Sync icalendar to diary file

diary-sync-ical.el

;;; diary-sync-ical.el --- Sync iCalendar to diary   -*- lexical-binding: t; -*-

;; Copyright (C) 2015  Kan-Ru Chen (陳侃如)

;; Author: Kan-Ru Chen (陳侃如) <kanru@kanru.info>
;; Keywords: 

;; 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:

;; 

;;; Code:

(require 'cl-lib)
(require 'icalendar)
(require 'url)

(defvar diary-sync-ical-url "")
(defvar diary-sync-ical-dst "")

(defun diary-sync-ical--save-ical ()
  (set-buffer-multibyte t)
  (set-buffer-file-coding-system 'utf-8)
  (goto-char (point-min))
  (save-excursion
    (recode-region (point-min) (point-max) 'utf-8-dos 'utf-8-unix))
  (unless (icalendar-import-buffer
           (expand-file-name diary-sync-ical-dst) t nil)
    (warn "Unable to import icalendar. See *icalendar-errors* for details.")))

(defun diary-sync-ical (&optional sync)
  (interactive)
  (with-temp-file (expand-file-name diary-sync-ical-dst)
    (erase-buffer))
  (if sync
      (with-current-buffer
          (url-retrieve-synchronously diary-sync-ical-url)
        (diary-sync-ical--save-ical))
    (url-retrieve diary-sync-ical-url
                  (lambda (status &rest args)
                    (when (plist-get status :error)
                      (cl-destructuring-bind (error-symbol . data)
                          (plist-get status :error)
                        (signal error-symbol data)))
                    (diary-sync-ical--save-ical)))))

(provide 'diary-sync-ical)
;;; diary-sync-ical.el ends here