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;;; sx-cache.el --- caching for stack-mode
;; Copyright (C) 2014 Sean Allred
;; Author: Sean Allred <code@seanallred.com>
;; This program is free software; you can redistribute it and/or modify
;; it under the terms of the GNU 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 General Public License
;; along with this program. If not, see <http://www.gnu.org/licenses/>.
;;; Commentary:
;; All caches are retrieved and set using symbols. The symbol should
;; be the sub-subpackage that is using the cache. For example,
;; `sx-pkg' would use `(sx-cache-get 'pkg)'.
;;
;; This symbol is then converted into a filename within
;; `sx-cache-directory'.
;;; Code:
(defcustom sx-cache-directory
(expand-file-name ".stackmode" user-emacs-directory)
"Directory containining cached data.")
(defun sx-cache--ensure-sx-cache-directory-exists ()
"Ensure `sx-cache-directory' exists."
(unless (file-exists-p sx-cache-directory)
(mkdir sx-cache-directory)))
(defun sx-cache-get-file-name (filename)
"Expand FILENAME in the context of `sx-cache-directory'."
(expand-file-name
(concat (symbol-name filename) ".el")
sx-cache-directory))
(defun sx-cache-get (cache &optional form)
"Return the data within CACHE.
If CACHE does not exist, use `sx-cache-set' to set CACHE to the
result of evaluating FORM.
CACHE is resolved to a file name by `sx-cache-get-file-name'."
(sx-cache--ensure-sx-cache-directory-exists)
(let ((file (sx-cache-get-file-name cache)))
;; If the file exists, return the data it contains
(if (file-exists-p file)
(with-temp-buffer
(insert-file-contents (sx-cache-get-file-name cache))
(read (buffer-string)))
;; Otherwise, set CACHE to the evaluation of FORM.
;; `sx-cache-set' returns the data that CACHE was set to.
(sx-cache-set cache (eval form)))))
(defun sx-cache-set (cache data)
"Set the content of CACHE to DATA and save changes permanently.
DATA will be written as returned by `prin1'.
CACHE is resolved to a file name by `sx-cache-get-file-name'."
(sx-cache--ensure-sx-cache-directory-exists)
(write-region (prin1-to-string data) nil
(sx-cache-get-file-name cache))
data)
(provide 'sx-cache)
;;; sx-cache.el ends here
;; Local Variables:
;; indent-tabs-mode: nil
;; End:
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