1;;; cal-coptic.el --- calendar functions for the Coptic/Ethiopic calendars
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: Coptic calendar, Ethiopic 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 Coptic and Ethiopic calendars.
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 'cal-julian)
42
43(defvar coptic-calendar-month-name-array
44  ["Tut" "Babah" "Hatur" "Kiyahk" "Tubah" "Amshir" "Baramhat" "Barmundah"
45   "Bashans" "Baunah" "Abib" "Misra" "al-Nasi"])
46
47(defvar coptic-calendar-epoch (calendar-absolute-from-julian '(8 29 284))
48  "Absolute date of start of Coptic calendar = August 29, 284 A.D. (Julian).")
49
50(defvar coptic-name "Coptic")
51
52(defun coptic-calendar-leap-year-p (year)
53  "True if YEAR is a leap year on the Coptic calendar."
54  (zerop (mod (1+ year) 4)))
55
56(defun coptic-calendar-last-day-of-month (month year)
57  "Return last day of MONTH, YEAR on the Coptic calendar.
58The 13th month is not really a month, but the 5 (6 in leap years) day period of
59Nisi (Kebus)  at the end of the year."
60  (if (< month 13)
61      30
62    (if (coptic-calendar-leap-year-p year)
63        6
64      5)))
65
66(defun calendar-absolute-from-coptic (date)
67  "Compute absolute date from Coptic date DATE.
68The absolute date is the number of days elapsed since the (imaginary)
69Gregorian date Sunday, December 31, 1 BC."
70  (let ((month (extract-calendar-month date))
71        (day (extract-calendar-day date))
72        (year (extract-calendar-year date)))
73    (+ (1- coptic-calendar-epoch);; Days before start of calendar
74       (* 365 (1- year))         ;; Days in prior years
75       (/ year 4)                ;; Leap days in prior years
76       (* 30 (1- month))         ;; Days in prior months this year
77       day)))                    ;; Days so far this month
78
79
80(defun calendar-coptic-from-absolute (date)
81  "Compute the Coptic equivalent for absolute date DATE.
82The result is a list of the form (MONTH DAY YEAR).
83The absolute date is the number of days elapsed since the imaginary
84Gregorian date Sunday, December 31, 1 BC."
85  (if (< date coptic-calendar-epoch)
86      (list 0 0 0);; pre-Coptic date
87    (let* ((approx (/ (- date coptic-calendar-epoch)
88                      366))   ;; Approximation from below.
89           (year              ;; Search forward from the approximation.
90            (+ approx
91               (calendar-sum y approx
92                 (>= date (calendar-absolute-from-coptic (list 1 1 (1+ y))))
93                 1)))
94           (month             ;; Search forward from Tot.
95            (1+ (calendar-sum m 1
96                  (> date
97                     (calendar-absolute-from-coptic
98                      (list m
99                            (coptic-calendar-last-day-of-month m year)
100                            year)))
101                  1)))
102           (day                ;; Calculate the day by subtraction.
103            (- date
104               (1- (calendar-absolute-from-coptic (list month 1 year))))))
105    (list month day year))))
106
107(defun calendar-coptic-date-string (&optional date)
108  "String of Coptic date of Gregorian DATE.
109Returns the empty string if DATE is pre-Coptic calendar.
110Defaults to today's date if DATE is not given."
111  (let* ((coptic-date (calendar-coptic-from-absolute
112                       (calendar-absolute-from-gregorian
113                        (or date (calendar-current-date)))))
114         (y (extract-calendar-year coptic-date))
115         (m (extract-calendar-month coptic-date)))
116    (if (< y 1)
117        ""
118      (let ((monthname (aref coptic-calendar-month-name-array (1- m)))
119            (day (int-to-string (extract-calendar-day coptic-date)))
120            (dayname nil)
121            (month (int-to-string m))
122            (year (int-to-string y)))
123        (mapconcat 'eval calendar-date-display-form "")))))
124
125(defun calendar-print-coptic-date ()
126  "Show the Coptic calendar equivalent of the selected date."
127  (interactive)
128  (let ((f (calendar-coptic-date-string (calendar-cursor-to-date t))))
129    (if (string-equal f "")
130        (message "Date is pre-%s calendar" coptic-name)
131      (message "%s date: %s" coptic-name f))))
132
133(defun calendar-goto-coptic-date (date &optional noecho)
134  "Move cursor to Coptic date DATE.
135Echo Coptic date unless NOECHO is t."
136  (interactive (coptic-prompt-for-date))
137  (calendar-goto-date (calendar-gregorian-from-absolute
138                       (calendar-absolute-from-coptic date)))
139  (or noecho (calendar-print-coptic-date)))
140
141(defun coptic-prompt-for-date ()
142  "Ask for a Coptic date."
