(require 'calendar)
(require 'cal-persia)
+(defcustom calendar-dst-check-each-year-flag t
+ "Non-nil means to check each year for DST transitions as needed.
+nil means to assume the next two transitions found after the
+current date apply to all years. This is faster, but not always
+correct, since the dates of Daylight Saving transitions sometimes
+change."
+ :type 'boolean
+ :version "22.1"
+ :group 'calendar)
+
(defvar calendar-current-time-zone-cache nil
"Cache for result of calendar-current-time-zone.")
(cdr candidate-rules)))
(car candidate-rules)))
+;; TODO it might be better to extract this information directly from
+;; the system timezone database. But cross-platform...?
+;; See thread
+;; http://lists.gnu.org/archive/html/emacs-pretest-bug/2006-11/msg00060.html
+(defun calendar-dst-find-data (&optional time)
+ "Find data on the first Daylight Saving Time transitions after TIME.
+TIME defaults to `current-time'. Return value is as described
+for `calendar-current-time-zone'."
+ (let* ((t0 (or time (current-time)))
+ (t0-zone (current-time-zone t0))
+ (t0-utc-diff (car t0-zone))
+ (t0-name (car (cdr t0-zone))))
+ (if (not t0-utc-diff)
+ ;; Little or no time zone information is available.
+ (list nil nil t0-name t0-name nil nil nil nil)
+ (let* ((t1 (calendar-next-time-zone-transition t0))
+ (t2 (and t1 (calendar-next-time-zone-transition t1))))
+ (if (not t2)
+ ;; This locale does not have daylight savings time.
+ (list (/ t0-utc-diff 60) 0 t0-name t0-name nil nil 0 0)
+ ;; Use heuristics to find daylight savings parameters.
+ (let* ((t1-zone (current-time-zone t1))
+ (t1-utc-diff (car t1-zone))
+ (t1-name (car (cdr t1-zone)))
+ (t1-date-sec (calendar-absolute-from-time t1 t0-utc-diff))
+ (t2-date-sec (calendar-absolute-from-time t2 t1-utc-diff))
+ ;; TODO When calendar-dst-check-each-year-flag is non-nil,
+ ;; the rules can be simpler than they currently are.
+ (t1-rules (calendar-time-zone-daylight-rules
+ (car t1-date-sec) t0-utc-diff))
+ (t2-rules (calendar-time-zone-daylight-rules
+ (car t2-date-sec) t1-utc-diff))
+ (t1-time (/ (cdr t1-date-sec) 60))
+ (t2-time (/ (cdr t2-date-sec) 60)))
+ (cons
+ (/ (min t0-utc-diff t1-utc-diff) 60)
+ (cons
+ (/ (abs (- t0-utc-diff t1-utc-diff)) 60)
+ (if (< t0-utc-diff t1-utc-diff)
+ (list t0-name t1-name t1-rules t2-rules t1-time t2-time)
+ (list t1-name t0-name t2-rules t1-rules t2-time t1-time)
+ )))))))))
+
+(defvar calendar-dst-transition-cache nil
+ "Internal cal-dst variable storing date of Daylight Saving Time transitions.
+Value is a list with elements of the form (YEAR START END), where
+START and END are expressions that when evaluated return the
+start and end dates (respectively) for DST in YEAR. Used by the
+function `calendar-dst-find-startend'.")
+
+(defun calendar-dst-find-startend (year)
+ "Find the dates in YEAR on which Daylight Saving Time starts and ends.
+Returns a list (YEAR START END), where START and END are
+expressions that when evaluated return the start and end dates,
+respectively. This function first attempts to use pre-calculated
+data from `calendar-dst-transition-cache', otherwise it calls
+`calendar-dst-find-data' (and adds the results to the cache)."
+ (let ((e (assoc year calendar-dst-transition-cache))
+ f)
+ (or e
+ (progn
+ (setq e (calendar-dst-find-data (encode-time 1 0 0 1 1 year))
+ f (nth 4 e)
+ e (list year f (nth 5 e))
+ calendar-dst-transition-cache
+ (append calendar-dst-transition-cache (list e)))
+ e))))
+
(defun calendar-current-time-zone ()
"Return UTC difference, dst offset, names and rules for current time zone.
Some operating systems cannot provide all this information to Emacs; in this
case, `calendar-current-time-zone' returns a list containing nil for the data
it can't find."
