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;;; Timezone package for GNU Emacs
;; Copyright(C) 1990 Masanobu UMEDA (umerin@mse.kyutech.ac.jp)
;; $Header: timezone.el,v 1.1 90/12/11 11:50:10 umerin Exp $
;; this version modified by jwz@lucid.com to do timezone-conversion correctly.

;; This file is part of GNU Emacs.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY.  No author or distributor
;; accepts responsibility to anyone for the consequences of using it
;; or for whether it serves any particular purpose or works at all,
;; unless he says so in writing.  Refer to the GNU Emacs General Public
;; License for full details.

;; Everyone is granted permission to copy, modify and redistribute
;; GNU Emacs, but only under the conditions described in the
;; GNU Emacs General Public License.   A copy of this license is
;; supposed to have been given to you along with GNU Emacs so you
;; can know your rights and responsibilities.  It should be in a
;; file named COPYING.  Among other things, the copyright notice
;; and this notice must be preserved on all copies.

(provide 'timezone)

(defvar timezone-world-timezones
  '(("EET" . -0200) ("MET" . -0100)
    ("GMT" . +0000)
    ("EDT" . +0400) ("EST" . +0500)
    ("CDT" . +0500) ("CST" . +0600)
    ("MDT" . +0600) ("MST" . +0700)
    ("PDT" . +0700) ("PST" . +0800)
    ("JST" . +0900)
    ("GMT+1" . +0100) ("GMT+2" . +0200) ("GMT+3" . +0300)
    ("GMT+4" . +0400) ("GMT+5" . +0500) ("GMT+6" . +0600)
    ("GMT+7" . +0700) ("GMT+8" . +0800) ("GMT+9" . +0900)
    ("GMT+10" . +1000) ("GMT+11" . +1100) ("GMT+12" . +1200) ("GMT+13" . +1300)
    ("GMT-1" . -0100) ("GMT-2" . -0200) ("GMT-3" . -0300)
    ("GMT-4" . -0400) ("GMT-5" . -0500) ("GMT-6" . -0600)
    ("GMT-7" . -0700) ("GMT-8" . -0800) ("GMT-9" . -0900)
    ("GMT-10" . -1000) ("GMT-11" . -1100) ("GMT-12" . -1200))
  "*Time differentials of timezone from GMT in hour.")

(defvar timezone-months-assoc
  '(("JAN" .  1)("FEB" .  2)("MAR" .  3)
    ("APR" .  4)("MAY" .  5)("JUN" .  6)
    ("JUL" .  7)("AUG" .  8)("SEP" .  9)
    ("OCT" . 10)("NOV" . 11)("DEC" . 12))
  "Alist of first three letters of a month and its numerical representation.")

(defun timezone-make-date-arpa-standard (date &optional local timezone)
  "Convert DATE to an arpanet standard date.
Optional 1st argumetn LOCAL specifies the default local timezone of the DATE.
Optional 2nd argument TIMEZONE specifies a timezone to be represented in."
  (let* ((date   (timezone-parse-date date))
	 (year   (string-to-int (aref date 0)))
	 (month  (string-to-int (aref date 1)))
	 (day    (string-to-int (aref date 2)))
	 (time   (timezone-parse-time (aref date 3)))
	 (hour   (string-to-int (aref time 0)))
	 (minute (string-to-int (aref time 1)))
	 (second (string-to-int (aref time 2)))
	 (local  (or (aref date 4) local)) ;Use original if defined
	 (timezone (or timezone local))
	 (diff   (- (timezone-zone-to-hour timezone)
		    (timezone-zone-to-hour local)))
	 (new    (timezone-fix-time year month day
				    (+ hour diff) minute second)))
    (timezone-make-arpa-date (aref new 0) (aref new 1) (aref new 2)
			     (timezone-make-time-string
			      (aref new 3) (aref new 4) (aref new 5))
			     timezone)
    ))

(defun timezone-make-date-sortable (date &optional local timezone)
  "Convert DATE to a sortable date string.
Optional 1st argumetn LOCAL specifies the default local timezone of the DATE.
Optional 2nd argument TIMEZONE specifies a timezone to be represented in."
  (let* ((date   (timezone-parse-date date))
	 (year   (string-to-int (aref date 0)))
	 (month  (string-to-int (aref date 1)))
	 (day    (string-to-int (aref date 2)))
	 (time   (timezone-parse-time (aref date 3)))
	 (hour   (string-to-int (aref time 0)))
	 (minute (string-to-int (aref time 1)))
	 (second (string-to-int (aref time 2)))
	 (local  (or (aref date 4) local)) ;Use original if defined
	 (timezone (or timezone local))
	 ;; ## jwz: the logic was reversed here.
	 (diff   (- (timezone-zone-to-hour local)
		    (timezone-zone-to-hour timezone)))
	 (new    (timezone-fix-time year month day
				    (+ hour diff) minute second)))
    (timezone-make-sortable-date (aref new 0) (aref new 1) (aref new 2)
				 (timezone-make-time-string
				  (aref new 3) (aref new 4) (aref new 5)))
    ))


;;
;; Parsers and Constructors of Date and Time
;;

(defun timezone-make-arpa-date (year month day time &optional timezone)
  "Make arpanet standard date string from YEAR, MONTH, DAY, and TIME.
Optional argument TIMEZONE specifies a time zone."
  (format "%02d %s %02d %s%s"
	  day
	  (capitalize (car (rassq month timezone-months-assoc)))
	  (- year (* (/ year 100) 100))	;1990 -> 90
	  time
	  (if timezone (concat " " timezone) "")
	  ))

(defun timezone-make-sortable-date (year month day time)
  "Make sortable date string from YEAR, MONTH, DAY, and TIME."
  (format "%02d%02d%02d%s"
	  (- year (* (/ year 100) 100))	;1990 -> 90
	  month day time))

