;; persistent-cache.lisp --- 

;; Copyright (C) 2008 Clinton Ebadi <clinton@unknownlamer.org>

;; Author: Clinton Ebadi <clinton@unknownlamer.org>

;; This program is free software: you can redistribute it and/or modify
;; it under the terms of the GNU Lesser General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; This program is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU Lesser General Public License
;; along with this program.  If not, see <http://www.gnu.org/licenses/>.

(in-package :org.unknownlamer.golgonooza.elephant)

(defpclass cacheable-persistent-object ()
  ((object-hash :initform nil :accessor object-hash)))

(defpclass persistent-cache-item ()
  ((instance :initarg :instance :accessor cached-instance :index t)
   (%hash :accessor cached-hash)
   (%cache :accessor cached-cache)))

(defmethod cache-valid-p ((c persistent-cache-item))
  (equalp (cached-hash c) (object-hash (cached-instance c))))

(defgeneric update-cache! (persistent-cache-item instance))

(defun find-cached-instance (instance &key (cache-class 'persistent-cache-item))
  (or (get-instance-by-value cache-class 'instance instance)
      (make-instance cache-class :instance instance)))

(defmethod (setf cached-cache) :after (new (c persistent-cache-item))
  (setf (cached-hash c) (object-hash (cached-instance c))))

;; update-cache! p-c-i new-cache instead?
(defmethod update-cache! :around ((c persistent-cache-item) (i cacheable-persistent-object))
  (setf (cached-cache c) (call-next-method)))

(defmethod initialize-instance :after ((c persistent-cache-item)
				       &key instance &allow-other-keys)
  (when instance
    (update-cache! c (cached-instance c))))