The Gilded Rose Code Kata - a 'solution'

update.rb

def update_quality(items)  
  rules = { "Conjured"  => { ds:-1, mq:50, dq:[ -4, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2 ]},
            "Sulfuras"  => { ds: 0, mq:80, dq:[  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0 ]},
            "Aged Brie" => { ds:-1, mq:50, dq:[ +2, +1, +1, +1, +1, +1, +1, +1, +1, +1, +1, +1 ]},
            "Backstage" => { ds:-1, mq:50, dq:[-50, +3, +3, +3, +3, +3, +2, +2, +2, +2, +2, +1 ]},
            "."         => { ds:-1, mq:50, dq:[ -2, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1 ]}}
  items.each do |item|
    rules.each do |key,rule|
      if item.name=~/#{key}/
        item.quality += rule[:dq][ [0, item.sell_in, 11].sort[1] ]
        item.quality = [0, item.quality, rule[:mq]].sort[1]
        item.sell_in += rule[:ds]
        break
      end  
    end  
  end
end