summaryrefslogtreecommitdiff
path: root/absl/time/internal/cctz/src/time_zone_format.cc
blob: 2e02233ce118075915ca18fe28fee216cba28e4e (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
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
// Copyright 2016 Google Inc. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//   https://www.apache.org/licenses/LICENSE-2.0
//
//   Unless required by applicable law or agreed to in writing, software
//   distributed under the License is distributed on an "AS IS" BASIS,
//   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//   See the License for the specific language governing permissions and
//   limitations under the License.

#if !defined(HAS_STRPTIME)
#if !defined(_MSC_VER) && !defined(__MINGW32__)
#define HAS_STRPTIME 1  // assume everyone has strptime() except windows
#endif
#endif

#if defined(HAS_STRPTIME) && HAS_STRPTIME
#if !defined(_XOPEN_SOURCE)
#define _XOPEN_SOURCE  // Definedness suffices for strptime.
#endif
#endif

#include "absl/base/config.h"
#include "absl/time/internal/cctz/include/cctz/time_zone.h"

// Include time.h directly since, by C++ standards, ctime doesn't have to
// declare strptime.
#include <time.h>

#include <cctype>
#include <chrono>
#include <cstddef>
#include <cstdint>
#include <cstring>
#include <ctime>
#include <limits>
#include <string>
#include <vector>
#if !HAS_STRPTIME
#include <iomanip>
#include <sstream>
#endif

#include "absl/time/internal/cctz/include/cctz/civil_time.h"
#include "time_zone_if.h"

namespace absl {
ABSL_NAMESPACE_BEGIN
namespace time_internal {
namespace cctz {
namespace detail {

namespace {

#if !HAS_STRPTIME
// Build a strptime() using C++11's std::get_time().
char* strptime(const char* s, const char* fmt, std::tm* tm) {
  std::istringstream input(s);
  input >> std::get_time(tm, fmt);
  if (input.fail()) return nullptr;
  return const_cast<char*>(s) +
         (input.eof() ? strlen(s) : static_cast<std::size_t>(input.tellg()));
}
#endif

// Convert a cctz::weekday to a tm_wday value (0-6, Sunday = 0).
int ToTmWday(weekday wd) {
  switch (wd) {
    case weekday::sunday:
      return 0;
    case weekday::monday:
      return 1;
    case weekday::tuesday:
      return 2;
    case weekday::wednesday:
      return 3;
    case weekday::thursday:
      return 4;
    case weekday::friday:
      return 5;
    case weekday::saturday:
      return 6;
  }
  return 0; /*NOTREACHED*/
}

// Convert a tm_wday value (0-6, Sunday = 0) to a cctz::weekday.
weekday FromTmWday(int tm_wday) {
  switch (tm_wday) {
    case 0:
      return weekday::sunday;
    case 1:
      return weekday::monday;
    case 2:
      return weekday::tuesday;
    case 3:
      return weekday::wednesday;
    case 4:
      return weekday::thursday;
    case 5:
      return weekday::friday;
    case 6:
      return weekday::saturday;
  }
  return weekday::sunday; /*NOTREACHED*/
}

std::tm ToTM(const time_zone::absolute_lookup& al) {
  std::tm tm{};
  tm.tm_sec = al.cs.second();
  tm.tm_min = al.cs.minute();
  tm.tm_hour = al.cs.hour();
  tm.tm_mday = al.cs.day();
  tm.tm_mon = al.cs.month() - 1;

  // Saturate tm.tm_year is cases of over/underflow.
  if (al.cs.year() < std::numeric_limits<int>::min() + 1900) {
    tm.tm_year = std::numeric_limits<int>::min();
  } else if (al.cs.year() - 1900 > std::numeric_limits<int>::max()) {
    tm.tm_year = std::numeric_limits<int>::max();
  } else {
    tm.tm_year = static_cast<int>(al.cs.year() - 1900);
  }

  tm.tm_wday = ToTmWday(get_weekday(al.cs));
  tm.tm_yday = get_yearday(al.cs) - 1;
  tm.tm_isdst = al.is_dst ? 1 : 0;
  return tm;
}

// Returns the week of the year [0:53] given a civil day and the day on
// which weeks are defined to start.
int ToWeek(const civil_day& cd, weekday week_start) {
  const civil_day d(cd.year() % 400, cd.month(), cd.day());
  return static_cast<int>((d - prev_weekday(civil_year(d), week_start)) / 7);
}

const char kDigits[] = "0123456789";

