;;;; vixie-time.scm -- parse Vixie-style times
;;; Copyright © 2003 Dale Mellor <dale_mellor@users.sourceforge.net>
;;; Copyright © 2018, 2020 Mathieu Lirzin <mthl@gnu.org>
;;;
;;; This file is part of GNU Mcron.
;;;
;;; GNU Mcron 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 Mcron 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 Mcron. If not, see <http://www.gnu.org/licenses/>.
(define-module (mcron vixie-time)
#:use-module (ice-9 match)
#:use-module (ice-9 regex)
#:use-module (mcron job-specifier)
#:use-module (srfi srfi-1)
#:export (parse-vixie-time))
;; In Vixie-style time specifications three-letter symbols are allowed to stand
;; for the numbers corresponding to months and days of the week. We deal with
;; this by making a textual substitution early on in the processing of the
;; strings.
;;
;; We start by defining, once and for all, a list of cons cells consisting of
;; regexps which will match the symbols - which allow an arbitrary number of
;; other letters to appear after them (so that the user can optionally complete
;; the month and day names; this is an extension of Vixie) - and the value which
;; is to replace the symbol.
;;
;; The procedure then takes a string, and then for each symbol in the
;; parse-symbols list attempts to locate an instance and replace it with an
;; ASCII representation of the value it stands for. The procedure returns the
;; modified string. (Note that each symbol can appear only once, which meets the
;; Vixie specifications technically but still allows silly users to mess things
;; up).
(define parse-symbols
(map (lambda (symbol-cell)
(cons (make-regexp (string-append (car symbol-cell) "[[:alpha:]]*")
regexp/icase)
(cdr symbol-cell)))
'(("jan" . "0") ("feb" . "1") ("mar" . "2") ("apr" . "3")
("may" . "4") ("jun" . "5") ("jul" . "6") ("aug" . "7")
("sep" . "8") ("oct" . "9") ("nov" . "10") ("dec" . "11")
("sun" . "0") ("mon" . "1") ("tue" . "2") ("wed" . "3")
("thu" . "4") ("fri" . "5") ("sat" . "6") )))
(define (vixie-substitute-parse-symbols string)
(for-each (lambda (symbol-cell)
(let ((match (regexp-exec (car symbol-cell) string)))
(if match
(set! string (string-append (match:prefix match)
(cdr symbol-cell)
(match:suffix match))))))
parse-symbols)
string)
;; A Vixie time specification is made up of a space-separated list of elements,
;; and the elements consist of a comma-separated list of subelements. The
;; procedure below takes a string holding a subelement, which should have no
;; spaces or symbols (see above) in it, and returns a list of all values which
;; that subelement indicates. There are five distinct cases which must be dealt
;; with: [1] a single '*' which returns a list of all values; [2] a '*' followed
;; by a step specifier; [3] a range and step specifier; [4] a range; and [5] a
;; single number.
;;
;; To perform the computation required for the '*' cases, we need to pass the
;; limit of the allowable range for this subelement as the third argument. As
;; days of the month start at 1 while all the other time components start at 0,
;; we must pass the base of the range to deal with this case also.
(define parse-vixie-subelement-regexp
(make-regexp "^([[:digit:]]+)(-([[:digit:]]+)(/([[:digit:]]+))?)?$"))
(define (parse-vixie-subelement string base limit)
(if (char=? (string-ref string 0) #\*)
(range base limit (if (> (string-length string) 1)
(string->number (substring string 2)) ;; [2]
1)) ;; [1]
(let ((match (regexp-exec parse-vixie-subelement-regexp string)))
(cond ((not match)
(throw 'mcron-error 9
"Bad Vixie-style time specification."))
((match:substring match 5)
(range (string->number (match:substring match 1))
(+ 1 (string->number (match:substring match 3)))
(string->number (match:substring match 5)))) ;; [3]
((match:substring match 3)
(range (string->number (match:substring match 1))
(+ 1 (string->number (match:substring match 3))))) ;; [4]
(else
(list (string->number (match:substring match 1)))))))) ;; [5]
;; A Vixie element contains the entire specification, without spaces or symbols,
;; of the acceptable values for one of the time components (minutes, hours,
;; days, months, week days). Here we break the comma-separated list into
;; subelements, and process each with the procedure above. The return value is a
;; list of all the valid values of all the subcomponents.
;;
;; The second and third arguments are the base and upper limit on the values
;; that can be accepted for this time element.
;;
;; The effect of the 'apply append' is to merge a list of lists into a single
;; list.
