From: Jeffrey Moss <jeff@...>
Date: 2005-03-24T08:22:45+09:00
Subject: Credit Card Verification as an exercise

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Couldn't find any credit card verification code written in ruby so I =
wrote up my own.  This code turns out a lot smaller than the perl =
version I have been using.  I thought it was an interesting exercise, =
here is how its done, if anybody can improve on what I've done I'd be =
impressed.

Heres a howto guide on it
http://www.beachnet.com/~hstiles/cardtype.html

Feel free to use the code.




class CreditCard < ActiveRecord::Base

  def before_save
    if number_is_valid && number_matches_type
       ...
    end
  end

  def number_is_valid
    total =3D 0
    number.gsub(/[^0-9]/, '').reverse.scan(/(\d)(\d){0,1}/) do |ud,ad|
      (ad.to_i*2).to_s.each {|d| total =3D total + d.to_i} if ad
      total =3D total + ud.to_i
    end
    total % 10 =3D=3D 0 ? false : true
  end

  def number_matches_type
    digit_length =3D number.length
    if card_type =3D=3D 'visa'
      if (digit_length =3D=3D 16) || (digit_length =3D=3D 13)
        return true if number[/^\d/].to_i =3D=3D 4
      end
    elsif card_type =3D=3D 'mastercard'
      if digit_length =3D=3D 16
        return true if (51..55).to_a.include?(number[0..1].to_i)
      end
    elsif card_type =3D=3D 'amex'
      if digit_length =3D=3D 15
        return true if [34,37].include?(number[0..1].to_i)
      end
    elsif card_type =3D=3D 'discover'
      if digit_length =3D=3D 16
        return true if number[0..3].to_i =3D=3D 6011
      end
    end
  end
end


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