Hearthstone packs needed to complete collection

TOTAL_CARDS = { :common => 100, :rare => 70, :epic => 50, :legendary => 30 }
RARITY_CHANCE = { :legendary => 0.005, :epic => 0.025, :rare => 0.1, :common => 1 }
DISENCHANTED_ARCANE_DUST = { :common => 2, :rare => 10, :epic => 100, :legendary => 400 }
CRAFT_ARCANE_DUST = { :legendary => 1600, :epic => 400, :rare => 100, :common => 10 }
CARDS_PER_PACK = 5

class Card
  attr_accessor :rarity, :number
  def initialize(rarity, number)
    @rarity = rarity
    @number = number
  end
end

class PackGenerator

  def initialize
    @collection = { :common => [], :rare => [], :epic => [], :legendary => [] }
    @arcane_dust = 0
    @packs_open = 0
    @disenchanted = 0
  end

  def check_packs_needed
    while !is_collection_complete?
      add_collection(random_pack)
      @packs_open += 1
      #puts info
    end

    return @packs_open
  end

  def add_collection(pack)
    pack.each do |card|
      unless @collection[card.rarity].any? { |c| c.number == card.number }
        @collection[card.rarity] << card
      else
        disenchant_card(card)
      end
    end
  end

  def disenchant_card(card)
    @arcane_dust += DISENCHANTED_ARCANE_DUST[card.rarity]
    @disenchanted += 1

    CRAFT_ARCANE_DUST.each do |rarity, craft_cost|
      if @collection[rarity].size != TOTAL_CARDS[rarity]
        craft_card(rarity) if craft_cost <= @arcane_dust
        break
      end
    end
  end

  def craft_card(rarity)
    (1..TOTAL_CARDS[rarity]).each do |i|
      unless @collection[rarity].any? { |card| card.number == i }
        @arcane_dust -= CRAFT_ARCANE_DUST[rarity]
        @collection[rarity] << Card.new(rarity, i)
        return
      end
    end
  end

  def random_pack
    pack = []
    (1..5).each do |i|
      pack << random_rarity_card(i == 5 && !pack.any? { |card| card.rarity != :common })
    end
    return pack
  end

  def random_rarity_card(force_atleast_rare)
    r = rand # get rarity
    while r < RARITY_CHANCE[:rare]
      r = rand
    end if force_atleast_rare

    card = nil
    RARITY_CHANCE.each do |rarity, chance|
      if r < chance
        card = Card.new(rarity, random_card_from_rarity(TOTAL_CARDS[rarity]))
        break
      end
    end

    return card
  end

  def random_card_from_rarity(max)
    return (rand * (max - 1) + 1).round
  end

  def is_collection_complete?
    @collection.each do |rarity, list|
      return false if list.size != TOTAL_CARDS[rarity]
    end
    return true
  end

  def info
    msg = ""
    msg << "packs: #{@packs_open}, "
    msg << "common: #{@collection[:common].size}, "
    msg << "rare: #{@collection[:rare].size}, "
    msg << "epic: #{@collection[:epic].size}, "
    msg << "leg: #{@collection[:legendary].size}, "
    msg << "dis: #{@disenchanted}, "
    msg << "dust: #{@arcane_dust}"
    msg << "."
    return msg
  end
end

results = []
(0..49).each do |i|
  p = PackGenerator.new
  results << p.check_packs_needed
  puts "Packs needed: #{results[i]}."
end
puts "Average: #{results.inject{|sum,x| sum + x} / results.size}"
puts "Max: #{results.max}"
puts "Min: #{results.min}"

#Packs needed: 1167.
#Packs needed: 1310.
#Packs needed: 1598.
#Packs needed: 1471.
#Packs needed: 1178.
#Packs needed: 1288.
#Packs needed: 1434.
#Packs needed: 1254.
#Packs needed: 1141.
#Packs needed: 1246.
#Packs needed: 1394.
#Packs needed: 1417.
#Packs needed: 1200.
#Packs needed: 1399.
#Packs needed: 1224.
#Packs needed: 1250.
#Packs needed: 1489.
#Packs needed: 1277.
#Packs needed: 1512.
#Packs needed: 1182.
#Packs needed: 1383.
#Packs needed: 1185.
#Packs needed: 1386.
#Packs needed: 1280.
#Packs needed: 1288.
#Packs needed: 1386.
#Packs needed: 1484.
#Packs needed: 1238.
#Packs needed: 1378.
#Packs needed: 1338.
#Packs needed: 1332.
#Packs needed: 1480.
#Packs needed: 1404.
#Packs needed: 1522.
#Packs needed: 1446.
#Packs needed: 1411.
#Packs needed: 1412.
#Packs needed: 1332.
#Packs needed: 1289.
#Packs needed: 1122.
#Packs needed: 1228.
#Packs needed: 1245.
#Packs needed: 1407.
#Packs needed: 1370.
#Packs needed: 1342.
#Packs needed: 1411.
#Packs needed: 1211.
#Packs needed: 1224.
#Packs needed: 1305.
#Packs needed: 1257.
#Average: 1330
#Max: 1598
#Min: 1122