// Formats a 64-bit integer in the given field width.  Note that it is up
// to the caller of Format64() [and Format02d()/FormatOffset()] to ensure
// that there is sufficient space before ep to hold the conversion.
char* Format64(char* ep, int width, std::int_fast64_t v) {
  bool neg = false;
  if (v < 0) {
    --width;
    neg = true;
    if (v == std::numeric_limits<std::int_fast64_t>::min()) {
      // Avoid negating minimum value.
      std::int_fast64_t last_digit = -(v % 10);
      v /= 10;
      if (last_digit < 0) {
        ++v;
        last_digit += 10;
      }
      --width;
      *--ep = kDigits[last_digit];
    }
    v = -v;
  }
  do {
    --width;
    *--ep = kDigits[v % 10];
  } while (v /= 10);
  while (--width >= 0) *--ep = '0';  // zero pad
  if (neg) *--ep = '-';
  return ep;
}

// Formats [0 .. 99] as %02d.
char* Format02d(char* ep, int v) {
  *--ep = kDigits[v % 10];
  *--ep = kDigits[(v / 10) % 10];
  return ep;
}

// Formats a UTC offset, like +00:00.
char* FormatOffset(char* ep, int offset, const char* mode) {
  // TODO: Follow the RFC3339 "Unknown Local Offset Convention" and
  // generate a "negative zero" when we're formatting a zero offset
  // as the result of a failed load_time_zone().
  char sign = '+';
  if (offset < 0) {
    offset = -offset;  // bounded by 24h so no overflow
    sign = '-';
  }
  const int seconds = offset % 60;
  const int minutes = (offset /= 60) % 60;
  const int hours = offset /= 60;
  const char sep = mode[0];
  const bool ext = (sep != '\0' && mode[1] == '*');
  const bool ccc = (ext && mode[2] == ':');
  if (ext && (!ccc || seconds != 0)) {
    ep = Format02d(ep, seconds);
    *--ep = sep;
  } else {
    // If we're not rendering seconds, sub-minute negative offsets
    // should get a positive sign (e.g., offset=-10s => "+00:00").
    if (hours == 0 && minutes == 0) sign = '+';
  }
  if (!ccc || minutes != 0 || seconds != 0) {
    ep = Format02d(ep, minutes);
    if (sep != '\0') *--ep = sep;
  }
  ep = Format02d(ep, hours);
  *--ep = sign;
  return ep;
}

// Formats a std::tm using strftime(3).
void FormatTM(std::string* out, const std::string& fmt, const std::tm& tm) {
  // strftime(3) returns the number of characters placed in the output
  // array (which may be 0 characters).  It also returns 0 to indicate
  // an error, like the array wasn't large enough.  To accommodate this,
  // the following code grows the buffer size from 2x the format string
  // length up to 32x.
  for (std::size_t i = 2; i != 32; i *= 2) {
    std::size_t buf_size = fmt.size() * i;
    std::vector<char> buf(buf_size);
    if (std::size_t len = strftime(&buf[0], buf_size, fmt.c_str(), &tm)) {
      out->append(&buf[0], len);
      return;
    }
  }
}

// Used for %E#S/%E#f specifiers and for data values in parse().
template <typename T>
const char* ParseInt(const char* dp, int width, T min, T max, T* vp) {
  if (dp != nullptr) {
    const T kmin = std::numeric_limits<T>::min();
    bool erange = false;
    bool neg = false;
    T value = 0;
    if (*dp == '-') {
      neg = true;
      if (width <= 0 || --width != 0) {
        ++dp;
      } else {
        dp = nullptr;  // width was 1
      }
    }
    if (const char* const bp = dp) {
      while (const char* cp = strchr(kDigits, *dp)) {
        int d = static_cast<int>(cp - kDigits);
        if (d >= 10) break;
        if (value < kmin / 10) {
          erange = true;
          break;
        }
        value *= 10;
        if (value < kmin + d) {
          erange = true;
          break;
        }
        value -= d;
        dp += 1;
        if (width > 0 && --width == 0) break;
      }
      if (dp != bp && !erange && (neg || value != kmin)) {
        if (!neg || value != 0) {
          if (!neg) value = -value;  // make positive
          if (min <= value && value <= max) {
            *vp = value;
          } else {
            dp = nullptr;
          }
        } else {
          dp = nullptr;
        }
      } else {
        dp = nullptr;
      }
    }
  }
  return dp;
}

