CC Validation

README.md

Example Usage -- use ruby 1.9.3

git clone git@gist.github.com:3713188.git ccvalidator

cd ccvalidator

cat input1.dat | ./validate_cards.rb

ruby test/credit_card_validator_spec.rb

credit_card_validator.rb

# note -- assumption is that an Unknown type of card is invalid, regardless of the luhn validity
# I also consider a card to be of Unknown type if the length doesn't match the valid length for a given prefix

class CreditCardValidator
  attr_accessor :cardnum
  def initialize(cardnum)
    #remove spaces and dashes -- possibly should remove all non-digit characters?
    @cardnum = cardnum.gsub(/[\s-]/, '')
  end
  # check prefix digits and length
  def card_type
    return 'AMEX' if ['34','37'].include?(@cardnum[0..1]) && @cardnum.length == 15
    return 'Discover' if @cardnum[0..3] == '6011' && @cardnum.length == 16
    return 'MasterCard' if ['51','52','53','54','55'].include?(@cardnum[0..1]) && @cardnum.length == 16
    return 'VISA' if @cardnum[0..0] == '4' && [13,16].include?(@cardnum.length)
    return 'Unknown'
  end

  def type_and_number
    "#{card_type}: #{cardnum}"
  end

  # check that the card number matches the luhn algorithm
  def valid_luhn
    # for odd length card numbers, we want to start by doubling the second digit instead of the first one
    offset = (@cardnum.length + 1) % 2
    expanded_string = ''
    @cardnum.chars.each_with_index do |char, index|
      # double every other digit
      new_char = char.to_i * ((index + offset) % 2 + 1)
      expanded_string += new_char.to_s
    end
    sum_of_chars = expanded_string.chars.inject(0) do |result, char|
      result += char.to_i
    end
    return (sum_of_chars % 10) == 0
  end

  def valid
    return card_type != 'Unknown' && valid_luhn
  end

  def printable_valid
    valid ? 'valid' : 'invalid'
  end

  def self.process_stream(istream)
    while !istream.eof && line = istream.readline
      validator = CreditCardValidator.new(line.strip)
      yield "#{validator.type_and_number.ljust(28)} (#{validator.printable_valid})"
    end
  end
end

credit_card_validator_spec.rb

require 'minitest/autorun'
require 'stringio'
require_relative '../credit_card_validator.rb'

describe "CreditCardValidator", "Complete credit card validation tests" do
  it "validates AMEX cards" do
    #test valid cases
    validator = CreditCardValidator.new("378282246310005")
    validator.card_type.must_equal 'AMEX'
    validator.valid.must_equal true
    validator = CreditCardValidator.new("348282246310002")
    validator.card_type.must_equal 'AMEX'
    validator.valid.must_equal true
    validator = CreditCardValidator.new("378282246310005")
    validator.card_type.must_equal 'AMEX'
    validator.valid.must_equal true
    #test invalid prefix
    validator = CreditCardValidator.new("358282246310017")
    validator.card_type.must_equal 'Unknown'
    validator.valid_luhn.must_equal true
    validator.valid.must_equal false
    #test invalid luhn
    validator = CreditCardValidator.new("348282246310016")
    validator.card_type.must_equal 'AMEX'
    validator.valid.must_equal false
    #test invalid length
    validator = CreditCardValidator.new("358282246310017")
    validator.card_type.must_equal 'Unknown'
    validator.valid_luhn.must_equal true
    validator.valid.must_equal false
  end

