# File lib/faker/finance.rb, line 9 def credit_card(*types) types = CREDIT_CARD_TYPES if types.empty? type = types.sample template = numerify(fetch("credit_card.#{type}")) # calculate the luhn checksum digit multiplier = 1 luhn_sum = template.gsub(/[^0-9]/, '').split('').reverse.map(&:to_i).inject(0) do |sum, digit| multiplier = (multiplier == 2 ? 1 : 2) sum + (digit * multiplier).to_s.split('').map(&:to_i).inject(0) { |digit_sum, cur| digit_sum + cur } end # the sum plus whatever the last digit is must be a multiple of 10. So, the # last digit must be 10 - the last digit of the sum. luhn_digit = (10 - (luhn_sum % 10)) % 10 template.gsub('L', luhn_digit.to_s) end