(defun timezone-make-time-string (hour minute second)
  "Make time string from HOUR, MINUTE, and SECOND."
  (format "%02d:%02d:%02d" hour minute second))

(defun timezone-parse-date (date)
  "Parse DATE and return a vector [year month day time timezone].
19 is prepended to year if necessary. Timezone may be NIL if nothing.
Understand the following styles:
 (1) 14 Apr 89 03:20[:12] [GMT]
 (2) Fri, 17 Mar 89 4:01[:33] [GMT]
 (3) Mon Jan 16 16:12[:37] [GMT] 1989"
  (let ((date (or date ""))
	(year nil)
	(month nil)
	(day nil)
	(time nil)
	(zone nil))			;This may be nil.
    (cond ((string-match
"\\([0-9]+\\) \\([^ ,]+\\) \\([0-9]+\\) \\([0-9]+:[0-9:]+\\)[ ]*\\'" date)
	   ;; Styles: (1) and (2) without timezone
	   (setq year 3 month 2 day 1 time 4 zone nil))
	  ((string-match
"\\([0-9]+\\) \\([^ ,]+\\) \\([0-9]+\\) \\([0-9]+:[0-9:]+\\)[ ]*\\([-+a-zA-Z0-9]+\\)" date)
	   ;; Styles: (1) and (2) with timezone and buggy timezone
	   (setq year 3 month 2 day 1 time 4 zone 5))
	  ((string-match
"\\([^ ,]+\\) \\([0-9]+\\) \\([0-9]+:[0-9:]+\\) \\([0-9]+\\)" date)
	   ;; Styles: (3) without timezone
	   (setq year 4 month 1 day 2 time 3 zone nil))
	  ((string-match
"\\([^ ,]+\\) \\([0-9]+\\) \\([0-9]+:[0-9:]+\\) \\([-+a-zA-Z0-9]+\\) \\([0-9]+\\)" date)
	   ;; Styles: (3) with timezoen
	   (setq year 5 month 1 day 2 time 3 zone 4)))
    (if year
	(progn
	  (setq year
		(substring date (match-beginning year) (match-end year)))
	  ;; I don't care about 2000 year.  There must come out a
	  ;; better program by then.
	  (if (> (length year) 2)
	      (setq year (substring year -2 nil))) ;Use last two letters
	  (setq month
		(int-to-string
		 (cdr
		  (assoc
		   (upcase
		    (substring date
			       (match-beginning month) (match-end month)))
		   timezone-months-assoc))))
	  (setq day
		(substring date (match-beginning day) (match-end day)))
	  (setq time
		(substring date (match-beginning time) (match-end time)))))
    (if zone
	(setq zone
	      (substring date (match-beginning zone) (match-end zone))))
    ;; Return a vector.
    (if year
	(vector year month day time zone)
      (vector "0" "0" "0" "0" nil))
    ))

(defun timezone-parse-time (time)
  "Parse TIME (HH:MM:SS) and return a vector [hour minute second]."
  (let ((time (or time ""))
	(hour nil)
	(minute nil)
	(second nil))
    (cond ((string-match "\\`\\([0-9]+\\):\\([0-9]+\\):\\([0-9]+\\)\\'" time)
	   ;; HH:MM:SS
	   (setq hour 1 minute 2 second 3))
	  ((string-match "\\`\\([0-9]+\\):\\([0-9]+\\)\\'" time)
	   ;; HH:MM
	   (setq hour 1 minute 2 second nil)))
    ;; Return [hour minute second]
    (vector
     (if hour
	 (substring time (match-beginning hour) (match-end hour)) "0")
     (if minute
	 (substring time (match-beginning minute) (match-end minute)) "0")
     (if second
	 (substring time (match-beginning second) (match-end second)) "0"))
    ))


;; Miscellaneous

(defun timezone-zone-to-hour (timezone)
  "Translate TIMEZONE (in zonename or integer) to integer hour."
  (if timezone
      (progn
	(setq timezone
	      (or (cdr (assoc (upcase timezone) timezone-world-timezones))
		  ;; +0900
		  timezone))
	(if (stringp timezone)
	    (setq timezone (string-to-int timezone)))
	(/ timezone 100))
    0))

(defun timezone-fix-time (year month day hour minute second)
  "Fix date and time."
  (cond ((<= 24 hour)			;24 -> 00
	 (setq hour (- hour 24))
	 (setq day  (1+ day))
	 (if (< (timezone-last-day-of-month month year) day)
	     (progn
	       (setq month (1+ month))
	       (setq day 1)
	       (if (< 12 month)
		   (progn
		     (setq month 1)
		     (setq year (1+ year))
		     ))
	       )))
	((> 0 hour)
	 (setq hour (+ hour 24))
	 (setq day  (1- day))
	 (if (> 1 day)
	     (progn
	       (setq month (1- month))
	       (if (> 1 month)
		   (progn
		     (setq month 12)
		     (setq year (1- year))
		     ))
	       (setq day (timezone-last-day-of-month month year))
	       )))
	)
  (vector year month day hour minute second))

;; Partly copied from Calendar program by Edward M. Reingold.
;; Thanks a lot.

(defun timezone-last-day-of-month (month year)
  "The last day in MONTH during YEAR."
  (if (and (= month 2) (timezone-leap-year-p year))
      29
    (aref [31 28 31 30 31 30 31 31 30 31 30 31] (1- month))))

(defun timezone-leap-year-p (year)
  "Returns t if YEAR is a Gregorian leap year."
  (or (and (zerop  (mod year 4))
	   (not (zerop (mod year 100))))
      (zerop (mod year 400))))