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
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
// This is a part of Chrono.
// See README.md and LICENSE.txt for details.

//! ISO 8601 date and time with time zone.

#[cfg(all(feature = "alloc", not(feature = "std"), not(test)))]
use alloc::string::String;
use core::borrow::Borrow;
use core::cmp::Ordering;
use core::fmt::Write;
use core::ops::{Add, AddAssign, Sub, SubAssign};
use core::time::Duration;
use core::{fmt, hash, str};
#[cfg(feature = "std")]
use std::time::{SystemTime, UNIX_EPOCH};

#[cfg(all(feature = "unstable-locales", feature = "alloc"))]
use crate::format::Locale;
use crate::format::{
    parse, parse_and_remainder, parse_rfc3339, Fixed, Item, ParseError, ParseResult, Parsed,
    StrftimeItems, TOO_LONG,
};
#[cfg(feature = "alloc")]
use crate::format::{write_rfc2822, write_rfc3339, DelayedFormat, SecondsFormat};
use crate::naive::{Days, IsoWeek, NaiveDate, NaiveDateTime, NaiveTime};
#[cfg(feature = "clock")]
use crate::offset::Local;
use crate::offset::{FixedOffset, LocalResult, Offset, TimeZone, Utc};
#[allow(deprecated)]
use crate::Date;
use crate::{expect, try_opt};
use crate::{Datelike, Months, TimeDelta, Timelike, Weekday};

#[cfg(any(feature = "rkyv", feature = "rkyv-16", feature = "rkyv-32", feature = "rkyv-64"))]
use rkyv::{Archive, Deserialize, Serialize};

/// documented at re-export site
#[cfg(feature = "serde")]
pub(super) mod serde;

#[cfg(test)]
mod tests;

/// ISO 8601 combined date and time with time zone.
///
/// There are some constructors implemented here (the `from_*` methods), but
/// the general-purpose constructors are all via the methods on the
/// [`TimeZone`](./offset/trait.TimeZone.html) implementations.
#[derive(Clone)]
#[cfg_attr(
    any(feature = "rkyv", feature = "rkyv-16", feature = "rkyv-32", feature = "rkyv-64"),
    derive(Archive, Deserialize, Serialize),
    archive(compare(PartialEq, PartialOrd))
)]
#[cfg_attr(feature = "rkyv-validation", archive(check_bytes))]
pub struct DateTime<Tz: TimeZone> {
    datetime: NaiveDateTime,
    offset: Tz::Offset,
}

/// The minimum possible `DateTime<Utc>`.
#[deprecated(since = "0.4.20", note = "Use DateTime::MIN_UTC instead")]
pub const MIN_DATETIME: DateTime<Utc> = DateTime::<Utc>::MIN_UTC;
/// The maximum possible `DateTime<Utc>`.
#[deprecated(since = "0.4.20", note = "Use DateTime::MAX_UTC instead")]
pub const MAX_DATETIME: DateTime<Utc> = DateTime::<Utc>::MAX_UTC;

impl<Tz: TimeZone> DateTime<Tz> {
    /// Makes a new `DateTime` from its components: a `NaiveDateTime` in UTC and an `Offset`.
    ///
    /// This is a low-level method, intended for use cases such as deserializing a `DateTime` or
    /// passing it through FFI.
    ///
    /// For regular use you will probably want to use a method such as
    /// [`TimeZone::from_local_datetime`] or [`NaiveDateTime::and_local_timezone`] instead.
    ///
    /// # Example
    ///
    /// ```
    /// # #[cfg(feature = "clock")] {
    /// use chrono::{DateTime, Local};
    ///
    /// let dt = Local::now();
    /// // Get components
    /// let naive_utc = dt.naive_utc();
    /// let offset = dt.offset().clone();
    /// // Serialize, pass through FFI... and recreate the `DateTime`:
    /// let dt_new = DateTime::<Local>::from_naive_utc_and_offset(naive_utc, offset);
    /// assert_eq!(dt, dt_new);
    /// # }
    /// ```
    #[inline]
    #[must_use]
    pub const fn from_naive_utc_and_offset(
        datetime: NaiveDateTime,
        offset: Tz::Offset,
    ) -> DateTime<Tz> {
        DateTime { datetime, offset }
    }

    /// Makes a new `DateTime` from its components: a `NaiveDateTime` in UTC and an `Offset`.
    #[inline]
    #[must_use]
    #[deprecated(
        since = "0.4.27",
        note = "Use TimeZone::from_utc_datetime() or DateTime::from_naive_utc_and_offset instead"
    )]
    pub fn from_utc(datetime: NaiveDateTime, offset: Tz::Offset) -> DateTime<Tz> {
        DateTime { datetime, offset }
    }