(define (parse-vixie-element string base limit)
(apply append
(map (lambda (sub-element)
(parse-vixie-subelement sub-element base limit))
(string-tokenize string (char-set-complement (char-set #\,))))))
(define (interpolate-weekdays mday-list wday-list month year)
"Given a list of days in the month MDAY-LIST and a list of days in the week
WDAY-LIST, return an augmented list of days in the month with weekdays
accounted for."
(let ((t (localtime 0)))
(set-tm:mday t 1)
(set-tm:mon t month)
(set-tm:year t year)
(let ((first-day (tm:wday (cdr (mktime t)))))
(define (range-wday wday)
(let* ((first (- wday first-day))
(first* (if (negative? first) (+ 7 first) first)))
(range (1+ first*) 32 7)))
(apply append mday-list (map range-wday wday-list)))))
;; Return the number of days in a month. Fix up a tm object for the zero'th day
;; of the next month, rationalize the object and extract the day.
(define (days-in-month month year)
(let ((t (localtime 0))) (set-tm:mday t 0)
(set-tm:mon t (+ month 1))
(set-tm:year t year)
(tm:mday (cdr (mktime t)))))
;; We will be working with a list of time-spec's, one for each element of a time
;; specification (minute, hour, ...). Each time-spec holds three pieces of
;; information: a list of acceptable values for this time component, a procedure
;; to get the component from a tm object, and a procedure to set the component
;; in a tm object.
(define (time-spec:list time-spec) (vector-ref time-spec 0))
(define (time-spec:getter time-spec) (vector-ref time-spec 1))
(define (time-spec:setter time-spec) (vector-ref time-spec 2))
;; This procedure modifies the time tm object by setting the component referred
;; to by the time-spec object to its next acceptable value. If this value is not
;; greater than the original (because we have wrapped around the top of the
;; acceptable values list), then the function returns #t, otherwise it returns
;; #f. Thus, if the return value is true then it will be necessary for the
;; caller to increment the next coarser time component as well.
;;
;; The first part of the let block is a concession to humanity; the procedure is
;; simply unreadable without all of these aliases.
(define (increment-time-component time time-spec)
(let ((time-list (time-spec:list time-spec))
(getter (time-spec:getter time-spec))
(setter (time-spec:setter time-spec))
(find-best-next (@@ (mcron job-specifier) %find-best-next)))
(match (find-best-next (getter time) time-list)
((smallest . closest+)
(let ((infinite (inf? closest+)))
(if infinite
(setter time smallest)
(setter time closest+))
infinite)))))
;; There now follows a set of procedures for adjusting an element of time,
;; i.e. taking it to the next acceptable value. In each case, the head of the
;; time-spec-list is expected to correspond to the component of time in
;; question. If the adjusted value wraps around its allowed range, then the next
;; biggest element of time must be adjusted, and so on.
;; There is no specification allowed for the year component of
;; time. Therefore, if we have to make an adjustment (presumably because a
;; monthly adjustment has wrapped around the top of its range) we can simply
;; go to the next year.
(define (nudge-year! time)
(set-tm:year time (+ (tm:year time) 1)))
;; We nudge the month by finding the next allowable value, and if it wraps
;; around we also nudge the year. The time-spec-list will have time-spec
;; objects for month and weekday.
(define (nudge-month! time time-spec-list)
(and (increment-time-component time (car time-spec-list))
(nudge-year! time)))
;; Try to increment the day component of the time according to the combination
;; of the mday-list and the wday-list. If this wraps around the range, or if
;; this falls outside the current month (31st February, for example), then
;; bump the month, set the day to zero, and recurse on this procedure to find
;; the next day in the new month.
;;
;; The time-spec-list will have time-spec entries for mday, month, and
;; weekday.
(define (nudge-day! time time-spec-list)
(if (or (increment-time-component
time
(vector
(interpolate-weekdays (time-spec:list (car time-spec-list))
(time-spec:list (caddr time-spec-list))
(tm:mon time)
(tm:year time))
tm:mday
set-tm:mday))
(> (tm:mday time) (days-in-month (tm:mon time) (tm:year time))))
(begin
(nudge-month! time (cdr time-spec-list))
(set-tm:mday time 0)
(nudge-day! time time-spec-list))))
;; The hour is bumped to the next accceptable value, and the day is bumped if
;; the hour wraps around.
;;
;; The time-spec-list holds specifications for hour, mday, month and weekday.
(define (nudge-hour! time time-spec-list)
(and (increment-time-component time (car time-spec-list))
(nudge-day! time (cdr time-spec-list))))
;; The minute is bumped to the next accceptable value, and the hour is bumped
;; if the minute wraps around.
