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;;; cal-coptic.el --- calendar functions for the Coptic/Ethiopic calendars -*- lexical-binding: t; -*-
;; Copyright (C) 1995, 1997, 2001-2025 Free Software Foundation, Inc.
;; Author: Edward M. Reingold <reingold@cs.uiuc.edu>
;; Maintainer: emacs-devel@gnu.org
;; Keywords: calendar
;; Human-Keywords: Coptic calendar, Ethiopic calendar, calendar, diary
;; Package: calendar
;; This file is part of GNU Emacs.
;; GNU Emacs 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.
;; GNU Emacs 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 GNU Emacs. If not, see <https://www.gnu.org/licenses/>.
;;; Commentary:
;; See calendar.el.
;;; Code:
(require 'calendar)
;; Not constants because they get let-bound.
(defvar calendar-coptic-month-name-array
["Tut" "Babah" "Hatur" "Kiyahk" "Tubah" "Amshir" "Baramhat" "Barmundah"
"Bashans" "Baunah" "Abib" "Misra" "al-Nasi"]
"Array of the month names in the Coptic calendar.")
(eval-and-compile
(autoload 'calendar-julian-to-absolute "cal-julian"))
(defvar calendar-coptic-epoch
(eval-when-compile (calendar-julian-to-absolute '(8 29 284)))
"Absolute date of start of Coptic calendar = August 29, 284 AD (Julian).")
(defvar calendar-coptic-name "Coptic"
"Used in some message strings.")
(defun calendar-coptic-leap-year-p (year)
"True if YEAR is a leap year on the Coptic calendar."
(zerop (mod (1+ year) 4)))
(defun calendar-coptic-last-day-of-month (month year)
"Return last day of MONTH, YEAR on the Coptic calendar.
The 13th month is not really a month, but the 5 (6 in leap years) day period of
Nisi (Kebus) at the end of the year."
(if (< month 13)
30
(if (calendar-coptic-leap-year-p year)
6
5)))
(defun calendar-coptic-to-absolute (date)
"Compute absolute date from Coptic date DATE.
The absolute date is the number of days elapsed since the (imaginary)
Gregorian date Sunday, December 31, 1 BC."
(let ((month (calendar-extract-month date))
(day (calendar-extract-day date))
(year (calendar-extract-year date)))
(+ (1- calendar-coptic-epoch) ; days before start of calendar
(* 365 (1- year)) ; days in prior years
(/ year 4) ; leap days in prior years
(* 30 (1- month)) ; days in prior months this year
day))) ; days so far this month
(defun calendar-coptic-from-absolute (date)
"Compute the Coptic equivalent for absolute date DATE.
The result is a list of the form (MONTH DAY YEAR).
The absolute date is the number of days elapsed since the imaginary
Gregorian date Sunday, December 31, 1 BC."
(if (< date calendar-coptic-epoch)
(list 0 0 0) ; pre-Coptic date
(let* ((approx (/ (- date calendar-coptic-epoch)
366)) ; approximation from below
(year ; search forward from the approximation
(+ approx
(calendar-sum y approx
(>= date (calendar-coptic-to-absolute
(list 1 1 (1+ y))))
1)))
(month ; search forward from Tot
(1+ (calendar-sum m 1
(> date
(calendar-coptic-to-absolute
(list m
(calendar-coptic-last-day-of-month m
year)
year)))
1)))
(day ; calculate the day by subtraction
(- date
(1- (calendar-coptic-to-absolute (list month 1 year))))))
(list month day year))))
;;;###cal-autoload
(defun calendar-coptic-date-string (&optional date)
"String of Coptic date of Gregorian DATE.
Returns the empty string if DATE is pre-Coptic calendar.
Defaults to today's date if DATE is not given."
(let* ((coptic-date (calendar-coptic-from-absolute
(calendar-absolute-from-gregorian
(or date (calendar-current-date)))))
(y (calendar-extract-year coptic-date))
(m (calendar-extract-month coptic-date)))
(if (< y 1)
""
(calendar-dlet
((monthname (aref calendar-coptic-month-name-array (1- m)))
(day (number-to-string (calendar-extract-day coptic-date)))
(dayname nil)
(month (number-to-string m))
(year (number-to-string y)))
(mapconcat #'eval calendar-date-display-form "")))))
;;;###cal-autoload
(defun calendar-coptic-print-date ()
"Show the Coptic calendar equivalent of the selected date."
(interactive)
(let ((f (calendar-coptic-date-string (calendar-cursor-to-date t))))
(if (string-equal f "")
(message "Date is pre-%s calendar" calendar-coptic-name)
(message "%s date: %s" calendar-coptic-name f))))
(defun calendar-coptic-read-date ()
"Interactively read the arguments for a Coptic date command.
Reads a year, month, and day."