    /// Makes a new `DateTime` from a `NaiveDateTime` in *local* time and an `Offset`.
    ///
    /// # Panics
    ///
    /// Panics if the local datetime can't be converted to UTC because it would be out of range.
    ///
    /// This can happen if `datetime` is near the end of the representable range of `NaiveDateTime`,
    /// and the offset from UTC pushes it beyond that.
    #[inline]
    #[must_use]
    #[deprecated(
        since = "0.4.27",
        note = "Use TimeZone::from_local_datetime() or NaiveDateTime::and_local_timezone instead"
    )]
    pub fn from_local(datetime: NaiveDateTime, offset: Tz::Offset) -> DateTime<Tz> {
        let datetime_utc = datetime - offset.fix();

        DateTime { datetime: datetime_utc, offset }
    }

    /// Retrieves the date component with an associated timezone.
    ///
    /// Unless you are immediately planning on turning this into a `DateTime`
    /// with the same timezone you should use the [`date_naive`](DateTime::date_naive) method.
    ///
    /// [`NaiveDate`] is a more well-defined type, and has more traits implemented on it,
    /// so should be preferred to [`Date`] any time you truly want to operate on dates.
    ///
    /// # Panics
    ///
    /// [`DateTime`] internally stores the date and time in UTC with a [`NaiveDateTime`]. This
    /// method will panic if the offset from UTC would push the local date outside of the
    /// representable range of a [`Date`].
    #[inline]
    #[deprecated(since = "0.4.23", note = "Use `date_naive()` instead")]
    #[allow(deprecated)]
    #[must_use]
    pub fn date(&self) -> Date<Tz> {
        Date::from_utc(self.naive_local().date(), self.offset.clone())
    }

    /// Retrieves the date component.
    ///
    /// # Panics
    ///
    /// [`DateTime`] internally stores the date and time in UTC with a [`NaiveDateTime`]. This
    /// method will panic if the offset from UTC would push the local date outside of the
    /// representable range of a [`NaiveDate`].
    ///
    /// # Example
    ///
    /// ```
    /// use chrono::prelude::*;
    ///
    /// let date: DateTime<Utc> = Utc.with_ymd_and_hms(2020, 1, 1, 0, 0, 0).unwrap();
    /// let other: DateTime<FixedOffset> =
    ///     FixedOffset::east_opt(23).unwrap().with_ymd_and_hms(2020, 1, 1, 0, 0, 0).unwrap();
    /// assert_eq!(date.date_naive(), other.date_naive());
    /// ```
    #[inline]
    #[must_use]
    pub fn date_naive(&self) -> NaiveDate {
        self.naive_local().date()
    }

    /// Retrieves the time component.
    #[inline]
    #[must_use]
    pub fn time(&self) -> NaiveTime {
        self.datetime.time() + self.offset.fix()
    }

    /// Returns the number of non-leap seconds since January 1, 1970 0:00:00 UTC
    /// (aka "UNIX timestamp").
    ///
    /// The reverse operation of creating a [`DateTime`] from a timestamp can be performed
    /// using [`from_timestamp`](DateTime::from_timestamp) or [`TimeZone::timestamp_opt`].
    ///
    /// ```
    /// use chrono::{DateTime, TimeZone, Utc};
    ///
    /// let dt: DateTime<Utc> = Utc.with_ymd_and_hms(2015, 5, 15, 0, 0, 0).unwrap();
    /// assert_eq!(dt.timestamp(), 1431648000);
    ///
    /// assert_eq!(DateTime::from_timestamp(dt.timestamp(), dt.timestamp_subsec_nanos()).unwrap(), dt);
    /// ```
    #[inline]
    #[must_use]
    pub const fn timestamp(&self) -> i64 {
        let gregorian_day = self.datetime.date().num_days_from_ce() as i64;
        let seconds_from_midnight = self.datetime.time().num_seconds_from_midnight() as i64;
        (gregorian_day - UNIX_EPOCH_DAY) * 86_400 + seconds_from_midnight
    }

