}").call)
      end

      define_method(attribute) do
        attributes[attr_name] || method(:"calculate_#{attr_name}").call
      end

      unless method_defined?(:calculate_all!)
        define_method(:calculate_all!) do
          @@calculate_methods[name].each do |attr_name, attr_block|
            method(:"calculate_#{attr_name}!").call
          end
        end
      end
    end
  end
end