1 ;;; cal-iso.el --- calendar functions for the ISO calendar
3 ;; Copyright (C) 1995, 1997, 2001, 2002, 2003, 2004, 2005, 2006, 2007
4 ;; Free Software Foundation, Inc.
6 ;; Author: Edward M. Reingold <reingold@cs.uiuc.edu>
7 ;; Maintainer: Glenn Morris <rgm@gnu.org>
9 ;; Human-Keywords: ISO calendar, calendar, diary
11 ;; This file is part of GNU Emacs.
13 ;; GNU Emacs is free software; you can redistribute it and/or modify
14 ;; it under the terms of the GNU General Public License as published by
15 ;; the Free Software Foundation; either version 2, or (at your option)
18 ;; GNU Emacs is distributed in the hope that it will be useful,
19 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
20 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
21 ;; GNU General Public License for more details.
23 ;; You should have received a copy of the GNU General Public License
24 ;; along with GNU Emacs; see the file COPYING. If not, write to the
25 ;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
26 ;; Boston, MA 02110-1301, USA.
30 ;; This collection of functions implements the features of calendar.el and
31 ;; diary.el that deal with the ISO calendar.
33 ;; Technical details of all the calendrical calculations can be found in
34 ;; ``Calendrical Calculations: The Millennium Edition'' by Edward M. Reingold
35 ;; and Nachum Dershowitz, Cambridge University Press (2001).
37 ;; Comments, corrections, and improvements should be sent to
38 ;; Edward M. Reingold Department of Computer Science
39 ;; (217) 333-6733 University of Illinois at Urbana-Champaign
40 ;; reingold@cs.uiuc.edu 1304 West Springfield Avenue
41 ;; Urbana, Illinois 61801
49 (defun calendar-absolute-from-iso (date)
50 "The number of days elapsed between the Gregorian date 12/31/1 BC and DATE.
51 The `ISO year' corresponds approximately to the Gregorian year, but
52 weeks start on Monday and end on Sunday. The first week of the ISO year is
53 the first such week in which at least 4 days are in a year. The ISO
54 commercial DATE has the form (week day year) in which week is in the range
55 1..52 and day is in the range 0..6 (1 = Monday, 2 = Tuesday, ..., 0 =
56 Sunday). The Gregorian date Sunday, December 31, 1 BC is imaginary."
57 (let* ((week (extract-calendar-month date
))
58 (day (extract-calendar-day date
))
59 (year (extract-calendar-year date
)))
60 (+ (calendar-dayname-on-or-before
61 1 (+ 3 (calendar-absolute-from-gregorian (list 1 1 year
))))
63 (if (= day
0) 6 (1- day
)))))
65 (defun calendar-iso-from-absolute (date)
66 "Compute the `ISO commercial date' corresponding to the absolute DATE.
67 The ISO year corresponds approximately to the Gregorian year, but weeks
68 start on Monday and end on Sunday. The first week of the ISO year is the
69 first such week in which at least 4 days are in a year. The ISO commercial
70 date has the form (week day year) in which week is in the range 1..52 and
71 day is in the range 0..6 (1 = Monday, 2 = Tuesday, ..., 0 = Sunday). The
72 absolute date is the number of days elapsed since the (imaginary) Gregorian
73 date Sunday, December 31, 1 BC."
74 (let* ((approx (extract-calendar-year
75 (calendar-gregorian-from-absolute (- date
3))))
77 (calendar-sum y approx
78 (>= date
(calendar-absolute-from-iso (list 1 1 (1+ y
))))
81 (1+ (/ (- date
(calendar-absolute-from-iso (list 1 1 year
))) 7))
85 (defun calendar-iso-date-string (&optional date
)
86 "String of ISO date of Gregorian DATE.
87 Defaults to today's date if DATE is not given."
88 (let* ((d (calendar-absolute-from-gregorian
89 (or date
(calendar-current-date))))
91 (iso-date (calendar-iso-from-absolute d
)))
92 (format "Day %s of week %d of %d"
93 (if (zerop day
) 7 day
)
94 (extract-calendar-month iso-date
)
95 (extract-calendar-year iso-date
))))
97 (defun calendar-print-iso-date ()
98 "Show equivalent ISO date for the date under the cursor."
100 (message "ISO date: %s"
101 (calendar-iso-date-string (calendar-cursor-to-date t
))))
103 (defun calendar-iso-read-args (&optional dayflag
)
104 "Interactively read the arguments for an iso date command."
105 (let* ((today (calendar-current-date))
107 "ISO calendar year (>0): "
108 '(lambda (x) (> x
0))
109 (int-to-string (extract-calendar-year today
))))
110 (no-weeks (extract-calendar-month
111 (calendar-iso-from-absolute
113 (calendar-dayname-on-or-before
114 1 (calendar-absolute-from-gregorian
115 (list 1 4 (1+ year
))))))))
117 (format "ISO calendar week (1-%d): " no-weeks
)
118 '(lambda (x) (and (> x
0) (<= x no-weeks
)))))
119 (day (if dayflag
(calendar-read
121 '(lambda (x) (and (<= 1 x
) (<= x
7))))
123 (list (list week day year
))))
125 (defun calendar-goto-iso-date (date &optional noecho
)
126 "Move cursor to ISO DATE; echo ISO date unless NOECHO is t."
127 (interactive (calendar-iso-read-args t
))
128 (calendar-goto-date (calendar-gregorian-from-absolute
129 (calendar-absolute-from-iso date
)))
130 (or noecho
(calendar-print-iso-date)))
132 (defun calendar-goto-iso-week (date &optional noecho
)
133 "Move cursor to ISO DATE; echo ISO date unless NOECHO is t.
134 Interactively, goes to the first day of the specified week."
135 (interactive (calendar-iso-read-args))
136 (calendar-goto-date (calendar-gregorian-from-absolute
137 (calendar-absolute-from-iso date
)))
138 (or noecho
(calendar-print-iso-date)))
140 (defun diary-iso-date ()
141 "ISO calendar equivalent of date diary entry."
142 (format "ISO date: %s" (calendar-iso-date-string date
)))
146 ;;; arch-tag: 3c0154cc-d30f-4981-9f60-42bdf7a468f6
147 ;;; cal-iso.el ends here