module DelegateAttributes

  def self.included(base)
    base.class_eval do
      extend ClassMethods
    end
  end

  module ClassMethods
    def delegate_or_override(*methods)
      options = methods.pop
      unless options.is_a?(Hash) && to = options[:to]
        raise ArgumentError, "Delegation needs a target. Supply an options hash with a :to key as the last argument (e.g. delegate_or_override :hello, :to => :greeter)."
      end

      methods.each do |method|
        method_str = ""
        source_method, dest_method = *method
        dest_method ||= source_method

        method_str =<<-END_DEF
          def #{source_method}(*args, &block)
            if read_attribute(:#{source_method})
              read_attribute(:#{source_method})
            elsif #{to}
              #{to}.__send__(#{dest_method.inspect}, *args, &block)
            end
          end
        END_DEF
        file, line = caller[0].split(/:/)
        module_eval(method_str, file, line.to_i)
      end
    end
  end
end

ActiveRecord::Base.send(:include, DelegateAttributes)