// The number of base-10 digits that can be represented by a signed 64-bit
// integer.  That is, 10^kDigits10_64 <= 2^63 - 1 < 10^(kDigits10_64 + 1).
const int kDigits10_64 = 18;

// 10^n for everything that can be represented by a signed 64-bit integer.
const std::int_fast64_t kExp10[kDigits10_64 + 1] = {
    1,
    10,
    100,
    1000,
    10000,
    100000,
    1000000,
    10000000,
    100000000,
    1000000000,
    10000000000,
    100000000000,
    1000000000000,
    10000000000000,
    100000000000000,
    1000000000000000,
    10000000000000000,
    100000000000000000,
    1000000000000000000,
};

}  // namespace

// Uses strftime(3) to format the given Time.  The following extended format
// specifiers are also supported:
//
//   - %Ez  - RFC3339-compatible numeric UTC offset (+hh:mm or -hh:mm)
//   - %E*z - Full-resolution numeric UTC offset (+hh:mm:ss or -hh:mm:ss)
//   - %E#S - Seconds with # digits of fractional precision
//   - %E*S - Seconds with full fractional precision (a literal '*')
//   - %E4Y - Four-character years (-999 ... -001, 0000, 0001 ... 9999)
//   - %ET  - The RFC3339 "date-time" separator "T"
//
// The standard specifiers from RFC3339_* (%Y, %m, %d, %H, %M, and %S) are
// handled internally for performance reasons.  strftime(3) is slow due to
// a POSIX requirement to respect changes to ${TZ}.
//
// The TZ/GNU %s extension is handled internally because strftime() has
// to use mktime() to generate it, and that assumes the local time zone.
//
// We also handle the %z and %Z specifiers to accommodate platforms that do
// not support the tm_gmtoff and tm_zone extensions to std::tm.
//
// Requires that zero() <= fs < seconds(1).
std::string format(const std::string& format, const time_point<seconds>& tp,
                   const detail::femtoseconds& fs, const time_zone& tz) {
  std::string result;
  result.reserve(format.size());  // A reasonable guess for the result size.
  const time_zone::absolute_lookup al = tz.lookup(tp);
  const std::tm tm = ToTM(al);

  // Scratch buffer for internal conversions.
  char buf[3 + kDigits10_64];  // enough for longest conversion
  char* const ep = buf + sizeof(buf);
  char* bp;  // works back from ep

  // Maintain three, disjoint subsequences that span format.
  //   [format.begin() ... pending) : already formatted into result
  //   [pending ... cur) : formatting pending, but no special cases
  //   [cur ... format.end()) : unexamined
  // Initially, everything is in the unexamined part.
  const char* pending = format.c_str();  // NUL terminated
  const char* cur = pending;
  const char* end = pending + format.length();

  while (cur != end) {  // while something is unexamined
    // Moves cur to the next percent sign.
    const char* start = cur;
    while (cur != end && *cur != '%') ++cur;

    // If the new pending text is all ordinary, copy it out.
    if (cur != start && pending == start) {
      result.append(pending, static_cast<std::size_t>(cur - pending));
      pending = start = cur;
    }

    // Span the sequential percent signs.
    const char* percent = cur;
    while (cur != end && *cur == '%') ++cur;

    // If the new pending text is all percents, copy out one
    // percent for every matched pair, then skip those pairs.
    if (cur != start && pending == start) {
      std::size_t escaped = static_cast<std::size_t>(cur - pending) / 2;
      result.append(pending, escaped);
      pending += escaped * 2;
      // Also copy out a single trailing percent.
      if (pending != cur && cur == end) {
        result.push_back(*pending++);
      }
    }

    // Loop unless we have an unescaped percent.
    if (cur == end || (cur - percent) % 2 == 0) continue;

