aboutsummaryrefslogtreecommitdiffstats
path: root/timezone.scm
blob: 2d35dd718d78f6cc1963f1113c8da1c8ba71a6a2 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
;;;; "timezone.scm" Compute timezones and DST from TZ environment variable.
;;; Copyright (C) 1994, 1996, 1997 Aubrey Jaffer
;
;Permission to copy this software, to modify it, to redistribute it,
;to distribute modified versions, and to use it for any purpose is
;granted, subject to the following restrictions and understandings.
;
;1.  Any copy made of this software must include this copyright notice
;in full.
;
;2.  I have made no warranty or representation that the operation of
;this software will be error-free, and I am under no obligation to
;provide any services, by way of maintenance, update, or otherwise.
;
;3.  In conjunction with products arising from the use of this
;material, there shall be no use of my name in any advertising,
;promotional, or sales literature without prior written consent in
;each case.

;; The C-library support for time in general and time-zones in particular
;; stands as a fine example of how *not* to create interfaces.
;;
;; Functions are not consistently named.  Support for GMT is offered in one
;; direction only; The localtime function returns some timezone data in the
;; structure which it returns, and some data in shared global variables.
;; The structure which localtime returns is overwritten with each
;; invocation.  There is no way to find local time in zones other than GMT
;; and the local timezone.
;;
;; The tzfile(5) format encodes only a single timezone per file.  There is
;; no dispatch on zone names, so multiple copies of a timezone file exist
;; under different names.  The TZ `:' specification is unix filesystem
;; specific.  The tzfile(5) format makes no provision for byte-order
;; differences; It mixes 32-bit integer data with characters; specifying
;; ASCII bytes, it is incompatible with different character sizes.  The
;; binary format makes it impossible to easily inspect a file for
;; corruption.
;;
;; I have corrected most of the failings of the C-library time interface in
;; SLIB while maintaining compatablility.  I wrote support for Linux
;; timezone files because on a system where TZ is not set, there is no
;; other way to reveal this information.  HP-UX appears to have a more
;; sensible arrangement; I invite you to add support for it and other
;; platforms.
;;
;; Writing this was a long, tedious, and unenlightening process.  I hope it
;; is useful.
;;
;; Sat Nov 15 00:15:33 1997  Aubrey Jaffer

(require 'scanf)
(require 'time-core)
(require-if 'compiling 'tzfile)

;;; This definition is here so that READ-TZFILE can verify the
;;; existence of these files before loading tzfile.scm to actually
;;; read them.
(define tzfile:vicinity (make-vicinity
			 (if (file-exists? "/usr/share/zoneinfo/GMT")
			     "/usr/share/zoneinfo/"
			     "/usr/lib/zoneinfo/")))

(define (read-tzfile path)
  (define (existing path) (and (file-exists? path) path))
  (let ((realpath
	 (cond ((not path)
		(or (existing (in-vicinity tzfile:vicinity "localtime"))
		    (existing "/etc/localtime")))
	       ((or (char-alphabetic? (string-ref path 0))
		    (char-numeric? (string-ref path 0)))
		(in-vicinity tzfile:vicinity path))
	       (else path))))
    (or (and (file-exists? realpath)
	     (let ((zone #f))
	       (require 'tzfile)
	       (set! zone (tzfile:read realpath))
	       (and zone (list->vector (cons 'tz:file zone)))))
	(slib:error 'read-tzfile realpath))))

;;; Parse Posix TZ string.

(define (string->transition-day-time str)
  (let ((month 0) (week 0) (day #f) (junk #f))
    (or (case (sscanf str "J%u%s" day junk)
	  ((1) (and (<= 1 day 365)
		    (list #f #f day)))
	  (else #f))
	(case (sscanf str "%u%s" day junk)
	  ((1) (and (<= 0 day 365)
		    (list #f #t day)))
	  (else #f))
	(case (sscanf str "M%u.%u.%u%s" month week day junk)
	  ((3) (and (<= 1 month 12)
		    (<= 1 week 5)
		    (<= 0 day 6)
		    (list month week day)))
	  (else #f)))))

(define (string->transition-time str)
  (let ((date #f) (time "2") (junk #f))
    (and (or (eqv? 2 (sscanf str "%[JM.0-9]/%[:0-9]%s" date time junk))
	     (eqv? 1 (sscanf str "%[JM.0-9]" date junk)))
	 (let ((day (string->transition-day-time date))
	       (tim (string->time-offset time)))
	   (and day tim (append day (list tim)))))))

(define (string->time-offset str)
  (and str (string? str) (positive? (string-length str))
       (let ((hh #f) (mm 0) (ss 0) (junk #f))
	 (and (<= 1 (sscanf (if (memv (string-ref str 0) '(#\+ #\-))
				(substring str 1 (string-length str))
				str)
			    "%u:%u:%u%s" hh mm ss junk)
		  3)
	      hh (<= 0 hh 23) (<= 0 mm 59) (<= 0 ss 59)
	      (* (if (char=? #\- (string-ref str 0)) -1 1)
		 (+ ss (* 60 (+ mm (* hh 60)))))))))

(define (string->time-zone tz)
  (let ((tzname #f) (offset #f) (dtzname #f) (doffset #f)
		    (start-str #f) (end-str #f) (junk #f))
    (define found
      (sscanf
       tz "%[^0-9,+-]%[-:+0-9]%[^0-9,+-]%[-:+0-9],%[JM.0-9/:],%[JM.0-9/:]%s"
       tzname offset dtzname doffset start-str end-str junk))
    (set! offset (string->time-offset offset))
    (set! doffset (string->time-offset doffset))
    (cond
     ((and offset (eqv? 3 found))
      (set! doffset (+ -3600 offset))
      (set! found
	    (+ 1
	       (sscanf
		tz "%[^0-9,+-]%[-:+0-9]%[^0-9,+-],%[JM.0-9/:],%[JM.0-9/:]%s"
		tzname offset dtzname start-str end-str junk)))
      (set! offset (string->time-offset offset))))
    (case found
      ((2) (vector 'tz:fixed tz tzname offset))
      ((4) (vector 'tz:rule tz tzname dtzname offset doffset
		   (list 4 1 0 7200) (list 10 5 0 7200)))
      ((6) (let ((start (string->transition-time start-str))
		 (end   (string->transition-time   end-str)))
	     (and
	      start end
	      (vector 'tz:rule tz tzname dtzname offset doffset start end))))
      (else #f))))
;@
(define (time-zone tz)
  (cond ((vector? tz) tz)
	((or (not tz)
	     (eqv? #\: (string-ref tz 0)))
	 (let ()
	   (require 'tzfile)
	   (read-tzfile (and tz (substring tz 1 (string-length tz))))))
	(else (string->time-zone tz))))