(let* ((today (calendar-current-date))
(year (calendar-read-sexp
"%s calendar year (>0)"
(lambda (x) (> x 0))
(calendar-extract-year
(calendar-coptic-from-absolute
(calendar-absolute-from-gregorian today)))
calendar-coptic-name))
(completion-ignore-case t)
(month (cdr (assoc-string
(completing-read
(format "%s calendar month name: " calendar-coptic-name)
(mapcar 'list
(append calendar-coptic-month-name-array nil))
nil t)
(calendar-make-alist calendar-coptic-month-name-array
1)
t)))
(last (calendar-coptic-last-day-of-month month year))
(day (calendar-read-sexp
"%s calendar day (1-%d)"
(lambda (x) (and (< 0 x) (<= x last)))
nil
calendar-coptic-name last)))
(list (list month day year))))
;;;###cal-autoload
(defun calendar-coptic-goto-date (date &optional noecho)
"Move cursor to Coptic date DATE.
Echo Coptic date unless NOECHO is t."
(interactive (calendar-coptic-read-date))
(calendar-goto-date (calendar-gregorian-from-absolute
(calendar-coptic-to-absolute date)))
(or noecho (calendar-coptic-print-date)))
;; The function below is designed to be used in sexp diary entries,
;; and may be present in users' diary files, so suppress the warning
;; about this prefix-less dynamic variable. It's called from
;; `diary-list-sexp-entries', which binds the variable.
(with-suppressed-warnings ((lexical date))
(defvar date))
;;;###diary-autoload
(defun diary-coptic-date ()
"Coptic calendar equivalent of date diary entry."
(let ((f (calendar-coptic-date-string date)))
(if (string-equal f "")
(format "Date is pre-%s calendar" calendar-coptic-name)
(format "%s date: %s" calendar-coptic-name f))))
(defconst calendar-ethiopic-month-name-array
["Maskaram" "Teqemt" "Khedar" "Takhsas" "Ter" "Yakatit" "Magabit" "Miyazya"
"Genbot" "Sane" "Hamle" "Nahas" "Paguem"]
"Array of the month names in the Ethiopic calendar.")
(defconst calendar-ethiopic-epoch 2796
"Absolute date of start of Ethiopic calendar = August 29, 8 C.E. (Julian).")
(defconst calendar-ethiopic-name "Ethiopic"
"Used in some message strings.")
(defun calendar-ethiopic-to-absolute (thedate)
"Compute absolute date from Ethiopic date DATE.
The absolute date is the number of days elapsed since the (imaginary)
Gregorian date Sunday, December 31, 1 BC."
(let ((calendar-coptic-epoch calendar-ethiopic-epoch))
(calendar-coptic-to-absolute thedate)))
(defun calendar-ethiopic-from-absolute (thedate)
"Compute the Ethiopic equivalent for absolute date DATE.
The result is a list of the form (MONTH DAY YEAR).
The absolute date is the number of days elapsed since the imaginary
Gregorian date Sunday, December 31, 1 BC."
(let ((calendar-coptic-epoch calendar-ethiopic-epoch))
(calendar-coptic-from-absolute thedate)))
;;;###cal-autoload
(defun calendar-ethiopic-date-string (&optional thedate)
"String of Ethiopic date of Gregorian DATE.
Returns the empty string if DATE is pre-Ethiopic calendar.
Defaults to today's date if DATE is not given."
(let ((calendar-coptic-epoch calendar-ethiopic-epoch)
(calendar-coptic-name calendar-ethiopic-name)
(calendar-coptic-month-name-array calendar-ethiopic-month-name-array))
(calendar-coptic-date-string thedate)))
;;;###cal-autoload
(defun calendar-ethiopic-print-date ()
"Show the Ethiopic calendar equivalent of the selected date."
(interactive)
(let ((calendar-coptic-epoch calendar-ethiopic-epoch)
(calendar-coptic-name calendar-ethiopic-name)
(calendar-coptic-month-name-array calendar-ethiopic-month-name-array))
(call-interactively 'calendar-coptic-print-date)))
;;;###cal-autoload
(defun calendar-ethiopic-goto-date (thedate &optional noecho)
"Move cursor to Ethiopic date THEDATE.
Echo Ethiopic date unless NOECHO is t."
(interactive
(let ((calendar-coptic-epoch calendar-ethiopic-epoch)
(calendar-coptic-name calendar-ethiopic-name)
(calendar-coptic-month-name-array calendar-ethiopic-month-name-array))
(calendar-coptic-read-date)))
(calendar-goto-date (calendar-gregorian-from-absolute
(calendar-ethiopic-to-absolute thedate)))
(or noecho (calendar-ethiopic-print-date)))
;; To be called from diary-list-sexp-entries, where DATE is bound.
;;;###diary-autoload
(defun diary-ethiopic-date ()
"Ethiopic calendar equivalent of date diary entry."
(let ((calendar-coptic-epoch calendar-ethiopic-epoch)
(calendar-coptic-name calendar-ethiopic-name)
(calendar-coptic-month-name-array calendar-ethiopic-month-name-array))
(diary-coptic-date)))
(provide 'cal-coptic)
;;; cal-coptic.el ends here
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