class BatteryBank
  attr_reader :batteries

  def initialize(batteries)
    @batteries = batteries
  end

  def self.for(string)
    new string.split("").map(&:to_i)
  end

  def joltage_for_batteries(num_batteries)
    num_batteries.downto(1).reduce([[], 0]) do |acc, enabled_battery_index|
      max_digit = batteries[(acc[1])..(-enabled_battery_index)].max
      max_digit_index = batteries[(acc[1])..].find_index(max_digit)
      [acc[0] + [max_digit], acc[1] + max_digit_index + 1]
    end[0].map(&:to_s).join("").to_i
  end

  def maximum_joltage
    joltage_for_batteries(2)
  end

  def override_joltage
    joltage_for_batteries(12)
  end
end