From: Bryan Weatherly <bryan.weatherly.ruby@...>
Date: 2007-04-30T03:39:47+09:00
Subject: Re: [QUIZ] Checking Credit Cards (#122)

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This is my first quiz submission.  The only testing I did was running the
cards I had in my wallet.  It seems to work.  I'm sure there's a much better
way to implement this, but here it is:

#card_check.rb

def check_type(number)
  #Returns a string representing the type of card if the length and
leading
  #  digits are valid.  Otherwise returns "Unknown".
  valid = {
    /^(34|37)/ => [15,"AMEX"],
    /^6011/ => [16,"Discover"],
    /^(51|52|53|54|55)/ => [16,"MasterCard"],
    /^4/ => [13,16,"Visa"]
  }
  number.gsub!(/ /,"")
  valid.each_key do |i|
    if number =~ i
      return valid[i][-1] if valid[i].include? number.length
    end
  end
  return "Unknown"
end

def luhn(number)
  # Returns "valid" if the number passes the Luhn algorihm criteria.
Returns
  #   "invalid" if the algorithm fails.
  number = number.gsub(/ /,"").split(//).reverse
  new_number = ""
  number.each_index do |i|
    new_number << (number[i].to_i*2).to_s if (i+1) % 2 == 0
    new_number << number[i] if (i+1) % 2 == 1
  end
  new_number = new_number.split(//)
  sum = 0
  new_number.each_index { |i| sum += new_number[i].to_i }
  return "valid" if sum % 10 == 0 unless number.length == 0
  return "invalid"
end

def validate_card(number)
  puts "Type:   #{check_type(number)}"
  puts "Status: #{luhn(number)}"
end

validate_card(ARGV.join("")) if __FILE__ == $0

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