gilded_rose_refactored.rb

class GildedRose

  def initialize(items)
    @items = items
  end

  def update_quality()
    @items.each do |item|
      ItemMapper.update(item)
    end
  end
end

class Item
  attr_accessor :name, :sell_in, :quality

  def initialize(name, sell_in, quality)
    @name = name
    @sell_in = sell_in
    @quality = quality
  end

  def to_s()
    "#{@name}, #{@sell_in}, #{@quality}"
  end
end

class BaseItemHandler
  attr_reader :item

  def initialize(item)
    @item = item
  end

  def update
    update_quality
    update_sell_in
  end

  private

  def update_quality
  end

  def update_sell_in
  end
end

class DefaultItemHandler < BaseItemHandler
  private

  def update_quality
    if item.sell_in > 0
      quality = item.quality - 1
    else
      quality = item.quality - 2
    end

    item.quality = quality if quality >= 0
  end

  def update_sell_in
    item.sell_in -= 1
  end
end

class ConjuredManaCakeHandler < BaseItemHandler
  private

  def update_quality
    quality = item.quality - 2
    item.quality = quality if quality >= 0
  end

  def update_sell_in
    item.sell_in -= 1
  end
end

class BackstagePassesHandler < BaseItemHandler
  private

  def update_quality
    quality = if item.sell_in > 10
                item.quality + 1
              elsif item.sell_in > 5
                item.quality + 2
              elsif item.sell_in > 0
                item.quality + 3
              else
                0
              end

    item.quality = quality if quality <= 50
    item.quality = 50 if quality > 50
  end

  def update_sell_in
    item.sell_in -= 1
  end
end

class SulfurasHandler < BaseItemHandler
end

class AgedBrieHandler < BaseItemHandler
  private

  def update_quality
    if item.sell_in > 0
      quality = item.quality + 1
    else
      quality = item.quality + 2
    end

    item.quality = quality if quality <= 50
  end

  def update_sell_in
    item.sell_in -= 1
  end
end

class ItemMapper
  attr_reader :item

  MAP = {
    'Aged Brie'                                 => AgedBrieHandler,
    'Sulfuras, Hand of Ragnaros'                => SulfurasHandler,
    'Backstage passes to a TAFKAL80ETC concert' => BackstagePassesHandler,
    'Conjured Mana Cake'                        => ConjuredManaCakeHandler,
  }

  def initialize(item)
    @item = item
  end

  def update
    handler.new(item).update
  end

  def self.update(item)
    new(item).update
  end

  private

  def handler
    @handler ||= MAP[item.name] || DefaultItemHandler
  end
end