Rubs refactoring

gistfile1.rb

class TrafficLight
  
  def initialize
    @state = lights.first
  end
 
  def change_to(change)
    light = lights.find{|l| l.color == change.to_sym }
    raise ArgumentError, "Invalid traffic light: #{change}" unless light

    @state = light
  end
 
  def signal
    @state.signal
  end
  
  def next_state
    @state.next
  end

  private

  def lights
    @lights ||= [
      Proceed.new,
      Caution.new,
      Stop.new
    ]
  end

  class Light
    NEXT = {
      :green  => 'caution',
      :yellow => 'stop',
      :red    => 'proceed'
    }

    attr_reader :color

    def initialize
      raise NotImplementedError
    end

    def signal
      puts "Turning on #{color} lamp"
    end

    def next
      NEXT[color]
    end
  end

  class Proceed < Light
    def initialize
      @color = :green
    end
  end

  class Caution < Light
    def initialize
      @color = :yellow
    end

    def signal
      super
      puts "Ring ring ring!"
    end
  end

  class Stop < Light
    def initialize
      @color = :red
    end
  end
end

t = TrafficLight.new

[
  :yellow,
  :red,
  :green
].each do |state|
  t.signal
  t.next_state
  t.change_to(state)
end

t.change_to(:green)
t.change_to("yellow")
t.change_to("purple")