gilded_rose.rb

require './item.rb'
require 'delegate'

class ItemWrapper < SimpleDelegator
  def self.wrap(item)
    case item.name
      when "Aged Brie"
        AgedBrie.new(item)
      when /Backstage passes/
        BackstagePass.new(item)
      when /Conjured/
        ConjuredItem.new(item)
      when /Sulfuras/
        LegendaryItem.new(item)
      else
        new(item)
    end
  end

  def update
    age
    update_quality
  end

  def age
    self.sell_in -= 1
  end

  def update_quality
    self.quality += quality_adjustment
  end

  def quality_adjustment
    if sell_in < 0
      past_date_adjustment
    else
      normal_adjustment
    end
  end

  def normal_adjustment
    -1
  end

  def past_date_adjustment
    2 * normal_adjustment
  end

  def quality=(new_quality)
    new_quality = 0 if new_quality < 0
    new_quality = 50 if new_quality > 50
    super(new_quality)
  end
end

class AgedBrie < ItemWrapper
  def normal_adjustment
    -super
  end
end

class BackstagePass < ItemWrapper
  def normal_adjustment
    if sell_in < 5
      3
    elsif sell_in < 10
      2
    else
      1
    end
  end

  def past_date_adjustment
    -quality
  end
end

class ConjuredItem < ItemWrapper
  def normal_adjustment
    2 * super
  end
end

class LegendaryItem < ItemWrapper
  def update
    # Nothing to do - Legendary items don't change
  end
end

class GildedRose

  @items = []

  def initialize
    @items = []
    @items << Item.new("+5 Dexterity Vest", 10, 20)
    @items << Item.new("Aged Brie", 2, 0)
    @items << Item.new("Elixir of the Mongoose", 5, 7)
    @items << Item.new("Sulfuras, Hand of Ragnaros", 0, 80)
    @items << Item.new("Backstage passes to a TAFKAL80ETC concert", 15, 20)
    @items << Item.new("Conjured Mana Cake", 3, 6)
  end

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