143  (let* ((today (calendar-current-date))
144         (year (calendar-read
145                (format "%s calendar year (>0): " coptic-name)
146                '(lambda (x) (> x 0))
147                (int-to-string
148                 (extract-calendar-year
149                  (calendar-coptic-from-absolute
150                   (calendar-absolute-from-gregorian today))))))
151         (completion-ignore-case t)
152         (month (cdr (assoc-string
153                      (completing-read
154                       (format "%s calendar month name: " coptic-name)
155                       (mapcar 'list
156                               (append coptic-calendar-month-name-array nil))
157                       nil t)
158                      (calendar-make-alist coptic-calendar-month-name-array
159                                           1) t)))
160         (last (coptic-calendar-last-day-of-month month year))
161         (day (calendar-read
162               (format "%s calendar day (1-%d): " coptic-name last)
163               '(lambda (x) (and (< 0 x) (<= x last))))))
164    (list (list month day year))))
165
166(defun diary-coptic-date ()
167  "Coptic calendar equivalent of date diary entry."
168  (let ((f (calendar-coptic-date-string date)))
169    (if (string-equal f "")
170        (format "Date is pre-%s calendar" coptic-name)
171      (format "%s date: %s" coptic-name f))))
172
173(defconst ethiopic-calendar-month-name-array
174  ["Maskaram" "Teqemt" "Khedar" "Takhsas" "Ter" "Yakatit" "Magabit" "Miyazya"
175   "Genbot" "Sane" "Hamle" "Nahas" "Paguem"])
176
177(defconst ethiopic-calendar-epoch 2796
178  "Absolute date of start of Ethiopic calendar = August 29, 8 C.E. (Julian).")
179
180(defconst ethiopic-name "Ethiopic")
181
182(defun calendar-absolute-from-ethiopic (date)
183  "Compute absolute date from Ethiopic date DATE.
184The absolute date is the number of days elapsed since the (imaginary)
185Gregorian date Sunday, December 31, 1 BC."
186  (let ((coptic-calendar-epoch ethiopic-calendar-epoch))
187    (calendar-absolute-from-coptic date)))
188
189(defun calendar-ethiopic-from-absolute (date)
190  "Compute the Ethiopic equivalent for absolute date DATE.
191The result is a list of the form (MONTH DAY YEAR).
192The absolute date is the number of days elapsed since the imaginary
193Gregorian date Sunday, December 31, 1 BC."
194  (let ((coptic-calendar-epoch ethiopic-calendar-epoch))
195    (calendar-coptic-from-absolute date)))
196
197(defun calendar-ethiopic-date-string (&optional date)
198  "String of Ethiopic date of Gregorian DATE.
199Returns the empty string if DATE is pre-Ethiopic calendar.
200Defaults to today's date if DATE is not given."
201  (let ((coptic-calendar-epoch ethiopic-calendar-epoch)
202        (coptic-name ethiopic-name)
203        (coptic-calendar-month-name-array ethiopic-calendar-month-name-array))
204    (calendar-coptic-date-string date)))
205
206(defun calendar-print-ethiopic-date ()
207  "Show the Ethiopic calendar equivalent of the selected date."
208  (interactive)
209  (let ((coptic-calendar-epoch ethiopic-calendar-epoch)
210        (coptic-name ethiopic-name)
211        (coptic-calendar-month-name-array ethiopic-calendar-month-name-array))
212    (call-interactively 'calendar-print-coptic-date)))
213
214(defun calendar-goto-ethiopic-date (date &optional noecho)
215  "Move cursor to Ethiopic date DATE.
216Echo Ethiopic date unless NOECHO is t."
217  (interactive
218   (let ((coptic-calendar-epoch ethiopic-calendar-epoch)
219         (coptic-name ethiopic-name)
220         (coptic-calendar-month-name-array ethiopic-calendar-month-name-array))
221     (coptic-prompt-for-date)))
222  (calendar-goto-date (calendar-gregorian-from-absolute
223                       (calendar-absolute-from-ethiopic date)))
224  (or noecho (calendar-print-ethiopic-date)))
225
226(defun diary-ethiopic-date ()
227  "Ethiopic calendar equivalent of date diary entry."
228  (let ((coptic-calendar-epoch ethiopic-calendar-epoch)
229        (coptic-name ethiopic-name)
230        (coptic-calendar-month-name-array ethiopic-calendar-month-name-array))
231    (diary-coptic-date)))
232
233(provide 'cal-coptic)
234
235;;; arch-tag: 72d49161-25df-4072-9312-b182cdca7627
236;;; cal-coptic.el ends here
237