    /// Returns the number of non-leap-milliseconds since January 1, 1970 UTC.
    ///
    /// # Example
    ///
    /// ```
    /// use chrono::{NaiveDate, Utc};
    ///
    /// let dt = NaiveDate::from_ymd_opt(1970, 1, 1)
    ///     .unwrap()
    ///     .and_hms_milli_opt(0, 0, 1, 444)
    ///     .unwrap()
    ///     .and_local_timezone(Utc)
    ///     .unwrap();
    /// assert_eq!(dt.timestamp_millis(), 1_444);
    ///
    /// let dt = NaiveDate::from_ymd_opt(2001, 9, 9)
    ///     .unwrap()
    ///     .and_hms_milli_opt(1, 46, 40, 555)
    ///     .unwrap()
    ///     .and_local_timezone(Utc)
    ///     .unwrap();
    /// assert_eq!(dt.timestamp_millis(), 1_000_000_000_555);
    /// ```
    #[inline]
    #[must_use]
    pub const fn timestamp_millis(&self) -> i64 {
        let as_ms = self.timestamp() * 1000;
        as_ms + self.timestamp_subsec_millis() as i64
    }

    /// Returns the number of non-leap-microseconds since January 1, 1970 UTC.
    ///
    /// # Example
    ///
    /// ```
    /// use chrono::{NaiveDate, Utc};
    ///
    /// let dt = NaiveDate::from_ymd_opt(1970, 1, 1)
    ///     .unwrap()
    ///     .and_hms_micro_opt(0, 0, 1, 444)
    ///     .unwrap()
    ///     .and_local_timezone(Utc)
    ///     .unwrap();
    /// assert_eq!(dt.timestamp_micros(), 1_000_444);
    ///
    /// let dt = NaiveDate::from_ymd_opt(2001, 9, 9)
    ///     .unwrap()
    ///     .and_hms_micro_opt(1, 46, 40, 555)
    ///     .unwrap()
    ///     .and_local_timezone(Utc)
    ///     .unwrap();
    /// assert_eq!(dt.timestamp_micros(), 1_000_000_000_000_555);
    /// ```
    #[inline]
    #[must_use]
    pub const fn timestamp_micros(&self) -> i64 {
        let as_us = self.timestamp() * 1_000_000;
        as_us + self.timestamp_subsec_micros() as i64
    }

    /// Returns the number of non-leap-nanoseconds since January 1, 1970 UTC.
    ///
    /// # Panics
    ///
    /// An `i64` with nanosecond precision can span a range of ~584 years. This function panics on
    /// an out of range `DateTime`.
    ///
    /// The dates that can be represented as nanoseconds are between 1677-09-21T00:12:43.145224192
    /// and 2262-04-11T23:47:16.854775807.
    #[deprecated(since = "0.4.31", note = "use `timestamp_nanos_opt()` instead")]
    #[inline]
    #[must_use]
    pub const fn timestamp_nanos(&self) -> i64 {
        expect(
            self.timestamp_nanos_opt(),
            "value can not be represented in a timestamp with nanosecond precision.",
        )
    }

    /// Returns the number of non-leap-nanoseconds since January 1, 1970 UTC.
    ///
    /// # Errors
    ///
    /// An `i64` with nanosecond precision can span a range of ~584 years. This function returns
    /// `None` on an out of range `DateTime`.
    ///
    /// The dates that can be represented as nanoseconds are between 1677-09-21T00:12:43.145224192
    /// and 2262-04-11T23:47:16.854775807.
    ///
    /// # Example
    ///
    /// ```
    /// use chrono::{NaiveDate, Utc};
    ///
    /// let dt = NaiveDate::from_ymd_opt(1970, 1, 1)
    ///     .unwrap()
    ///     .and_hms_nano_opt(0, 0, 1, 444)
    ///     .unwrap()
    ///     .and_local_timezone(Utc)
    ///     .unwrap();
    /// assert_eq!(dt.timestamp_nanos_opt(), Some(1_000_000_444));
    ///
    /// let dt = NaiveDate::from_ymd_opt(2001, 9, 9)
    ///     .unwrap()
    ///     .and_hms_nano_opt(1, 46, 40, 555)
    ///     .unwrap()
    ///     .and_local_timezone(Utc)
    ///     .unwrap();
    /// assert_eq!(dt.timestamp_nanos_opt(), Some(1_000_000_000_000_000_555));
    ///
    /// let dt = NaiveDate::from_ymd_opt(1677, 9, 21)
    ///     .unwrap()
    ///     .and_hms_nano_opt(0, 12, 43, 145_224_192)
    ///     .unwrap()
    ///     .and_local_timezone(Utc)
    ///     .unwrap();
    /// assert_eq!(dt.timestamp_nanos_opt(), Some(-9_223_372_036_854_775_808));
    ///
    /// let dt = NaiveDate::from_ymd_opt(2262, 4, 11)
    ///     .unwrap()
    ///     .and_hms_nano_opt(23, 47, 16, 854_775_807)
    ///     .unwrap()
    ///     .and_local_timezone(Utc)
    ///     .unwrap();
    /// assert_eq!(dt.timestamp_nanos_opt(), Some(9_223_372_036_854_775_807));
    ///
    /// let dt = NaiveDate::from_ymd_opt(1677, 9, 21)
    ///     .unwrap()
    ///     .and_hms_nano_opt(0, 12, 43, 145_224_191)
    ///     .unwrap()
    ///     .and_local_timezone(Utc)
    ///     .unwrap();
    /// assert_eq!(dt.timestamp_nanos_opt(), None);
    ///
    /// let dt = NaiveDate::from_ymd_opt(2262, 4, 11)
    ///     .unwrap()
    ///     .and_hms_nano_opt(23, 47, 16, 854_775_808)
    ///     .unwrap()
    ///     .and_local_timezone(Utc)
    ///     .unwrap();
    /// assert_eq!(dt.timestamp_nanos_opt(), None);
    /// ```
    #[inline]
    #[must_use]
    pub const fn timestamp_nanos_opt(&self) -> Option<i64> {
        let mut timestamp = self.timestamp();
        let mut subsec_nanos = self.timestamp_subsec_nanos() as i64;
        // `(timestamp * 1_000_000_000) + subsec_nanos` may create a temporary that underflows while
        // the final value can be represented as an `i64`.
        // As workaround we converting the negative case to:
        // `((timestamp + 1) * 1_000_000_000) + (ns - 1_000_000_000)``
        //
        // Also see <https://github.com/chronotope/chrono/issues/1289>.
        if timestamp < 0 {
            subsec_nanos -= 1_000_000_000;
            timestamp += 1;
        }
        try_opt!(timestamp.checked_mul(1_000_000_000)).checked_add(subsec_nanos)
    }

