;;; varuga.el --- Send ical calendar invites by email -*- lexical-binding: t -*-
;; Send ical calendar invites by email
;; Copyright © 2021–2024 Arun Isaac
;;
;; Author: Arun Isaac <arunisaac@systemreboot.net>
;; Version: 0.1.0
;; Homepage: https://git.systemreboot.net/varuga
;; Package-Requires: ((emacs "26.1"))
;; This file is part of varuga.
;; varuga 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.
;; varuga 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 varuga. If not, see <http://www.gnu.org/licenses/>.
;;; Commentary:
;;
;; Send ical calendar invites using your Emacs mail client. These
;; invites are similar to those produced by Google Calendar, Outlook
;; Calendar, etc. and are compatible with them.
;;
;; varuga populates a message mode buffer with an ical MIME part
;; (using MML, the MIME Meta Language). It also adds a plain text
;; part listing the time of the event in various configured timezones.
;;
;; All dates and times you enter into varuga are in your local
;; timezone. varuga automatically converts these into a set of
;; configured timezones (specified in `varuga-clock-list`) for your
;; correspondents' benefit.
;;
;; 🙏 வருக வருக! (varuga varuga!) is a Tamil expression that is used
;; to warmly welcome people to an event.
;;; Code:
(require 'cl-lib)
(require 'message)
(require 'org)
(require 'org-duration)
(require 'org-id)
(require 'time)
(cl-defstruct (varuga-calendar (:constructor varuga-calendar)
(:copier nil))
components)
(cl-defstruct (varuga-calendar-event (:constructor varuga-calendar-event)
(:copier nil))
organizer
organizer-email-address
time-start
time-end
summary
location)
(defvar varuga-product-identifier
"-//systemreboot//varuga//NONSGML v1.0//EN")
(defvar varuga-clock-list
(if (listp world-clock-list)
world-clock-list
zoneinfo-style-world-list))
(defvar varuga-time-format
world-clock-time-format)
(defun varuga-insert-calendar-line (key value)
"Insert ical calendar line.
KEY is the name of the ical property and VALUE is its value."
;; Limit content line length to 75 octets as required by RFC 5545.
(let ((maximum-octets-per-line 75)
(octets-so-far 0))
(seq-do (lambda (c)
(let* (;; Escape the linefeed character.
(str (if (eql c ?\n)
"\\N"
(string c)))
(next-octets (+ octets-so-far
(string-bytes str))))
(if (< next-octets maximum-octets-per-line)
(progn
(insert str)
(setq octets-so-far next-octets))
(insert "\n ")
;; Set octets so far to 1 to account for the
;; folding space.
(setq octets-so-far 1))))
(format "%s:%s"
(upcase (symbol-name key))
value)))
(insert "\n"))
(defun varuga-format-time-string (time)
"Format TIME to ical specification."
(format-time-string "%Y%m%dT%H%M%SZ" time t))
(defun varuga-insert-calendar-event (event)
"Insert ical calendar EVENT at point."
(varuga-insert-calendar-line 'begin "VEVENT")
(varuga-insert-calendar-line 'uid (org-id-uuid))
(varuga-insert-calendar-line 'organizer
(format "CN=%s:MAILTO:%s"
(varuga-calendar-event-organizer event)
(varuga-calendar-event-organizer-email-address event)))
(varuga-insert-calendar-line 'dtstart
(varuga-format-time-string
(varuga-calendar-event-time-start event)))
(varuga-insert-calendar-line 'dtend
(varuga-format-time-string
(varuga-calendar-event-time-end event)))
(varuga-insert-calendar-line 'summary
(varuga-calendar-event-summary event))
(varuga-insert-calendar-line 'location
(varuga-calendar-event-location event))
(varuga-insert-calendar-line 'end "VEVENT"))
(defun varuga-insert-calendar (calendar)
"Insert ical CALENDAR at point."
(varuga-insert-calendar-line 'begin "VCALENDAR")
(varuga-insert-calendar-line 'version "2.0")
(varuga-insert-calendar-line 'prodid varuga-product-identifier)
(seq-do #'varuga-insert-calendar-event
(varuga-calendar-components calendar))
(varuga-insert-calendar-line 'end "VCALENDAR"))
(defun varuga-message-subject ()
"Return subject of message."
(or (message-fetch-field "Subject")
""))
(defun varuga-invite (summary location when duration)
"Insert calendar invitation into current email message buffer.
SUMMARY is a short description of the event. LOCATION is the
location of the event (typically a URI for online meetings).
WHEN is the encoded time when the event is scheduled. DURATION
is the length of the event in minutes."
(interactive (list (read-string "Event Summary: "
(string-trim
(string-remove-prefix
"Re:" (varuga-message-subject))))
(read-string "Location: ")
(org-read-date t t nil "When?")
(org-duration-to-minutes
(read-string "Duration: " "1h"))))
(save-excursion
;; Fill Subject header if it is blank.
(when (string-blank-p (varuga-message-subject))
(save-restriction
(message-narrow-to-headers)
(re-search-forward "^Subject:")
(message-narrow-to-field)
(end-of-line)
;; TODO: Allow customization of the Subject format.
(insert (format "Invitation: %s" summary))))
;; Fill email body.
(goto-char (point-max))
(insert "<#multipart type=mixed>\n")
;; Add human-readable time in configured timezones. TODO: Allow
;; customization of this format.
(insert "<#part type=text/plain>\n\n")
(seq-do (pcase-lambda (`(,zone ,place))
(insert place)
(insert " — ")
(insert (let ((system-time-locale "C"))
(format-time-string varuga-time-format when zone)))
(insert "\n"))
varuga-clock-list)
;; Insert ical part.
(insert "<#part type=text/calendar>\n")
(varuga-insert-calendar
(varuga-calendar
:components (list (pcase (mail-extract-address-components
(message-fetch-field "From"))
(`(,organizer ,organizer-email-address)
(varuga-calendar-event
:organizer organizer
:organizer-email-address organizer-email-address
:time-start when
:time-end (time-add when
(* 60 (org-duration-to-minutes duration)))
:summary summary
:location location))))))
(insert "<#/multipart>\n")))
(provide 'varuga)
;;; varuga.el ends here
