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;;; cal-coptic.el --- calendar functions for the Coptic/Ethiopic calendars
;; Copyright (C) 1995, 1997 Free Software Foundation, Inc.
;; Author: Edward M. Reingold <reingold@cs.uiuc.edu>
;; Keywords: calendar
;; Human-Keywords: Coptic calendar, Ethiopic calendar, calendar, diary
;; 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 2, 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; see the file COPYING. If not, write to the
;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
;; Boston, MA 02111-1307, USA.
;;; Commentary:
;; This collection of functions implements the features of calendar.el and
;; diary.el that deal with the Coptic and Ethiopic calendars.
;; Technical details of all the calendrical calculations can be found in
;; ``Calendrical Calculations'' by Nachum Dershowitz and Edward M. Reingold,
;; Cambridge University Press (1997).
;; Comments, corrections, and improvements should be sent to
;; Edward M. Reingold Department of Computer Science
;; (217) 333-6733 University of Illinois at Urbana-Champaign
;; reingold@cs.uiuc.edu 1304 West Springfield Avenue
;; Urbana, Illinois 61801
;;; Code:
(require 'cal-julian)
(defvar coptic-calendar-month-name-array
["Tut" "Babah" "Hatur" "Kiyahk" "Tubah" "Amshir" "Baramhat" "Barmundah"
"Bashans" "Baunah" "Abib" "Misra" "al-Nasi"])
(defvar coptic-calendar-epoch (calendar-absolute-from-julian '(8 29 284))
"Absolute date of start of Coptic calendar = August 29, 284 A.D. (Julian).")
(defconst coptic-name "Coptic")
(defun coptic-calendar-leap-year-p (year)
"True if YEAR is a leap year on the Coptic calendar."
(zerop (mod (1+ year) 4)))
(defun coptic-calendar-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 (coptic-calendar-leap-year-p year)
6
5)))
(defun calendar-absolute-from-coptic (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 (extract-calendar-month date))
(day (extract-calendar-day date))
(year (extract-calendar-year date)))
(+ (1- coptic-calendar-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 coptic-calendar-epoch)
(list 0 0 0);; pre-Coptic date
(let* ((approx (/ (- date coptic-calendar-epoch)
366)) ;; Approximation from below.
(year ;; Search forward from the approximation.
(+ approx
(calendar-sum y approx
(>= date (calendar-absolute-from-coptic (list 1 1 (1+ y))))
1)))
(month ;; Search forward from Tot.
(1+ (calendar-sum m 1
(> date
(calendar-absolute-from-coptic
(list m
(coptic-calendar-last-day-of-month m year)
year)))
1)))
(day ;; Calculate the day by subtraction.
(- date
(1- (calendar-absolute-from-coptic (list month 1 year))))))
(list month day year))))
(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 (extract-calendar-year coptic-date))
(m (extract-calendar-month coptic-date)))
(if (< y 1)
""
(let ((monthname (aref coptic-calendar-month-name-array (1- m)))
(day (int-to-string (extract-calendar-day coptic-date)))
(dayname nil)
(month (int-to-string m))
(year (int-to-string y)))
(mapconcat 'eval calendar-date-display-form "")))))
(defun calendar-print-coptic-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" coptic-name)
(message "%s date: %s" coptic-name f))))
(defun calendar-goto-coptic-date (date &optional noecho)
"Move cursor to Coptic date DATE.
Echo Coptic date unless NOECHO is t."
(interactive (coptic-prompt-for-date))
(calendar-goto-date (calendar-gregorian-from-absolute
(calendar-absolute-from-coptic date)))
(or noecho (calendar-print-coptic-date)))
(defun coptic-prompt-for-date ()
"Ask for a Coptic date."
(let* ((today (calendar-current-date))
(year (calendar-read
(format "%s calendar year (>0): " coptic-name)
'(lambda (x) (> x 0))
(int-to-string
(extract-calendar-year
(calendar-coptic-from-absolute
(calendar-absolute-from-gregorian today))))))
(completion-ignore-case t)
(month (cdr (assoc-ignore-case
(completing-read
(format "%s calendar month name: " coptic-name)
(mapcar 'list
(append coptic-calendar-month-name-array nil))
nil t)
(calendar-make-alist coptic-calendar-month-name-array
1))))
(last (coptic-calendar-last-day-of-month month year))
(day (calendar-read
(format "%s calendar day (1-%d): " coptic-name last)
'(lambda (x) (and (< 0 x) (<= x last))))))
(list (list month day year))))
(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" coptic-name)
(format "%s date: %s" coptic-name f))))
(defconst ethiopic-calendar-month-name-array
["Maskaram" "Teqemt" "Khedar" "Takhsas" "Ter" "Yakatit" "Magabit" "Miyazya"
"Genbot" "Sane" "Hamle" "Nahas" "Paguem"])
(defconst ethiopic-calendar-epoch 2796
"Absolute date of start of Ethiopic calendar = August 29, 8 C.E. (Julian).")
(defconst ethiopic-name "Ethiopic")
(defun calendar-absolute-from-ethiopic (date)
"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 ((coptic-calendar-epoch ethiopic-calendar-epoch))
(calendar-absolute-from-coptic date)))
(defun calendar-ethiopic-from-absolute (date)
"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 ((coptic-calendar-epoch ethiopic-calendar-epoch))
(calendar-coptic-from-absolute date)))
(defun calendar-ethiopic-date-string (&optional date)
"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 ((coptic-calendar-epoch ethiopic-calendar-epoch)
(coptic-name ethiopic-name)
(coptic-calendar-month-name-array ethiopic-calendar-month-name-array))
(calendar-coptic-date-string date)))
(defun calendar-print-ethiopic-date ()
"Show the Ethiopic calendar equivalent of the selected date."
(interactive)
(let ((coptic-calendar-epoch ethiopic-calendar-epoch)
(coptic-name ethiopic-name)
(coptic-calendar-month-name-array ethiopic-calendar-month-name-array))
(call-interactively 'calendar-print-coptic-date)))
(defun calendar-goto-ethiopic-date (date &optional noecho)
"Move cursor to Ethiopic date DATE.
Echo Ethiopic date unless NOECHO is t."
(interactive
(let ((coptic-calendar-epoch ethiopic-calendar-epoch)
(coptic-name ethiopic-name)
(coptic-calendar-month-name-array ethiopic-calendar-month-name-array))
(coptic-prompt-for-date)))
(calendar-goto-date (calendar-gregorian-from-absolute
(calendar-absolute-from-ethiopic date)))
(or noecho (calendar-print-ethiopic-date)))
(defun diary-ethiopic-date ()
"Ethiopic calendar equivalent of date diary entry."
(let ((coptic-calendar-epoch ethiopic-calendar-epoch)
(coptic-name ethiopic-name)
(coptic-calendar-month-name-array ethiopic-calendar-month-name-array))
(diary-coptic-date)))
(provide 'cal-coptic)
;;; cal-coptic.el ends here
|
