rails active_model validator for singapore nric & car plate; courtesy www.tinkerbox.com.sg

singapore_license_plate_validator.rb

class SingaporeLicensePlateValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, value)
    record.errors[attribute] << (options[:message] || "is not valid") unless valid_format?(value)
  end
  def valid_format?(license_plate)
    prefix, numbers, suffix = license_plate.to_s.upcase.gsub(/\W+/, '').scan(/^\s*([A-Z]{1,3})(\d{1,4})(.+)$/).flatten
    license_plate = ('%3s' % prefix.to_s) + ('%4d' % numbers.to_i) + suffix.to_s
    zero = ('A'.ord-1).chr
    numbers = []
    license_plate.each_char {|char| numbers.push((num = char.ord - zero.ord) > 0 ? num : char)}
    numbers = numbers.zip([3, 14, 2, 12, 2, 11, 1]).collect {|(a,b)| a.to_i * b.to_i }
    remainder = numbers.sum % 19
    'AYUSPLJGDBZXTRMKHEC'[remainder] == license_plate[-1]
  end
end

singapore_nric_validator.rb

# class Entity < ActiveRecord::Base
#   validates :name, presence: true, singapore_nric: true
# end

class SingaporeNricValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, value)
    record.errors[attribute] << (options[:message] || "is not valid") unless valid_format?(value)
  end
  def valid_format?(nric)
    nric = '%9s' % nric.to_s.upcase.gsub(/\W+/, '')
    numbers = []
    nric[1..7].to_s.each_char {|c| numbers.push(c.to_i) }
    total = numbers.zip([2, 7, 6, 5, 4, 3, 2]).collect {|(a,b)| a.to_i * b.to_i }.sum
    total += 4 if ['T', 'G'].include?(nric[0])
    remainder = total % 11
    result = (['S', 'T'].include?(nric[0]) ? 'JZIHGFEDCBA' : 'XWUTRQPNMLK')[remainder]
    result == nric[-1]
  end
end