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212 lines
8.4 KiB
EmacsLisp
212 lines
8.4 KiB
EmacsLisp
;;; cal-julian.el --- calendar functions for the Julian calendar -*- lexical-binding:t -*-
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;; Copyright (C) 1995, 1997, 2001-2024 Free Software Foundation, Inc.
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;; Author: Edward M. Reingold <reingold@cs.uiuc.edu>
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;; Maintainer: emacs-devel@gnu.org
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;; Keywords: calendar
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;; Human-Keywords: Julian calendar, Julian day number, calendar, diary
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;; Package: calendar
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;; This file is part of GNU Emacs.
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;; GNU Emacs is free software: you can redistribute it and/or modify
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;; it under the terms of the GNU General Public License as published by
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;; the Free Software Foundation, either version 3 of the License, or
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;; (at your option) any later version.
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;; GNU Emacs is distributed in the hope that it will be useful,
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;; but WITHOUT ANY WARRANTY; without even the implied warranty of
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;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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;; GNU General Public License for more details.
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;; You should have received a copy of the GNU General Public License
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;; along with GNU Emacs. If not, see <https://www.gnu.org/licenses/>.
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;;; Commentary:
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;; See calendar.el.
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;;; Code:
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(require 'calendar)
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(defun calendar-julian-to-absolute (date)
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"The number of days elapsed between the Gregorian date 12/31/1 BC and DATE.
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The Gregorian date Sunday, December 31, 1 BC is imaginary."
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(let ((month (calendar-extract-month date))
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(year (calendar-extract-year date)))
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(+ (calendar-day-number date)
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(if (and (zerop (% year 100))
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(not (zerop (% year 400)))
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(> month 2))
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1 0) ; correct for Julian but not Gregorian leap year
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(* 365 (1- year))
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(/ (1- year) 4)
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-2)))
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;;;###cal-autoload
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(defun calendar-julian-from-absolute (date)
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"Compute the Julian (month day year) corresponding to the absolute DATE.
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The absolute date is the number of days elapsed since the (imaginary)
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Gregorian date Sunday, December 31, 1 BC."
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(let* ((approx (/ (+ date 2) 366)) ; approximation from below
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(year ; search forward from the approximation
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(+ approx
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(calendar-sum y approx
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(>= date (calendar-julian-to-absolute
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(list 1 1 (1+ y))))
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1)))
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(month ; search forward from January
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(1+ (calendar-sum m 1
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(> date
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(calendar-julian-to-absolute
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(list m
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(if (and (= m 2) (zerop (% year 4)))
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29
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(aref [31 28 31 30 31 30 31
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31 30 31 30 31]
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(1- m)))
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year)))
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1)))
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(day ; calculate the day by subtraction
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(- date (1- (calendar-julian-to-absolute (list month 1 year))))))
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(list month day year)))
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;;;###cal-autoload
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(defun calendar-julian-date-string (&optional date)
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"String of Julian date of Gregorian DATE.
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Defaults to today's date if DATE is not given.
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Driven by the variable `calendar-date-display-form'."
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(calendar-date-string
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(calendar-julian-from-absolute
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(calendar-absolute-from-gregorian (or date (calendar-current-date))))
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nil t))
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;;;###cal-autoload
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(defun calendar-julian-print-date ()
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"Show the Julian calendar equivalent of the date under the cursor."
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(interactive)
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(message "Julian date: %s"
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(calendar-julian-date-string (calendar-cursor-to-date t))))
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;;;###cal-autoload
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(defun calendar-julian-goto-date (date &optional noecho)
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"Move cursor to Julian DATE; echo Julian date unless NOECHO is non-nil."
