A module for the definition of lookup lists

lookups.rb

require "active_support/inflector"

module Lookups

  # Allows the definition of lookup values
  def define_lookup(const_name, lookup_codes)

    mod = Module.new do
      extend self

      @codes = lookup_codes

      def codes
        @codes
      end

      # Allow access using LookupName.code(:the_code)
      def code(code)
        send(code.to_s)
      end

      # Get the translation for the code
      def human_name(code)
        class_names = name.gsub('::','.').underscore
        I18n.t("lookups.#{class_names}.#{code}")
      end

      # All of the types for use in a form select list
      def select_list
        @codes.map { |code| [human_name(code), code] }
      end
      
      # Check that the given type exists
      def valid_type?(code)
        @codes.include?(code.to_s)
      end

      # Allow the use of LookupName.lookup_code (for example)
      def method_missing(method, *args, &block)
        return method.to_s if valid_type?(method)
        super
      end

      # Always have a respond_to with a method missing!
      def respond_to?(method)
        return true if valid_type?(method)
        super
      end

    end

    # Assign the module to its name
    const_set(const_name, mod)
  end

end

# Example

I18n.backend.store_translations('en', { lookups: { stall: { fruits: { apple: "Apple", orange: "Orange" } } } })

class Stall
  extend Lookups
  define_lookup "Fruits", %w(apple orange)
end

# Test

require "test/unit"

class TestLookups < Test::Unit::TestCase

  def test_lookup
    assert_equal("apple", Stall::Fruits.apple)
  end

  def test_lookup_by_code
    assert_equal("apple", Stall::Fruits.code(:apple))
  end

  def test_human_name
    assert_equal("Apple", Stall::Fruits.human_name(:apple))
  end

  def test_select_list
    list = [["Apple", "apple"], ["Orange", "orange"]]
    assert_equal(list, Stall::Fruits.select_list)
  end

end

# In forms it can be used in select lists like this:
#   <%= f.select :fruits, Stall::Fruits.select_list %>