require 'rails_generator/secret_key_generator'

module TokenGenerator
  def generate_token(size = 32, &validity)
    constant = "#{self.class.name}#{id}"
    generator = Rails::SecretKeyGenerator.new(constant)

    begin
      token = generator.generate_secret.first(size)
    end while !validity.call(token) if block_given?

    token
  end
end