  it "validates Mastercards" do
    #test valid cases
    validator = CreditCardValidator.new("5103195004195007")
    validator.card_type.must_equal 'MasterCard'
    validator.valid.must_equal true
    validator = CreditCardValidator.new("5203195004195006")
    validator.card_type.must_equal 'MasterCard'
    validator.valid.must_equal true
    validator = CreditCardValidator.new("5303195004195005")
    validator.card_type.must_equal 'MasterCard'
    validator.valid.must_equal true
    validator = CreditCardValidator.new("5403195004195004")
    validator.card_type.must_equal 'MasterCard'
    validator.valid.must_equal true
    validator = CreditCardValidator.new("5503195004195003")
    validator.card_type.must_equal 'MasterCard'
    validator.valid.must_equal true
    #test invalid prefix
    validator = CreditCardValidator.new("5003195004195008")
    validator.card_type.must_equal 'Unknown'
    validator.valid_luhn.must_equal true
    validator.valid.must_equal false
    #test invalid luhn
    validator = CreditCardValidator.new("5503195004195004")
    validator.card_type.must_equal 'MasterCard'
    validator.valid.must_equal false
    #test invalid length
    validator = CreditCardValidator.new("55031950041953")
    validator.card_type.must_equal 'Unknown'
    validator.valid_luhn.must_equal true
    validator.valid.must_equal false
  end

  it "validates Discover cards" do
    #test valid cases
    validator = CreditCardValidator.new("6011111111111109")
    validator.card_type.must_equal 'Discover'
    validator.valid.must_equal true
    #test invalid prefix
    validator = CreditCardValidator.new("7011111111111107")
    validator.card_type.must_equal 'Unknown'
    validator.valid_luhn.must_equal true
    validator.valid.must_equal false
    #test invalid luhn
    validator = CreditCardValidator.new("6011111111111119")
    validator.card_type.must_equal 'Discover'
    validator.valid.must_equal false
    #test invalid length
    validator = CreditCardValidator.new("60111111111110")
    validator.card_type.must_equal 'Unknown'
    validator.valid_luhn.must_equal true
    validator.valid.must_equal false
  end

  it "validates Visa cards" do
    #test valid cases
    validator = CreditCardValidator.new("4211111111111110")
    validator.card_type.must_equal 'VISA'
    validator.valid.must_equal true
    validator = CreditCardValidator.new("4211 1111 1111 1110")
    validator.card_type.must_equal 'VISA'
    validator.valid.must_equal true
    validator = CreditCardValidator.new("4211-1111-1111-1110")
    validator.card_type.must_equal 'VISA'
    validator.valid.must_equal true
    validator = CreditCardValidator.new("4000000000006")
    validator.card_type.must_equal 'VISA'
    validator.valid.must_equal true
    #test invalid prefix
    validator = CreditCardValidator.new("3111111111111113")
    validator.card_type.must_equal 'Unknown'
    validator.valid_luhn.must_equal true
    validator.valid.must_equal false
    #test invalid luhn
    validator = CreditCardValidator.new("4111111111111110")
    validator.card_type.must_equal 'VISA'
    validator.valid.must_equal false
    #test invalid length
    validator = CreditCardValidator.new("400000000002")
    validator.card_type.must_equal 'Unknown'
    validator.valid_luhn.must_equal true
    validator.valid.must_equal false
  end
  it "processes streams correctly" do
    inputfile = StringIO.new("4111111111111111\n4111111111111\n4012888888881881\n378282246310005\n6011111111111117\n5105105105105100\n5105 1051 0510 5106\n9111111111111111\n")
    outputfile = StringIO.new("VISA: 4111111111111111       (valid)\nVISA: 4111111111111          (invalid)\nVISA: 4012888888881881       (valid)\nAMEX: 378282246310005        (valid)\nDiscover: 6011111111111117   (valid)\nMasterCard: 5105105105105100 (valid)\nMasterCard: 5105105105105106 (invalid)\nUnknown: 9111111111111111    (invalid)\n")
    result = CreditCardValidator.process_stream(inputfile) do |line|
      line.must_equal outputfile.readline.strip
    end
  end
end

input1.dat

4111111111111111
4111111111111
4012888888881881
378282246310005
6011111111111117
5105105105105100
5105 1051 0510 5106
9111111111111111

validate_cards.rb

#!/usr/bin/env ruby
require_relative 'credit_card_validator'

CreditCardValidator.process_stream(STDIN) do |result|
  STDOUT << result << "\n"
end