permalink_fu: create_unique_permalink method

  def create_unique_permalink
    return unless should_create_permalink?
    if send(self.class.permalink_field).to_s.empty?
      send("#{self.class.permalink_field}=", create_permalink_for(self.class.permalink_attributes))
    end
    limit   = self.class.columns_hash[self.class.permalink_field].limit
    base    = send("#{self.class.permalink_field}=", send(self.class.permalink_field)[0..limit - 1])
    counter = 1
    # oh how i wish i could use a hash for conditions
    conditions = ["#{self.class.permalink_field} = ?", base]
    unless new_record?
      conditions.first << " and id != ?"
      conditions       << id
    end
    if self.class.permalink_options[:scope]
      conditions.first << " and #{self.class.permalink_options[:scope]} = ?"
      conditions       << send(self.class.permalink_options[:scope])
    end
    if should_create_unique_permalink?
      while self.class.exists?(conditions)
        suffix = "-#{counter += 1}"
        conditions[1] = "#{base[0..limit-suffix.size-1]}#{suffix}"
        send("#{self.class.permalink_field}=", conditions[1])
      end
    end
  end