- (or
- calendar-current-time-zone-cache
- (setq
- calendar-current-time-zone-cache
- (let* ((t0 (current-time))
- (t0-zone (current-time-zone t0))
- (t0-utc-diff (car t0-zone))
- (t0-name (car (cdr t0-zone))))
- (if (not t0-utc-diff)
- ;; Little or no time zone information is available.
- (list nil nil t0-name t0-name nil nil nil nil)
- (let* ((t1 (calendar-next-time-zone-transition t0))
- (t2 (and t1 (calendar-next-time-zone-transition t1))))
- (if (not t2)
- ;; This locale does not have daylight savings time.
- (list (/ t0-utc-diff 60) 0 t0-name t0-name nil nil 0 0)
- ;; Use heuristics to find daylight savings parameters.
- (let* ((t1-zone (current-time-zone t1))
- (t1-utc-diff (car t1-zone))
- (t1-name (car (cdr t1-zone)))
- (t1-date-sec (calendar-absolute-from-time t1 t0-utc-diff))
- (t2-date-sec (calendar-absolute-from-time t2 t1-utc-diff))
- (t1-rules (calendar-time-zone-daylight-rules
- (car t1-date-sec) t0-utc-diff))
- (t2-rules (calendar-time-zone-daylight-rules
- (car t2-date-sec) t1-utc-diff))
- (t1-time (/ (cdr t1-date-sec) 60))
- (t2-time (/ (cdr t2-date-sec) 60)))
- (cons
- (/ (min t0-utc-diff t1-utc-diff) 60)
- (cons
- (/ (abs (- t0-utc-diff t1-utc-diff)) 60)
- (if (< t0-utc-diff t1-utc-diff)
- (list t0-name t1-name t1-rules t2-rules t1-time t2-time)
- (list t1-name t0-name t2-rules t1-rules t2-time t1-time)
- )))))))))))
+ (unless calendar-current-time-zone-cache
+ (setq calendar-current-time-zone-cache (calendar-dst-find-data))))
;;; The following eight defvars relating to daylight savings time should NOT be
;;; marked to go into loaddefs.el where they would be evaluated when Emacs is
"*Abbreviated name of daylight-savings time zone at `calendar-location-name'.
For example, \"EDT\" in New York City, \"PDT\" for Los Angeles.")
+
+(defun calendar-dst-starts (year)
+ "Return the date of YEAR on which Daylight Saving Time starts.
+This function respects the value of `calendar-dst-check-each-year-flag'."
+ (or (let ((expr (if calendar-dst-check-each-year-flag
+ (cadr (calendar-dst-find-startend year))
+ (nth 4 calendar-current-time-zone-cache))))
+ (if expr (eval expr)))
+ (and (not (zerop calendar-daylight-time-offset))
+ (calendar-nth-named-day 1 0 4 year))))
+
+(defun calendar-dst-ends (year)
+ "Return the date of YEAR on which Daylight Saving Time ends.
+This function respects the value of `calendar-dst-check-each-year-flag'."
+ (or (let ((expr (if calendar-dst-check-each-year-flag
+ (nth 2 (calendar-dst-find-startend year))
+ (nth 5 calendar-current-time-zone-cache))))
+ (if expr (eval expr)))
+ (and (not (zerop calendar-daylight-time-offset))
+ (calendar-nth-named-day -1 0 10 year))))
+
+
;;;###autoload
(put 'calendar-daylight-savings-starts 'risky-local-variable t)
(defvar calendar-daylight-savings-starts
- (or (car (nthcdr 4 calendar-current-time-zone-cache))
- (and (not (zerop calendar-daylight-time-offset))
- '(calendar-nth-named-day 1 0 4 year)))
+ '(calendar-dst-starts year)
"*Sexp giving the date on which daylight savings time starts.
This is an expression in the variable `year' whose value gives the Gregorian
date in the form (month day year) on which daylight savings time starts. It is
;;;###autoload
(put 'calendar-daylight-savings-ends 'risky-local-variable t)
(defvar calendar-daylight-savings-ends
- (or (car (nthcdr 5 calendar-current-time-zone-cache))
- (and (not (zerop calendar-daylight-time-offset))
- '(calendar-nth-named-day -1 0 10 year)))
+ '(calendar-dst-ends year)
"*Sexp giving the date on which daylight savings time ends.
This is an expression in the variable `year' whose value gives the Gregorian
date in the form (month day year) on which daylight savings time ends. It is