allergy.rb

class Allergy
  attr_reader :score
  @@allergies = {
    eggs: 1,
    peanuts: 2,
    shellfish: 4,
    strawberries: 8,
    tomatoes: 16,
    chocolate: 32,
    pollen: 64,
    cats: 128
  }.to_a.reverse.to_h

  def initialize(name, score)
    validate(score) 
    @name = name.capitalize
    @score = score
    @list = get_allergies
  end 

  def validate(score)
    if score > 255 || score < 1
      raise StandardError, "Wrong score. Enter a number between 1 and 255"
    end 
  end 

  def get_allergies 
    allergic_to = []
    temp = @score
    @@allergies.each do |key, value|
      if temp >= value
        allergic_to << key
        temp -= value
      end 
    end 
    return allergic_to
  end 

  def list_print_pretty
    items = @list.map.with_index do |item, index|
      if index == @list.length - 1
        " and #{item}"
      elsif index == @list.length - 2
        item
      else
        "#{item}, "
      end 
    end 
    return items.join("")
  end 

  def list 
    "#{@name} is allergic to #{list_print_pretty}"
  end 

  def allergic_to_item?(item)
    @list.include?(item.to_sym)
  end 
end

app.rb

require_relative 'allergy'

tom = Allergy.new("tom", 255)
p tom.allergic_to_item?("chocolate")
p tom.list
p tom.score