1;;; cal-iso.el --- calendar functions for the ISO calendar 2 3;; Copyright (C) 1995, 1997, 2001, 2002, 2003, 2004, 2005, 2006, 2007 4;; Free Software Foundation, Inc. 5 6;; Author: Edward M. Reingold <reingold@cs.uiuc.edu> 7;; Maintainer: Glenn Morris <rgm@gnu.org> 8;; Keywords: calendar 9;; Human-Keywords: ISO calendar, calendar, diary 10 11;; This file is part of GNU Emacs. 12 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) 16;; any later version. 17 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. 22 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. 27 28;;; Commentary: 29 30;; This collection of functions implements the features of calendar.el and 31;; diary.el that deal with the ISO calendar. 32 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). 36 37;;; Code: 38 39(defvar date) 40 41(require 'calendar) 42 43(defun calendar-absolute-from-iso (date) 44 "The number of days elapsed between the Gregorian date 12/31/1 BC and DATE. 45The `ISO year' corresponds approximately to the Gregorian year, but 46weeks start on Monday and end on Sunday. The first week of the ISO year is 47the first such week in which at least 4 days are in a year. The ISO 48commercial DATE has the form (week day year) in which week is in the range 491..52 and day is in the range 0..6 (1 = Monday, 2 = Tuesday, ..., 0 = 50Sunday). The Gregorian date Sunday, December 31, 1 BC is imaginary." 51 (let* ((week (extract-calendar-month date)) 52 (day (extract-calendar-day date)) 53 (year (extract-calendar-year date))) 54 (+ (calendar-dayname-on-or-before 55 1 (+ 3 (calendar-absolute-from-gregorian (list 1 1 year)))) 56 (* 7 (1- week)) 57 (if (= day 0) 6 (1- day))))) 58 59(defun calendar-iso-from-absolute (date) 60 "Compute the `ISO commercial date' corresponding to the absolute DATE. 61The ISO year corresponds approximately to the Gregorian year, but weeks 62start on Monday and end on Sunday. The first week of the ISO year is the 63first such week in which at least 4 days are in a year. The ISO commercial 64date has the form (week day year) in which week is in the range 1..52 and 65day is in the range 0..6 (1 = Monday, 2 = Tuesday, ..., 0 = Sunday). The 66absolute date is the number of days elapsed since the (imaginary) Gregorian 67date Sunday, December 31, 1 BC." 68 (let* ((approx (extract-calendar-year 69 (calendar-gregorian-from-absolute (- date 3)))) 70 (year (+ approx 71 (calendar-sum y approx 72 (>= date (calendar-absolute-from-iso (list 1 1 (1+ y)))) 73 1)))) 74 (list 75 (1+ (/ (- date (calendar-absolute-from-iso (list 1 1 year))) 7)) 76 (% date 7) 77 year))) 78 79(defun calendar-iso-date-string (&optional date) 80 "String of ISO date of Gregorian DATE. 81Defaults to today's date if DATE is not given." 82 (let* ((d (calendar-absolute-from-gregorian 83 (or date (calendar-current-date)))) 84 (day (% d 7)) 85 (iso-date (calendar-iso-from-absolute d))) 86 (format "Day %s of week %d of %d" 87 (if (zerop day) 7 day) 88 (extract-calendar-month iso-date) 89 (extract-calendar-year iso-date)))) 90 91(defun calendar-print-iso-date () 92 "Show equivalent ISO date for the date under the cursor." 93 (interactive) 94 (message "ISO date: %s" 95 (calendar-iso-date-string (calendar-cursor-to-date t)))) 96 97(defun calendar-iso-read-args (&optional dayflag) 98 "Interactively read the arguments for an iso date command." 99 (let* ((today (calendar-current-date)) 100 (year (calendar-read 101 "ISO calendar year (>0): " 102 '(lambda (x) (> x 0)) 103 (int-to-string (extract-calendar-year today)))) 104 (no-weeks (extract-calendar-month 105 (calendar-iso-from-absolute 106 (1- 107 (calendar-dayname-on-or-before 108 1 (calendar-absolute-from-gregorian 109 (list 1 4 (1+ year)))))))) 110 (week (calendar-read 111 (format "ISO calendar week (1-%d): " no-weeks) 112 '(lambda (x) (and (> x 0) (<= x no-weeks))))) 113 (day (if dayflag (calendar-read 114 "ISO day (1-7): " 115 '(lambda (x) (and (<= 1 x) (<= x 7)))) 116 1))) 117 (list (list week day year)))) 118 119(defun calendar-goto-iso-date (date &optional noecho) 120 "Move cursor to ISO DATE; echo ISO date unless NOECHO is t." 121 (interactive (calendar-iso-read-args t)) 122 (calendar-goto-date (calendar-gregorian-from-absolute 123 (calendar-absolute-from-iso date))) 124 (or noecho (calendar-print-iso-date))) 125 126(defun calendar-goto-iso-week (date &optional noecho) 127 "Move cursor to ISO DATE; echo ISO date unless NOECHO is t. 128Interactively, goes to the first day of the specified week." 129 (interactive (calendar-iso-read-args)) 130 (calendar-goto-date (calendar-gregorian-from-absolute 131 (calendar-absolute-from-iso date))) 132 (or noecho (calendar-print-iso-date))) 133 134(defun diary-iso-date () 135 "ISO calendar equivalent of date diary entry." 136 (format "ISO date: %s" (calendar-iso-date-string date))) 137 138(provide 'cal-iso) 139 140;;; arch-tag: 3c0154cc-d30f-4981-9f60-42bdf7a468f6 141;;; cal-iso.el ends here 142