    /// Returns the number of milliseconds since the last second boundary.
    ///
    /// In event of a leap second this may exceed 999.
    #[inline]
    #[must_use]
    pub const fn timestamp_subsec_millis(&self) -> u32 {
        self.timestamp_subsec_nanos() / 1_000_000
    }

    /// Returns the number of microseconds since the last second boundary.
    ///
    /// In event of a leap second this may exceed 999,999.
    #[inline]
    #[must_use]
    pub const fn timestamp_subsec_micros(&self) -> u32 {
        self.timestamp_subsec_nanos() / 1_000
    }

    /// Returns the number of nanoseconds since the last second boundary
    ///
    /// In event of a leap second this may exceed 999,999,999.
    #[inline]
    #[must_use]
    pub const fn timestamp_subsec_nanos(&self) -> u32 {
        self.datetime.time().nanosecond()
    }

    /// Retrieves an associated offset from UTC.
    #[inline]
    #[must_use]
    pub const fn offset(&self) -> &Tz::Offset {
        &self.offset
    }

    /// Retrieves an associated time zone.
    #[inline]
    #[must_use]
    pub fn timezone(&self) -> Tz {
        TimeZone::from_offset(&self.offset)
    }

    /// Changes the associated time zone.
    /// The returned `DateTime` references the same instant of time from the perspective of the
    /// provided time zone.
    #[inline]
    #[must_use]
    pub fn with_timezone<Tz2: TimeZone>(&self, tz: &Tz2) -> DateTime<Tz2> {
        tz.from_utc_datetime(&self.datetime)
    }

    /// Fix the offset from UTC to its current value, dropping the associated timezone information.
    /// This it useful for converting a generic `DateTime<Tz: Timezone>` to `DateTime<FixedOffset>`.
    #[inline]
    #[must_use]
    pub fn fixed_offset(&self) -> DateTime<FixedOffset> {
        self.with_timezone(&self.offset().fix())
    }

    /// Turn this `DateTime` into a `DateTime<Utc>`, dropping the offset and associated timezone
    /// information.
    #[inline]
    #[must_use]
    pub const fn to_utc(&self) -> DateTime<Utc> {
        DateTime { datetime: self.datetime, offset: Utc }
    }

    /// Adds given `TimeDelta` to the current date and time.
    ///
    /// # Errors
    ///
    /// Returns `None` if the resulting date would be out of range.
    #[inline]
    #[must_use]
    pub fn checked_add_signed(self, rhs: TimeDelta) -> Option<DateTime<Tz>> {
        let datetime = self.datetime.checked_add_signed(rhs)?;
        let tz = self.timezone();
        Some(tz.from_utc_datetime(&datetime))
    }