;;
;; The time-spec-list holds specifications for minute, hour, day-date, month
;; and weekday.
(define (nudge-min! time time-spec-list)
(and (increment-time-component time (car time-spec-list))
(nudge-hour! time (cdr time-spec-list))))
;; This is a procedure which returns a procedure which computes the next time a
;; command should run after the current time, based on the information in the
;; Vixie-style time specification.
;;
;; We start by computing a list of time-spec objects (described above) for the
;; minute, hour, date, month, year and weekday components of the overall time
;; specification [1]. Special care is taken to produce proper values for
;; fields 2 and 4: according to Vixie specification "If both fields are
;; restricted (ie, aren't *), the command will be run when _either_ field
;; matches the current time." This implies that if one of these fields is *,
;; while the other is not, its value should be '() [0], otherwise
;; interpolate-weekdays below will produce incorrect results.
;; When we create the return procedure, it is this list to
;; which references to a time-spec-list will be bound. It will be used by the
;; returned procedure [3] to compute the next time a function should run. Any
;; 7's in the weekday component of the list (the last one) are folded into 0's
;; (both values represent sunday) [2]. Any 0's in the month-day component of the
;; list are removed (this allows a solitary zero to be used to indicate that
;; jobs should only run on certain days of the _week_) [2.1].
;;
;; The returned procedure itself:-
;;
;; Starts by obtaining the current broken-down time [4], and fixing it to
;; ensure that it is an acceptable value, as follows. Each component from the
;; biggest down is checked for acceptability, and if it is not acceptable it
;; is bumped to the next acceptable value (this may cause higher components to
;; also be bumped if there is range wrap-around) and all the lower components
;; are set to -1 so that it can successfully be bumped up to zero if this is
;; an allowed value. The -1 value will be bumped up subsequently to an allowed
;; value [5].
;;
;; Once it has been asserted that the current time is acceptable, or has been
;; adjusted to one minute before the next acceptable time, the minute
;; component is then bumped to the next acceptable time, which may ripple
;; through the higher components if necessary [6]. We now have the next time
;; the command needs to run.
;;
;; The new time is then converted back into a UNIX time and returned [7].
(define (parse-vixie-time string)
(let ((tokens (string-tokenize (vixie-substitute-parse-symbols string))))
(cond
((> (length tokens) 5)
(throw 'mcron-error 9
"Too many fields in Vixie-style time specification"))
((< (length tokens) 5)
(throw 'mcron-error 9
"Not enough fields in Vixie-style time specification")))
(match (map-in-order
(λ (x)
(vector
(let* ((n (vector-ref x 0))
(tok (list-ref tokens n)))
(cond
((and (= n 4)
(string=? tok "*")
(not (string=?
(list-ref tokens 2) "*")))
'())
((and (= n 2)
(string=? tok "*")
(not (string=?
(list-ref tokens 4) "*")))
'())
(else
(parse-vixie-element
tok
(vector-ref x 1)
(vector-ref x 2))))) ; [0]
(vector-ref x 3)
(vector-ref x 4)))
;; token range-top+1 getter setter
`( #( 0 0 60 ,tm:min ,set-tm:min )
#( 1 0 24 ,tm:hour ,set-tm:hour )
#( 2 1 32 ,tm:mday ,set-tm:mday )
#( 3 0 12 ,tm:mon ,set-tm:mon )
#( 4 0 7 ,tm:wday ,set-tm:wday ))) ;; [1]
((and time-spec-list (min hour day month wday))
(vector-set! wday
0
(map (lambda (time-spec)
(if (eqv? time-spec 7) 0 time-spec))
(vector-ref wday 0))) ;; [2]
(vector-set! day
0
(remove (lambda (d) (eqv? d 0))
(vector-ref day 0))) ;; [2.1]
(λ (current-time) ;; [3]
(let ((time (localtime current-time))) ;; [4]
(unless (member (tm:mon time) (time-spec:list month))
(nudge-month! time (cdddr time-spec-list))
(set-tm:mday time 0))
(when (or (eqv? (tm:mday time) 0)
(not (member (tm:mday time)
(interpolate-weekdays
(time-spec:list day)
(time-spec:list wday)
(tm:mon time)
(tm:year time)))))
(nudge-day! time (cddr time-spec-list))
(set-tm:hour time -1))
(unless (member (tm:hour time)
(time-spec:list hour))
(nudge-hour! time (cdr time-spec-list))
(set-tm:min time -1)) ;; [5]
(set-tm:sec time 0)
(nudge-min! time time-spec-list) ;; [6]
(first (mktime time)))))))) ;; [7]
