lisp/calendar/cal-iso.el

   1 ;;; cal-iso.el --- calendar functions for the ISO calendar
   2
   3 ;; Copyright (C) 1995, 1997, 2001-2015 Free Software Foundation, Inc.
   4
   5 ;; Author: Edward M. Reingold <reingold@cs.uiuc.edu>
   6 ;; Maintainer: Glenn Morris <rgm@gnu.org>
   7 ;; Keywords: calendar
   8 ;; Human-Keywords: ISO calendar, calendar, diary
   9 ;; Package: calendar
  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 3 of the License, or
  16 ;; (at your option) 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.  If not, see <http://www.gnu.org/licenses/>.
  25
  26 ;;; Commentary:
  27
  28 ;; See calendar.el.
  29
  30 ;;; Code:
  31
  32 (require 'calendar)
  33
  34 (defun calendar-iso-to-absolute (date)
  35   "The number of days elapsed between the Gregorian date 12/31/1 BC and DATE.
  36 The `ISO year' corresponds approximately to the Gregorian year, but
  37 weeks start on Monday and end on Sunday.  The first week of the ISO year is
  38 the first such week in which at least 4 days are in a year.  The ISO
  39 commercial DATE has the form (week day year) in which week is in the range
  40 1..52 and day is in the range 0..6 (1 = Monday, 2 = Tuesday, ..., 0 =
  41 Sunday).  The Gregorian date Sunday, December 31, 1 BC is imaginary."
  42   (let ((day (calendar-extract-day date)))
  43     (+ (calendar-dayname-on-or-before
  44         1 (+ 3 (calendar-absolute-from-gregorian
  45                 (list 1 1 (calendar-extract-year date)))))
  46        ;; ISO date is (week day year); normally (month day year).
  47        (* 7 (1- (calendar-extract-month date)))
  48        (if (zerop day) 6 (1- day)))))
  49
  50 ;;;###cal-autoload
  51 (defun calendar-iso-from-absolute (date)
  52   "Compute the `ISO commercial date' corresponding to the absolute DATE.
  53 The ISO year corresponds approximately to the Gregorian year, but weeks
  54 start on Monday and end on Sunday.  The first week of the ISO year is the
  55 first such week in which at least 4 days are in a year.  The ISO commercial
  56 date has the form (week day year) in which week is in the range 1..52 and
  57 day is in the range 0..6 (1 = Monday, 2 = Tuesday, ..., 0 = Sunday).  The
  58 absolute date is the number of days elapsed since the (imaginary) Gregorian
  59 date Sunday, December 31, 1 BC."
  60   (let* ((approx (calendar-extract-year
  61                   (calendar-gregorian-from-absolute (- date 3))))
  62          (year (+ approx
  63                   (calendar-sum y approx
  64                                 (>= date (calendar-iso-to-absolute
  65                                           (list 1 1 (1+ y))))
  66                                 1))))
  67     (list
  68      (1+ (/ (- date (calendar-iso-to-absolute (list 1 1 year))) 7))
  69      (% date 7)
  70      year)))
  71
  72 ;;;###cal-autoload
  73 (defun calendar-iso-date-string (&optional date)
  74   "String of ISO date of Gregorian DATE, default today."
  75   (let* ((d (calendar-absolute-from-gregorian
  76              (or date (calendar-current-date))))
  77          (day (% d 7))
  78          (iso-date (calendar-iso-from-absolute d)))
  79     (format "Day %s of week %d of %d"
  80             (if (zerop day) 7 day)
  81             (calendar-extract-month iso-date)
  82             (calendar-extract-year iso-date))))
  83
  84 ;;;###cal-autoload
  85 (defun calendar-iso-print-date ()
  86   "Show equivalent ISO date for the date under the cursor."
  87   (interactive)
  88   (message "ISO date: %s"
  89            (calendar-iso-date-string (calendar-cursor-to-date t))))
  90
  91 (defun calendar-iso-read-date (&optional dayflag)
  92   "Interactively read the arguments for an ISO date command.
  93 Reads a year and week, and if DAYFLAG is non-nil a day (otherwise
  94 taken to be 1)."
  95   (let* ((year (calendar-read
  96                 "ISO calendar year (>0): "
  97                 (lambda (x) (> x 0))
  98                 (number-to-string (calendar-extract-year
  99                                 (calendar-current-date)))))
 100          (no-weeks (calendar-extract-month
 101                     (calendar-iso-from-absolute
 102                      (1-
 103                       (calendar-dayname-on-or-before
 104                        1 (calendar-absolute-from-gregorian
 105                           (list 1 4 (1+ year))))))))
 106          (week (calendar-read
 107                 (format "ISO calendar week (1-%d): " no-weeks)
 108                 (lambda (x) (and (> x 0) (<= x no-weeks)))))
 109          (day (if dayflag (calendar-read
 110                            "ISO day (1-7): "
 111                            (lambda (x) (and (<= 1 x) (<= x 7))))
 112                 1)))
 113     (list (list week day year))))
 114
 115 ;;;###cal-autoload
 116 (defun calendar-iso-goto-date (date &optional noecho)
 117   "Move cursor to ISO DATE; echo ISO date unless NOECHO is non-nil."
 118   (interactive (calendar-iso-read-date t))
 119   (calendar-goto-date (calendar-gregorian-from-absolute
 120                        (calendar-iso-to-absolute date)))
 121   (or noecho (calendar-iso-print-date)))
 122
 123 ;;;###cal-autoload
 124 (defun calendar-iso-goto-week (date &optional noecho)
 125   "Move cursor to ISO DATE; echo ISO date unless NOECHO is non-nil.
 126 Interactively, goes to the first day of the specified week."
 127   (interactive (calendar-iso-read-date))
 128   (calendar-goto-date (calendar-gregorian-from-absolute
 129                        (calendar-iso-to-absolute date)))
 130   (or noecho (calendar-iso-print-date)))
 131
 132 (defvar date)
 133
 134 ;; To be called from diary-list-sexp-entries, where DATE is bound.
 135 ;;;###diary-autoload
 136 (defun diary-iso-date ()
 137   "ISO calendar equivalent of date diary entry."
 138   (format "ISO date: %s" (calendar-iso-date-string date)))
 139
 140 (provide 'cal-iso)
 141
 142 ;;; cal-iso.el ends here