make_pnr.rb

# Generator for valid Swedish personnummer: http://en.wikipedia.org/wiki/Personal_identity_number_(Sweden)
# By Henrik Nyh <http://henrik.nyh.se> 2009-01-29 under the MIT license.

require 'date'

def make_pnr(date=nil, serial=nil)
  date ||= Date.new(1900+rand(100), 1+rand(12), 1+rand(28))
  serial = serial ? serial.to_s : format("%03d", rand(999)+1)  # 001-999

  date_part = date.strftime('%y%m%d')
  pnr = [date_part, serial].join
  
  digits = []
  pnr.split('').each_with_index do |n,i|
    digits << n.to_i * (2 - i % 2)
  end
  sum = digits.join.split('').inject(0) {|sum,digit| sum += digit.to_i }
  checksum = 10 - sum % 10
  checksum = 0 if checksum == 10
  "#{date_part}-#{serial}#{checksum}"
end

if $0 == __FILE__
  # Randomize every part
  puts make_pnr
  # Use given date, randomize serial
  puts make_pnr(Date.new(1975,1,1))
  # Use given date and serial, calculate checksum
  puts make_pnr(Date.new(1975,1,1), 123)
end