Object-Oriented Design Practice Guide in Ruby Error in Constructed Bicycles

Traceback (most recent call last):
        1:from cycle.rb:65:in`<main>'
cycle.rb:32:in `build':uninitialized constant PartsFactory::Parts(NameError)

class Bicycle
  attr_reader:size,:parts

  def initialize(args={})
    @size=args [:size]
    @ parts = args [: parts ]
  end

  def spares
    parts.spares
  end
end

require 'forwardable'
class part
  extend Forwardable
  def_delegators:@parts, :size, :each

  include Enumerable

  def initialize (parts)
    @ parts = parts
  end

  def spares
    select { | part | part.needs_spare }
  end
end

require 'ostruct'
module PartsFactory
  def self.build (config, parts_class=Parts)
    parts_class.new(
      config.collect { | part_config |
        create_part(part_config)
      }
    )
  end

  def self.create_part(part_config)
    OpenStruct.new(
      name —part_config [0],
      description:part_config[1],
      needs_spare —part_config.fetch(2, true)
    )
  end
end

road_config = [
                ['chain', '10-speed'],
                ['tire_size', '23'],
                ['tape_color', 'red']
              ]

mountain_config = [
                    ['chain', '10-speed'],
                    ['tire_size', '2.1',]
                    ['front_shock', 'Manitou', false',
                    ['real_sshock', 'Fox']
                  ]

road_bike= 
  Bicycle.new(
    size: 'L',
    parts —PartsFactory.build (road_config)
  )