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;;; cal-persia.el --- calendar functions for the Persian calendar -*- lexical-binding: t; -*-
;; Copyright (C) 1996-1997, 2001-2025 Free Software Foundation, Inc.
;; Author: Edward M. Reingold <reingold@cs.uiuc.edu>
;; Maintainer: emacs-devel@gnu.org
;; Keywords: calendar
;; Human-Keywords: Persian 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)
(defconst calendar-persian-month-name-array
["Farvardin" "Ordibehest" "Xordad" "Tir" "Mordad" "Sahrivar" "Mehr" "Aban"
"Azar" "Dey" "Bahman" "Esfand"]
"Names of the months in the Persian calendar.")
(eval-and-compile
(autoload 'calendar-julian-to-absolute "cal-julian"))
(defconst calendar-persian-epoch
(eval-when-compile (calendar-julian-to-absolute '(3 19 622)))
"Absolute date of start of Persian calendar = March 19, 622 AD (Julian).")
(defun calendar-persian-leap-year-p (year)
"True if YEAR is a leap year on the Persian calendar."
(< (mod (* (mod (mod (if (<= 0 year)
(+ year 2346) ; no year zero
(+ year 2347))
2820)
768)
683)
2820)
683))
(defun calendar-persian-last-day-of-month (month year)
"Return last day of MONTH, YEAR on the Persian calendar."
(cond
((< month 7) 31)
((or (< month 12) (calendar-persian-leap-year-p year)) 30)
(t 29)))
(defun calendar-persian-to-absolute (date)
"Compute absolute date from Persian 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)))
(if (< year 0)
(+ (calendar-persian-to-absolute
(list month day (1+ (mod year 2820))))
(* 1029983 (floor year 2820)))
(+ (1- calendar-persian-epoch) ; days before epoch
(* 365 (1- year)) ; days in prior years
(* 683 ; leap days in prior 2820-year cycles
(floor (+ year 2345) 2820))
(* 186 ; leap days in prior 768 year cycles
(floor (mod (+ year 2345) 2820) 768))
(floor ; leap years in current 768 or 516 year cycle
(* 683 (mod (mod (+ year 2345) 2820) 768))
2820)
-568 ; leap years in Persian years -2345...-1
(calendar-sum ; days in prior months this year
m 1 (< m month)
(calendar-persian-last-day-of-month m year))
day)))) ; days so far this month
(defun calendar-persian-year-from-absolute (date)
"Persian year corresponding to the absolute DATE."
(let* ((d0 ; prior days since start of 2820 cycles
(- date (calendar-persian-to-absolute (list 1 1 -2345))))
(n2820 ; completed 2820-year cycles
(floor d0 1029983))
(d1 ; prior days not in n2820
(mod d0 1029983))
(n768 ; 768-year cycles not in n2820
(floor d1 280506))
(d2 ; prior days not in n2820 or n768
(mod d1 280506))
(n1 ; years not in n2820 or n768
(floor (* 2820 (+ d2 366)) 1029983))
(year (+ (* 2820 n2820) ; complete 2820 year cycles
(* 768 n768) ; complete 768 year cycles
;; Remaining years.
(if (= d1 1029617) ; last day of 2820 year cycle
(1- n1)
n1)
-2345))) ; years before year 1
(if (< year 1)
(1- year) ; no year zero
year)))
(defun calendar-persian-from-absolute (date)
"Compute the Persian 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* ((year (calendar-persian-year-from-absolute date))
(month ; search forward from Farvardin
(1+ (calendar-sum m 1
(> date
(calendar-persian-to-absolute
(list
m
(calendar-persian-last-day-of-month m year)
year)))
1)))
(day ; calculate the day by subtraction
(- date (1- (calendar-persian-to-absolute
(list month 1 year))))))
(list month day year)))
;;;###cal-autoload
(defun calendar-persian-date-string (&optional date)
"String of Persian date of Gregorian DATE, default today."
(let* ((persian-date (calendar-persian-from-absolute
(calendar-absolute-from-gregorian
(or date (calendar-current-date)))))
(y (calendar-extract-year persian-date))
(m (calendar-extract-month persian-date)))
(calendar-dlet
((monthname (aref calendar-persian-month-name-array (1- m)))
(day (number-to-string (calendar-extract-day persian-date)))
(year (number-to-string y))
(month (number-to-string m))
dayname)
(mapconcat #'eval calendar-date-display-form ""))))
;;;###cal-autoload
(defun calendar-persian-print-date ()
"Show the Persian calendar equivalent of the selected date."
(interactive)
(message "Persian date: %s"
(calendar-persian-date-string (calendar-cursor-to-date t))))
(defun calendar-persian-read-date ()
"Interactively read the arguments for a Persian date command.
Reads a year, month, and day."
(let* ((year (calendar-read-sexp
"Persian calendar year (not 0)"
(lambda (x) (not (zerop x)))
(calendar-extract-year
(calendar-persian-from-absolute
(calendar-absolute-from-gregorian
(calendar-current-date))))))
(completion-ignore-case t)
(month (cdr (assoc
(completing-read
"Persian calendar month name: "
(mapcar 'list
(append calendar-persian-month-name-array nil))
nil t)
(calendar-make-alist calendar-persian-month-name-array
1))))
(last (calendar-persian-last-day-of-month month year))
(day (calendar-read-sexp
"Persian calendar day (1-%d)"
(lambda (x) (and (< 0 x) (<= x last)))
nil
last)))
(list (list month day year))))
;;;###cal-autoload
(defun calendar-persian-goto-date (date &optional noecho)
"Move cursor to Persian date DATE.
Echo Persian date unless NOECHO is non-nil."
(interactive (calendar-persian-read-date))
(calendar-goto-date (calendar-gregorian-from-absolute
(calendar-persian-to-absolute date)))
(or noecho (calendar-persian-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-persian-date ()
"Persian calendar equivalent of date diary entry."
(format "Persian date: %s" (calendar-persian-date-string date)))
(provide 'cal-persia)
;;; cal-persia.el ends here
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