    // Simple specifiers that we handle ourselves.
    if (strchr("YmdeUuWwHMSzZs%", *cur)) {
      if (cur - 1 != pending) {
        FormatTM(&result, std::string(pending, cur - 1), tm);
      }
      switch (*cur) {
        case 'Y':
          // This avoids the tm.tm_year overflow problem for %Y, however
          // tm.tm_year will still be used by other specifiers like %D.
          bp = Format64(ep, 0, al.cs.year());
          result.append(bp, static_cast<std::size_t>(ep - bp));
          break;
        case 'm':
          bp = Format02d(ep, al.cs.month());
          result.append(bp, static_cast<std::size_t>(ep - bp));
          break;
        case 'd':
        case 'e':
          bp = Format02d(ep, al.cs.day());
          if (*cur == 'e' && *bp == '0') *bp = ' ';  // for Windows
          result.append(bp, static_cast<std::size_t>(ep - bp));
          break;
        case 'U':
          bp = Format02d(ep, ToWeek(civil_day(al.cs), weekday::sunday));
          result.append(bp, static_cast<std::size_t>(ep - bp));
          break;
        case 'u':
          bp = Format64(ep, 0, tm.tm_wday ? tm.tm_wday : 7);
          result.append(bp, static_cast<std::size_t>(ep - bp));
          break;
        case 'W':
          bp = Format02d(ep, ToWeek(civil_day(al.cs), weekday::monday));
          result.append(bp, static_cast<std::size_t>(ep - bp));
          break;
        case 'w':
          bp = Format64(ep, 0, tm.tm_wday);
          result.append(bp, static_cast<std::size_t>(ep - bp));
          break;
        case 'H':
          bp = Format02d(ep, al.cs.hour());
          result.append(bp, static_cast<std::size_t>(ep - bp));
          break;
        case 'M':
          bp = Format02d(ep, al.cs.minute());
          result.append(bp, static_cast<std::size_t>(ep - bp));
          break;
        case 'S':
          bp = Format02d(ep, al.cs.second());
          result.append(bp, static_cast<std::size_t>(ep - bp));
          break;
        case 'z':
          bp = FormatOffset(ep, al.offset, "");
          result.append(bp, static_cast<std::size_t>(ep - bp));
          break;
        case 'Z':
          result.append(al.abbr);
          break;
        case 's':
          bp = Format64(ep, 0, ToUnixSeconds(tp));
          result.append(bp, static_cast<std::size_t>(ep - bp));
          break;
        case '%':
          result.push_back('%');
          break;
      }
      pending = ++cur;
      continue;
    }

    // More complex specifiers that we handle ourselves.
    if (*cur == ':' && cur + 1 != end) {
      if (*(cur + 1) == 'z') {
        // Formats %:z.
        if (cur - 1 != pending) {
          FormatTM(&result, std::string(pending, cur - 1), tm);
        }
        bp = FormatOffset(ep, al.offset, ":");
        result.append(bp, static_cast<std::size_t>(ep - bp));
        pending = cur += 2;
        continue;
      }
      if (*(cur + 1) == ':' && cur + 2 != end) {
        if (*(cur + 2) == 'z') {
          // Formats %::z.
          if (cur - 1 != pending) {
            FormatTM(&result, std::string(pending, cur - 1), tm);
          }
          bp = FormatOffset(ep, al.offset, ":*");
          result.append(bp, static_cast<std::size_t>(ep - bp));
          pending = cur += 3;
          continue;
        }
        if (*(cur + 2) == ':' && cur + 3 != end) {
          if (*(cur + 3) == 'z') {
            // Formats %:::z.
            if (cur - 1 != pending) {
              FormatTM(&result, std::string(pending, cur - 1), tm);
            }
            bp = FormatOffset(ep, al.offset, ":*:");
            result.append(bp, static_cast<std::size_t>(ep - bp));
            pending = cur += 4;
            continue;
          }
        }
      }
    }

    // Loop if there is no E modifier.
    if (*cur != 'E' || ++cur == end) continue;

