monsters.rb

require 'yaml'

class Monster
  def self.bestiary
    @bestiary ||= YAML.load_file("monsters.yml")
  end

  def self.random
    new bestiary.keys.sample
  end

  attr_accessor :name,
                :attack_text,
                :max_hit_points,
                :strength,
                :speed,
                :health

  def initialize(name)
    attributes = Monster.bestiary.fetch(name) {
      raise ArgumentError.new("Name must be one of #{Monster.bestiary.keys.join(", ")}.")
    }

    attributes.each do |attribute, value|
      public_send("#{attribute}=", value)
    end
    self.name = name
    self.health = max_hit_points
  end
end