has_provider_subclass.rb

module HasProviderSubclass
  USERS = []

  module ClassMethods
    def type_to_class_string type
      @type_to_class_string ||= Hash.new do |h, type|
        h[type] = "#{self.to_s}::#{type.classify}"
      end
      @type_to_class_string[type]
    end

    def type_to_class type
      @type_to_class ||= Hash.new do |h, cs|
        h[cs] = type_to_class_string(cs).constantize
      end
      @type_to_class[type]
    end
    # alias call type_to_class
  end

  module InstanceMethods
    def type
      self.class.to_s.demodulize.underscore
    end
  end

  def self.included(receiver)
    USERS << receiver
    receiver.extend         ClassMethods
    receiver.send :include, InstanceMethods

    # Makes Klass('type') a method
    tree = receiver.to_s.split("::")
    klass = tree.pop

    if tree.empty?
      Kernel.module_eval do
        define_method klass do |type|
          receiver.type_to_class(type)
        end
      end
    else
      namespace = tree.join("::").constantize
      puts "Defining method #{klass} on namespace #{namespace}"
      namespace.module_eval do
        define_singleton_method klass do |type|
          receiver.type_to_class(type)
        end
      end
    end
  end
end