    // Format our extensions.
    if (*cur == 'T') {
      // Formats %ET.
      if (cur - 2 != pending) {
        FormatTM(&result, std::string(pending, cur - 2), tm);
      }
      result.append("T");
      pending = ++cur;
    } else if (*cur == 'z') {
      // Formats %Ez.
      if (cur - 2 != pending) {
        FormatTM(&result, std::string(pending, cur - 2), tm);
      }
      bp = FormatOffset(ep, al.offset, ":");
      result.append(bp, static_cast<std::size_t>(ep - bp));
      pending = ++cur;
    } else if (*cur == '*' && cur + 1 != end && *(cur + 1) == 'z') {
      // Formats %E*z.
      if (cur - 2 != pending) {
        FormatTM(&result, std::string(pending, cur - 2), tm);
      }
      bp = FormatOffset(ep, al.offset, ":*");
      result.append(bp, static_cast<std::size_t>(ep - bp));
      pending = cur += 2;
    } else if (*cur == '*' && cur + 1 != end &&
               (*(cur + 1) == 'S' || *(cur + 1) == 'f')) {
      // Formats %E*S or %E*F.
      if (cur - 2 != pending) {
        FormatTM(&result, std::string(pending, cur - 2), tm);
      }
      char* cp = ep;
      bp = Format64(cp, 15, fs.count());
      while (cp != bp && cp[-1] == '0') --cp;
      switch (*(cur + 1)) {
        case 'S':
          if (cp != bp) *--bp = '.';
          bp = Format02d(bp, al.cs.second());
          break;
        case 'f':
          if (cp == bp) *--bp = '0';
          break;
      }
      result.append(bp, static_cast<std::size_t>(cp - bp));
      pending = cur += 2;
    } else if (*cur == '4' && cur + 1 != end && *(cur + 1) == 'Y') {
      // Formats %E4Y.
      if (cur - 2 != pending) {
        FormatTM(&result, std::string(pending, cur - 2), tm);
      }
      bp = Format64(ep, 4, al.cs.year());
      result.append(bp, static_cast<std::size_t>(ep - bp));
      pending = cur += 2;
    } else if (std::isdigit(*cur)) {
      // Possibly found %E#S or %E#f.
      int n = 0;
      if (const char* np = ParseInt(cur, 0, 0, 1024, &n)) {
        if (*np == 'S' || *np == 'f') {
          // Formats %E#S or %E#f.
          if (cur - 2 != pending) {
            FormatTM(&result, std::string(pending, cur - 2), tm);
          }
          bp = ep;
          if (n > 0) {
            if (n > kDigits10_64) n = kDigits10_64;
            bp = Format64(bp, n,
                          (n > 15) ? fs.count() * kExp10[n - 15]
                                   : fs.count() / kExp10[15 - n]);
            if (*np == 'S') *--bp = '.';
          }
          if (*np == 'S') bp = Format02d(bp, al.cs.second());
          result.append(bp, static_cast<std::size_t>(ep - bp));
          pending = cur = ++np;
        }
      }
    }
  }

  // Formats any remaining data.
  if (end != pending) {
    FormatTM(&result, std::string(pending, end), tm);
  }

  return result;
}

namespace {

const char* ParseOffset(const char* dp, const char* mode, int* offset) {
  if (dp != nullptr) {
    const char first = *dp++;
    if (first == '+' || first == '-') {
      char sep = mode[0];
      int hours = 0;
      int minutes = 0;
      int seconds = 0;
      const char* ap = ParseInt(dp, 2, 0, 23, &hours);
      if (ap != nullptr && ap - dp == 2) {
        dp = ap;
        if (sep != '\0' && *ap == sep) ++ap;
        const char* bp = ParseInt(ap, 2, 0, 59, &minutes);
        if (bp != nullptr && bp - ap == 2) {
          dp = bp;
          if (sep != '\0' && *bp == sep) ++bp;
          const char* cp = ParseInt(bp, 2, 0, 59, &seconds);
          if (cp != nullptr && cp - bp == 2) dp = cp;
        }
        *offset = ((hours * 60 + minutes) * 60) + seconds;
        if (first == '-') *offset = -*offset;
      } else {
        dp = nullptr;
      }
    } else if (first == 'Z' || first == 'z') {  // Zulu
      *offset = 0;
    } else {
      dp = nullptr;
    }
  }
  return dp;
}

const char* ParseZone(const char* dp, std::string* zone) {
  zone->clear();
  if (dp != nullptr) {
    while (*dp != '\0' && !std::isspace(*dp)) zone->push_back(*dp++);
    if (zone->empty()) dp = nullptr;
  }
  return dp;
}

const char* ParseSubSeconds(const char* dp, detail::femtoseconds* subseconds) {
  if (dp != nullptr) {
    std::int_fast64_t v = 0;
    std::int_fast64_t exp = 0;
    const char* const bp = dp;
    while (const char* cp = strchr(kDigits, *dp)) {
      int d = static_cast<int>(cp - kDigits);
      if (d >= 10) break;
      if (exp < 15) {
        exp += 1;
        v *= 10;
        v += d;
      }
      ++dp;
    }
    if (dp != bp) {
      v *= kExp10[15 - exp];
      *subseconds = detail::femtoseconds(v);
    } else {
      dp = nullptr;
    }
  }
  return dp;
}

