8_30.rb

class Bicycle
  attr_reader :size, :parts

  def initialize(size:, parts:)
    @size       = size
    @parts      = parts
  end

  def spares
    parts.spares
  end
end

require 'forwardable'
class Parts
  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',        '11-speed'],
   ['tire_size',    '23'],
   ['tape_color',   'red']]

mountain_config =
  [['chain',        '11-speed'],
   ['tire_size',    '2.1'],
   ['front_shock',  'Manitou'],
   ['rear_shock',   'Fox', false]]

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

puts road_bike.spares.class
# => Array

puts road_bike.spares
# => #<OpenStruct name="chain", description="11-speed", needs_spare=true>
# => #<OpenStruct name="tire_size", description="23", needs_spare=true>
# => #<OpenStruct name="tape_color", description="red", needs_spare=true>


mountain_bike =
  Bicycle.new(
    size: 'L',
    parts: PartsFactory.build(config: mountain_config))

puts mountain_bike.spares.class
# => Array

puts mountain_bike.spares
# => #<OpenStruct name="chain", description="11-speed", needs_spare=true>
# => #<OpenStruct name="tire_size", description="2.1", needs_spare=true>
# => #<OpenStruct name="front_shock", description="Manitou", needs_spare=true>


################
recumbent_config =
  [['chain',        '9-speed'],
   ['tire_size',    '28'],
   ['flag',         'tall and orange']]

recumbent_bike =
  Bicycle.new(
    size: 'L',
    parts: PartsFactory.build(config: recumbent_config))

puts recumbent_bike.spares
# => #<OpenStruct name="chain", description="9-speed", needs_spare=true>
# => #<OpenStruct name="tire_size", description="28", needs_spare=true>
# => #<OpenStruct name="flag", description="tall and orange", needs_spare=true>