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(interactive
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(let* ((today (calendar-current-date))
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(year (calendar-read-sexp
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"Julian calendar year (>0)"
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(lambda (x) (> x 0))
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(calendar-extract-year
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(calendar-julian-from-absolute
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(calendar-absolute-from-gregorian
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today)))))
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(month-array calendar-month-name-array)
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(completion-ignore-case t)
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(month (cdr (assoc-string
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(completing-read
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"Julian calendar month name: "
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(mapcar 'list (append month-array nil))
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nil t)
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(calendar-make-alist month-array 1) t)))
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(last
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(if (and (zerop (% year 4)) (= month 2))
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29
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(aref [31 28 31 30 31 30 31 31 30 31 30 31] (1- month))))
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(day (calendar-read-sexp
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"Julian calendar day (%d-%d)"
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(lambda (x)
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(and (< (if (and (= year 1) (= month 1)) 2 0) x)
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(<= x last)))
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nil
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(if (and (= year 1) (= month 1)) 3 1) last)))
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(list (list month day year))))
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(calendar-goto-date (calendar-gregorian-from-absolute
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(calendar-julian-to-absolute date)))
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(or noecho (calendar-julian-print-date)))
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;;;###holiday-autoload
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(defun holiday-julian (month day string)
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"Holiday on MONTH, DAY (Julian) called STRING.
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If MONTH, DAY (Julian) is visible, the value returned is corresponding
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Gregorian date in the form of the list (((month day year) STRING)). Returns
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nil if it is not visible in the current calendar window."
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(let ((gdate (calendar-nongregorian-visible-p
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month day 'calendar-julian-to-absolute
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'calendar-julian-from-absolute
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;; In the Gregorian case, we'd use the lower year when
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;; month >= 11. In the Julian case, there is an offset
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;; of two weeks (ie 1 Nov Greg = 19 Oct Julian). So we
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;; use month >= 10, since it can't cause any problems.
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(lambda (m) (< m 10)))))
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(if gdate (list (list gdate string)))))
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;;;###cal-autoload
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(defun calendar-astro-to-absolute (d)
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"Absolute date of astronomical (Julian) day number D."
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(- d 1721424.5))
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;;;###cal-autoload
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(defun calendar-astro-from-absolute (d)
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"Astronomical (Julian) day number of absolute date D."
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(+ d 1721424.5))
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;;;###cal-autoload
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(defun calendar-astro-date-string (&optional date)
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"String of astronomical (Julian) day number after noon UTC of Gregorian DATE.
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Defaults to today's date if DATE is not given."
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(number-to-string
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(ceiling
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(calendar-astro-from-absolute
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(calendar-absolute-from-gregorian (or date (calendar-current-date)))))))
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;;;###cal-autoload
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(defun calendar-astro-print-day-number ()
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"Show astronomical (Julian) day number after noon UTC on cursor date."
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(interactive)
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(message
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"Astronomical (Julian) day number (at noon UTC): %s.0"
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(calendar-astro-date-string (calendar-cursor-to-date t))))
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;;;###cal-autoload
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(defun calendar-astro-goto-day-number (daynumber &optional noecho)
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"Move cursor to astronomical (Julian) DAYNUMBER.
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Echo astronomical (Julian) day number unless NOECHO is non-nil."
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(interactive (list (calendar-read-sexp
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"Astronomical (Julian) day number (>1721425)"
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(lambda (x) (> x 1721425)))))
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(calendar-goto-date
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(calendar-gregorian-from-absolute
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(floor
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(calendar-astro-to-absolute daynumber))))
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(or noecho (calendar-astro-print-day-number)))
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;;;###diary-autoload
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(defun diary-julian-date ()
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"Julian calendar equivalent of date diary entry."
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;; This function is designed to be used in sexp diary entries, and
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;; may be present in users' diary files, so suppress the warning
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;; about this prefix-less dynamic variable. It's called from
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;; `diary-list-sexp-entries', which binds the variable.
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(with-suppressed-warnings ((lexical date))
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(defvar date))
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(format "Julian date: %s" (calendar-julian-date-string date)))
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;; To be called from diary-list-sexp-entries, where DATE is bound.
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;;;###diary-autoload
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(defun diary-astro-day-number ()
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"Astronomical (Julian) day number diary entry."
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;; This function is designed to be used in sexp diary entries, and
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;; may be present in users' diary files, so suppress the warning
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;; about this prefix-less dynamic variable. It's called from
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;; `diary-list-sexp-entries', which binds the variable.
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(with-suppressed-warnings ((lexical date))
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(defvar date))
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(format "Astronomical (Julian) day number at noon UTC: %s.0"
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(calendar-astro-date-string date)))
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(provide 'cal-julian)
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;;; cal-julian.el ends here
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