class Character
  attr_accessor :strength, :level, :agility
  def initialize(level, strength, agility)
    @level, @strength, @agility = level, strength, agility
    @stat_boosts = {}
  end

  def attack_power
    stat_boost :attack_power
  end

  def stat_boost(stat)
    @stat_boosts[stat] || 0
  end

  def add_stat_boost(stat, amount)
    @stat_boosts[stat] = amount
  end

  def remove_stat_boost(stat)
    @stat_boosts.delete(stat)
  end
end

class Rogue < Character
  def attack_power
    strength + agility + (level * 2) - 20 + super
  end
end

class Druid < Character
  VALID_FORMS = [:bear, :cat, :moonkin]
  def attack_power
    super + case form
    when :bear
      (strength * 2) + (level * 3) - 20
    when :cat
      (strength * 2) + agility + (level * 2) - 20
    when :moonkin
      (strength * 2) + (level * 1.5) - 20
    end
  end

  def form=(form)
    @form = VALID_FORMS.find {|f| f == (form) } || raise("no such form")
  end
  attr_reader :form
end

progue = Rogue.new(120, 700, 70)
progue.add_stat_boost :attack_power, 200
puts progue.attack_power
# => 1190
progue.remove_stat_boost :attack_power
puts progue.attack_power
# => 990


durid = Druid.new(200, 600, 70)
durid.form = :cat
puts durid.attack_power
# => 1650