class Tan < ActiveRecord::Base
  DEFAULT_EXPIRE_TIME = 5.minutes
  validates_presence_of :value, :expires_at

  def self.generate(expire_in = nil)    
    expires_at = Time.now + (expire_in || DEFAULT_EXPIRE_TIME)
    create(:expires_at => expires_at).value
  end

  def self.spend(value)
    delete_expired!
    if tan = find_by_value(value) rescue nil
      tan.destroy
      value
    else
      nil    
    end
  end

  protected
    def before_validation_on_create
      self.value = Digest::SHA1.hexdigest(Randomizer.string)      
      self.expires_at ||= (Time.now + DEFAULT_EXPIRE_TIME)
    end

    def self.delete_expired!
      Tan.delete_all(['expires_at < ?', Time.now])      
    end


end