Simple State Machine for an ActiveRecord model (see "after_initialize")

state_machine.rb

module StateMachine
  # assumption: just using "state" as our column.  easy enough to change

  def self.included(mod)
    mod.extend ClassMethods
    super
  end

  module ClassMethods
    def initial_state(state)
      state(state)
      self.class_eval do
        define_method(:after_initialize) do
          self.state ||= state.to_s
        end
      end
    end

    def state(state)
      @@states ||= []
      @@states << state
      self.class_eval do
        define_method("#{state}?".to_sym) do
          state == self.state.to_sym
        end
      end
    end

    def event(event, transitions)
      @@events ||= {}
      @@events[event] = transitions
      self.class_eval do
        define_method("#{event}!") do
          current_state = state.to_sym
          transition = @@events[event].select { |old, new| old == current_state }.last
          self.update_attribute(:state, transition.last.to_s) if transition && @@states.include?(transition.last)
          self
        end
      end
    end
  end

end