State handler...

state_handler.rb

module StateHandlers
  class Base
    class_attribute :registered_states
    class_attribute :registered_events

    extended do
      registered_states = {}
      registered_events = Hash.new { |hash, key| hash[key] = { before: [], after: [] } }
    end

    def initialize(machine, attribute:)
      @machine = machine
      @state_attribute = attribute
    end

    def state
      registered_states[state_key].new(@machine)
    end

    def method_missing(method_name)
      registered_events[method_name][:before].each { |event| event.call(method_name, @machine) }
      state.public_send(method_name)
      registered_events[method_name][:after].each { |event| event.call(method_name, @machine) }
    end

    def self.register_state(klass)
      registered_states[klass.key] = klass
    end

    def self.register_event(event, hook = :after, callable, &block)
      registered_events[event][hook] << callable || block
    end

    private
      def state_key
        @machine.public_send(@state_attribute)
      end
  end
end