runtimerevolution/citizenship

module Citizenship
  #http://www.cartaodecidadao.pt/images/stories/Algoritmo_Num_Documento_CC.pdf
  def self.valid_citizen_card!(number)
    id_number = remove_special_chars(number)

    raise CitizenCardError, :size if id_number.size != 12

    double_digit = false
    conversion_table = ('a'..'z').to_a
    check_digit = id_number.reverse.split('').map do |element|
      #switch letters for the value in the conversion table (see 2.3. on Algoritmo_Num_Documento_CC.pdf)
      is_number?(element) ? element : conversion_table.find_index(element.downcase) + 10
    end.map(&:to_i).map do |digit|
      begin
        if double_digit #starting on the 2nd value double every value steping by 2
          value = digit * 2
          value >= 10 ? value - 9 : value #If the doubling result is 10 or more, subtract 9
        else
          digit
        end
      ensure
        double_digit = not(double_digit)
      end
    end.reduce(:+) #sum everything

    raise CitizenCardError, :invalid_check_digit if check_digit % 10 != 0
    number
  end

  def self.valid_citizen_card?(number)
    valid_citizen_card!(number)
    true
  rescue CitizenCardError
    false
  end
end