Gilded Rose Ruby Solution

gilded_rose.rb

class GildedRose

  attr_reader :name, :days_remaining, :quality

  ∞ = Float::INFINITY

  CHEESE = {
    'Normal Item'                               => { -∞..0 => -2, 1..∞ => -1 },
    'Aged Brie'                                 => { -∞..0 =>  2, 1..∞ =>  1 },
    'Conjured Mana Cake'                        => { -∞..0 => -4, 1..∞ => -2 },
    'Backstage passes to a TAFKAL80ETC concert' => { -∞..0 => -∞, 1..5 =>  3, 6..10 => 2, 10..∞ => 1 }
  }

  def initialize(name:, days_remaining:, quality:)
    @name           = name
    @days_remaining = days_remaining
    @quality        = quality
  end

  def tick
    return if name  == 'Sulfuras, Hand of Ragnaros'
    @quality        += CHEESE[name].select { |range| range === days_remaining }.values.first
    @quality         = quality.clamp(0, 50)
    @days_remaining -= 1
  end

end