// Parses a string into a std::tm using strptime(3).
const char* ParseTM(const char* dp, const char* fmt, std::tm* tm) {
  if (dp != nullptr) {
    dp = strptime(dp, fmt, tm);
  }
  return dp;
}

// Sets year, tm_mon and tm_mday given the year, week_num, and tm_wday,
// and the day on which weeks are defined to start.
void FromWeek(int week_num, weekday week_start, year_t* year, std::tm* tm) {
  const civil_year y(*year % 400);
  civil_day cd = prev_weekday(y, week_start);  // week 0
  cd = next_weekday(cd - 1, FromTmWday(tm->tm_wday)) + (week_num * 7);
  *year += cd.year() - y.year();
  tm->tm_mon = cd.month() - 1;
  tm->tm_mday = cd.day();
}

}  // namespace

// Uses strptime(3) to parse the given input.  Supports the same extended
// format specifiers as format(), although %E#S and %E*S are treated
// identically (and similarly for %E#f and %E*f).  %Ez and %E*z also accept
// the same inputs. %ET accepts either 'T' or 't'.
//
// The standard specifiers from RFC3339_* (%Y, %m, %d, %H, %M, and %S) are
// handled internally so that we can normally avoid strptime() altogether
// (which is particularly helpful when the native implementation is broken).
//
// The TZ/GNU %s extension is handled internally because strptime() has to
// use localtime_r() to generate it, and that assumes the local time zone.
//
// We also handle the %z specifier to accommodate platforms that do not
// support the tm_gmtoff extension to std::tm.  %Z is parsed but ignored.
bool parse(const std::string& format, const std::string& input,
           const time_zone& tz, time_point<seconds>* sec,
           detail::femtoseconds* fs, std::string* err) {
  // The unparsed input.
  const char* data = input.c_str();  // NUL terminated

  // Skips leading whitespace.
  while (std::isspace(*data)) ++data;

  const year_t kyearmax = std::numeric_limits<year_t>::max();
  const year_t kyearmin = std::numeric_limits<year_t>::min();

  // Sets default values for unspecified fields.
  bool saw_year = false;
  year_t year = 1970;
  std::tm tm{};
  tm.tm_year = 1970 - 1900;
  tm.tm_mon = 1 - 1;  // Jan
  tm.tm_mday = 1;
  tm.tm_hour = 0;
  tm.tm_min = 0;
  tm.tm_sec = 0;
  tm.tm_wday = 4;  // Thu
  tm.tm_yday = 0;
  tm.tm_isdst = 0;
  auto subseconds = detail::femtoseconds::zero();
  bool saw_offset = false;
  int offset = 0;  // No offset from passed tz.
  std::string zone = "UTC";

  const char* fmt = format.c_str();  // NUL terminated
  bool twelve_hour = false;
  bool afternoon = false;
  int week_num = -1;
  weekday week_start = weekday::sunday;

  bool saw_percent_s = false;
  std::int_fast64_t percent_s = 0;

  // Steps through format, one specifier at a time.
  while (data != nullptr && *fmt != '\0') {
    if (std::isspace(*fmt)) {
      while (std::isspace(*data)) ++data;
      while (std::isspace(*++fmt)) continue;
      continue;
    }

    if (*fmt != '%') {
      if (*data == *fmt) {
        ++data;
        ++fmt;
      } else {
        data = nullptr;
      }
      continue;
    }

