module Kangaru::Concern

def append_features(base)
  super
  evaluate_concern_blocks!(base)
end

def class_methods(&)
  if const_defined?(:ClassMethods)
    const_get(:ClassMethods)
  else
    const_set(:ClassMethods, Module.new)
  end.module_eval(&)
end

def evaluate_concern_blocks!(base)
  base.extend(const_get(:ClassMethods)) if const_defined?(:ClassMethods)
  base.class_eval(&@included) if instance_variable_defined?(:@included)
end

def included(base = nil, &block)
  super base if base
  return if block.nil?
  @included = block
end