passport.rb

# see http://en.wikipedia.org/wiki/Machine-readable_passport

def checksum(str)
  arr = str.split("")
  count = 1
  result = 0
  arr.each do |n|
    num = nil
    factor = 0
    if(count%3==1)
      factor = 7
      num = n.to_i*factor
    end
    if(count%3==2)
      factor = 3
      num = n.to_i*factor
    end
    if(count%3==0)
      factor = 1
      num = n.to_i*factor
    end
    count = count + 1
    result = result + num
  end
  return result%10
end

if(!ARGV || ARGV.length<3 || ARGV[0].length != 9 || ARGV[1].length != 6 || ARGV[2].length !=6)
  puts "usage: ruby passport.rb 123456789 YYMMDD YYMMDD"
else
  first_checksum = checksum(ARGV[0])
  second_checksum = checksum(ARGV[1])
  third_checksum = checksum(ARGV[2])

  final_checksum = checksum("#{ARGV[0]}#{first_checksum}#{ARGV[1]}#{second_checksum}#{ARGV[2]}#{third_checksum}")
  str = "#{ARGV[0]}#{first_checksum}GBR#{ARGV[1]}#{second_checksum}<#{ARGV[2]}#{third_checksum}<<<<<<<<<<<<<<0#{final_checksum}"
  puts str
  puts str.length
end