    const char* percent = fmt;
    if (*++fmt == '\0') {
      data = nullptr;
      continue;
    }
    switch (*fmt++) {
      case 'Y':
        // Symmetrically with FormatTime(), directly handing %Y avoids the
        // tm.tm_year overflow problem.  However, tm.tm_year will still be
        // used by other specifiers like %D.
        data = ParseInt(data, 0, kyearmin, kyearmax, &year);
        if (data != nullptr) saw_year = true;
        continue;
      case 'm':
        data = ParseInt(data, 2, 1, 12, &tm.tm_mon);
        if (data != nullptr) tm.tm_mon -= 1;
        week_num = -1;
        continue;
      case 'd':
      case 'e':
        data = ParseInt(data, 2, 1, 31, &tm.tm_mday);
        week_num = -1;
        continue;
      case 'U':
        data = ParseInt(data, 0, 0, 53, &week_num);
        week_start = weekday::sunday;
        continue;
      case 'W':
        data = ParseInt(data, 0, 0, 53, &week_num);
        week_start = weekday::monday;
        continue;
      case 'u':
        data = ParseInt(data, 0, 1, 7, &tm.tm_wday);
        if (data != nullptr) tm.tm_wday %= 7;
        continue;
      case 'w':
        data = ParseInt(data, 0, 0, 6, &tm.tm_wday);
        continue;
      case 'H':
        data = ParseInt(data, 2, 0, 23, &tm.tm_hour);
        twelve_hour = false;
        continue;
      case 'M':
        data = ParseInt(data, 2, 0, 59, &tm.tm_min);
        continue;
      case 'S':
        data = ParseInt(data, 2, 0, 60, &tm.tm_sec);
        continue;
      case 'I':
      case 'l':
      case 'r':  // probably uses %I
        twelve_hour = true;
        break;
      case 'R':  // uses %H
      case 'T':  // uses %H
      case 'c':  // probably uses %H
      case 'X':  // probably uses %H
        twelve_hour = false;
        break;
      case 'z':
        data = ParseOffset(data, "", &offset);
        if (data != nullptr) saw_offset = true;
        continue;
      case 'Z':  // ignored; zone abbreviations are ambiguous
        data = ParseZone(data, &zone);
        continue;
      case 's':
        data =
            ParseInt(data, 0, std::numeric_limits<std::int_fast64_t>::min(),
                     std::numeric_limits<std::int_fast64_t>::max(), &percent_s);
        if (data != nullptr) saw_percent_s = true;
        continue;
      case ':':
        if (fmt[0] == 'z' ||
            (fmt[0] == ':' &&
             (fmt[1] == 'z' || (fmt[1] == ':' && fmt[2] == 'z')))) {
          data = ParseOffset(data, ":", &offset);
          if (data != nullptr) saw_offset = true;
          fmt += (fmt[0] == 'z') ? 1 : (fmt[1] == 'z') ? 2 : 3;
          continue;
        }
        break;
      case '%':
        data = (*data == '%' ? data + 1 : nullptr);
        continue;
      case 'E':
        if (fmt[0] == 'T') {
          if (*data == 'T' || *data == 't') {
            ++data;
            ++fmt;
          } else {
            data = nullptr;
          }
          continue;
        }
        if (fmt[0] == 'z' || (fmt[0] == '*' && fmt[1] == 'z')) {
          data = ParseOffset(data, ":", &offset);
          if (data != nullptr) saw_offset = true;
          fmt += (fmt[0] == 'z') ? 1 : 2;
          continue;
        }
        if (fmt[0] == '*' && fmt[1] == 'S') {
          data = ParseInt(data, 2, 0, 60, &tm.tm_sec);
          if (data != nullptr && *data == '.') {
            data = ParseSubSeconds(data + 1, &subseconds);
          }
          fmt += 2;
          continue;
        }
        if (fmt[0] == '*' && fmt[1] == 'f') {
          if (data != nullptr && std::isdigit(*data)) {
            data = ParseSubSeconds(data, &subseconds);
          }
          fmt += 2;
          continue;
        }
        if (fmt[0] == '4' && fmt[1] == 'Y') {
          const char* bp = data;
          data = ParseInt(data, 4, year_t{-999}, year_t{9999}, &year);
          if (data != nullptr) {
            if (data - bp == 4) {
              saw_year = true;
            } else {
              data = nullptr;  // stopped too soon
            }
          }
          fmt += 2;
          continue;
        }
        if (std::isdigit(*fmt)) {
          int n = 0;  // value ignored
          if (const char* np = ParseInt(fmt, 0, 0, 1024, &n)) {
            if (*np == 'S') {
              data = ParseInt(data, 2, 0, 60, &tm.tm_sec);
              if (data != nullptr && *data == '.') {
                data = ParseSubSeconds(data + 1, &subseconds);
              }
              fmt = ++np;
              continue;
            }
            if (*np == 'f') {
              if (data != nullptr && std::isdigit(*data)) {
                data = ParseSubSeconds(data, &subseconds);
              }
              fmt = ++np;
              continue;
            }
          }
        }
        if (*fmt == 'c') twelve_hour = false;  // probably uses %H
        if (*fmt == 'X') twelve_hour = false;  // probably uses %H
        if (*fmt != '\0') ++fmt;
        break;
      case 'O':
        if (*fmt == 'H') twelve_hour = false;
        if (*fmt == 'I') twelve_hour = true;
        if (*fmt != '\0') ++fmt;
        break;
    }

