Luhn Refactor

luhn_refactor.rb

module Luhn
  def self.is_valid?(number)
    result = Luhn.card_number_to_integer_array_from_string(number)
    result = Luhn.reverse_to_start_from_right(result)
    result = Luhn.double_every_second_digit(result)
    result = Luhn.subtract_9_from_values_over_10(result)
    sum = Luhn.sum_all_digits_of_array(result)
    Luhn.luhn_is_valid?(sum)
  end

  def self.reverse_to_start_from_right(number_array)
    number_array.reverse
  end

  def self.sum_all_digits_of_array(number_array)
    number_array.inject(:+)
  end

  def self.card_number_to_integer_array_from_string(number_as_string)
    number_as_string.to_s.chars.map(&:to_i)
  end

  def self.double_every_second_digit(number_array)
    result = []
    number_array.each_with_index do |value, index|
      if is_even?(index)
        result << value
      else
        result << value * 2
      end
    end
    result
  end

  def self.subtract_9_from_values_over_10(number_array)
    number_array.map do |number|
      if number >= 10
        number - 9
      else
        number
      end
    end
  end

  def self.luhn_is_valid?(sum_total)
    (sum_total % 10 == 0)
  end

  def self.is_even?(number)
    number % 2 == 0
  end
end