Finnish numbers generator

finnish_numbers.rb

#encoding: utf-8
module Modules
  module FinnishNumbers
    def self.convert_to_s(number)
      number = number.to_i
      return "nolla" if number.zero?
      number_symbols = number.to_s.split('').map { |digit| digit.to_i }
      digits = "", "yksi", "kaksi", "kolme", "neljä", "viisi", "kuusi", "seitsemän", "kahdeksan", "yhdeksän", "kymmenen"
      if number <= 10
        digits[number_symbols[0]]
      elsif number < 20
        digits[number_symbols[1]] + "toista"
      elsif number < 100
        digits[number_symbols[0]] + "kymmenta" + self.convert_to_s(number.to_s[-1, 1])
      elsif number < 200
        "sata" + self.convert_to_s(number.to_s[-2, 2])
      elsif number < 1000
        digits[number_symbols[0]] + "sataa" + self.convert_to_s(number.to_s[-2, 2])
      elsif number < 2000
        "tuhat" + self.convert_to_s(number.to_s[-3, 3])
      elsif number < 10000
        digits[number_symbols[0]] + "tuhatta" + self.convert_to_s(number.to_s[-3, 3])
      elsif number == 10000
        digits[10] + "tuhatta"
      end
    end
  end
end