    // Parses the current specifier.
    const char* orig_data = data;
    std::string spec(percent, static_cast<std::size_t>(fmt - percent));
    data = ParseTM(data, spec.c_str(), &tm);

    // If we successfully parsed %p we need to remember whether the result
    // was AM or PM so that we can adjust tm_hour before time_zone::lookup().
    // So reparse the input with a known AM hour, and check if it is shifted
    // to a PM hour.
    if (spec == "%p" && data != nullptr) {
      std::string test_input = "1";
      test_input.append(orig_data, static_cast<std::size_t>(data - orig_data));
      const char* test_data = test_input.c_str();
      std::tm tmp{};
      ParseTM(test_data, "%I%p", &tmp);
      afternoon = (tmp.tm_hour == 13);
    }
  }

  // Adjust a 12-hour tm_hour value if it should be in the afternoon.
  if (twelve_hour && afternoon && tm.tm_hour < 12) {
    tm.tm_hour += 12;
  }

  if (data == nullptr) {
    if (err != nullptr) *err = "Failed to parse input";
    return false;
  }

  // Skip any remaining whitespace.
  while (std::isspace(*data)) ++data;

  // parse() must consume the entire input string.
  if (*data != '\0') {
    if (err != nullptr) *err = "Illegal trailing data in input string";
    return false;
  }

  // If we saw %s then we ignore anything else and return that time.
  if (saw_percent_s) {
    *sec = FromUnixSeconds(percent_s);
    *fs = detail::femtoseconds::zero();
    return true;
  }

  // If we saw %z, %Ez, or %E*z then we want to interpret the parsed fields
  // in UTC and then shift by that offset.  Otherwise we want to interpret
  // the fields directly in the passed time_zone.
  time_zone ptz = saw_offset ? utc_time_zone() : tz;

  // Allows a leap second of 60 to normalize forward to the following ":00".
  if (tm.tm_sec == 60) {
    tm.tm_sec -= 1;
    offset -= 1;
    subseconds = detail::femtoseconds::zero();
  }

  if (!saw_year) {
    year = year_t{tm.tm_year};
    if (year > kyearmax - 1900) {
      // Platform-dependent, maybe unreachable.
      if (err != nullptr) *err = "Out-of-range year";
      return false;
    }
    year += 1900;
  }

  // Compute year, tm.tm_mon and tm.tm_mday if we parsed a week number.
  if (week_num != -1) FromWeek(week_num, week_start, &year, &tm);

  const int month = tm.tm_mon + 1;
  civil_second cs(year, month, tm.tm_mday, tm.tm_hour, tm.tm_min, tm.tm_sec);

  // parse() should not allow normalization. Due to the restricted field
  // ranges above (see ParseInt()), the only possibility is for days to roll
  // into months. That is, parsing "Sep 31" should not produce "Oct 1".
  if (cs.month() != month || cs.day() != tm.tm_mday) {
    if (err != nullptr) *err = "Out-of-range field";
    return false;
  }

  // Accounts for the offset adjustment before converting to absolute time.
  if ((offset < 0 && cs > civil_second::max() + offset) ||
      (offset > 0 && cs < civil_second::min() + offset)) {
    if (err != nullptr) *err = "Out-of-range field";
    return false;
  }
  cs -= offset;

  const auto tp = ptz.lookup(cs).pre;
  // Checks for overflow/underflow and returns an error as necessary.
  if (tp == time_point<seconds>::max()) {
    const auto al = ptz.lookup(time_point<seconds>::max());
    if (cs > al.cs) {
      if (err != nullptr) *err = "Out-of-range field";
      return false;
    }
  }
  if (tp == time_point<seconds>::min()) {
    const auto al = ptz.lookup(time_point<seconds>::min());
    if (cs < al.cs) {
      if (err != nullptr) *err = "Out-of-range field";
      return false;
    }
  }

  *sec = tp;
  *fs = subseconds;
  return true;
}

}  // namespace detail
}  // namespace cctz
}  // namespace time_internal
ABSL_NAMESPACE_END
}  // namespace absl