    /// Adds given `Months` to the current date and time.
    ///
    /// Uses the last day of the month if the day does not exist in the resulting month.
    ///
    /// See [`NaiveDate::checked_add_months`] for more details on behavior.
    ///
    /// # Errors
    ///
    /// Returns `None` if:
    /// - The local time at the resulting date does not exist or is ambiguous, for example during a
    ///   daylight saving time transition.
    /// - The resulting UTC datetime would be out of range.
    /// - The resulting local datetime would be out of range (unless `months` is zero).
    #[must_use]
    pub fn checked_add_months(self, months: Months) -> Option<DateTime<Tz>> {
        // `NaiveDate::checked_add_months` has a fast path for `Months(0)` that does not validate
        // the resulting date, with which we can return `Some` even for an out of range local
        // datetime.
        self.overflowing_naive_local()
            .checked_add_months(months)?
            .and_local_timezone(Tz::from_offset(&self.offset))
            .single()
    }

    /// Subtracts given `TimeDelta` from the current date and time.
    ///
    /// # Errors
    ///
    /// Returns `None` if the resulting date would be out of range.
    #[inline]
    #[must_use]
    pub fn checked_sub_signed(self, rhs: TimeDelta) -> Option<DateTime<Tz>> {
        let datetime = self.datetime.checked_sub_signed(rhs)?;
        let tz = self.timezone();
        Some(tz.from_utc_datetime(&datetime))
    }

    /// Subtracts given `Months` from the current date and time.
    ///
    /// Uses the last day of the month if the day does not exist in the resulting month.
    ///
    /// See [`NaiveDate::checked_sub_months`] for more details on behavior.
    ///
    /// # Errors
    ///
    /// Returns `None` if:
    /// - The local time at the resulting date does not exist or is ambiguous, for example during a
    ///   daylight saving time transition.
    /// - The resulting UTC datetime would be out of range.
    /// - The resulting local datetime would be out of range (unless `months` is zero).
    #[must_use]
    pub fn checked_sub_months(self, months: Months) -> Option<DateTime<Tz>> {
        // `NaiveDate::checked_sub_months` has a fast path for `Months(0)` that does not validate
        // the resulting date, with which we can return `Some` even for an out of range local
        // datetime.
        self.overflowing_naive_local()
            .checked_sub_months(months)?
            .and_local_timezone(Tz::from_offset(&self.offset))
            .single()
    }

    /// Add a duration in [`Days`] to the date part of the `DateTime`.
    ///
    /// # Errors
    ///
    /// Returns `None` if:
    /// - The local time at the resulting date does not exist or is ambiguous, for example during a
    ///   daylight saving time transition.
    /// - The resulting UTC datetime would be out of range.
    /// - The resulting local datetime would be out of range (unless `days` is zero).
    #[must_use]
    pub fn checked_add_days(self, days: Days) -> Option<Self> {
        if days == Days::new(0) {
            return Some(self);
        }
        // `NaiveDate::add_days` has a fast path if the result remains within the same year, that
        // does not validate the resulting date. This allows us to return `Some` even for an out of
        // range local datetime when adding `Days(0)`.
        self.overflowing_naive_local()
            .checked_add_days(days)
            .and_then(|dt| self.timezone().from_local_datetime(&dt).single())
            .filter(|dt| dt <= &DateTime::<Utc>::MAX_UTC)
    }

    /// Subtract a duration in [`Days`] from the date part of the `DateTime`.
    ///
    /// # Errors
    ///
    /// Returns `None` if:
    /// - The local time at the resulting date does not exist or is ambiguous, for example during a
    ///   daylight saving time transition.
    /// - The resulting UTC datetime would be out of range.
    /// - The resulting local datetime would be out of range (unless `days` is zero).
    #[must_use]
    pub fn checked_sub_days(self, days: Days) -> Option<Self> {
        // `NaiveDate::add_days` has a fast path if the result remains within the same year, that
        // does not validate the resulting date. This allows us to return `Some` even for an out of
        // range local datetime when adding `Days(0)`.
        self.overflowing_naive_local()
            .checked_sub_days(days)
            .and_then(|dt| self.timezone().from_local_datetime(&dt).single())
            .filter(|dt| dt >= &DateTime::<Utc>::MIN_UTC)
    }

    /// Subtracts another `DateTime` from the current date and time.
    /// This does not overflow or underflow at all.
    #[inline]
    #[must_use]
    pub fn signed_duration_since<Tz2: TimeZone>(
        self,
        rhs: impl Borrow<DateTime<Tz2>>,
    ) -> TimeDelta {
        self.datetime.signed_duration_since(rhs.borrow().datetime)
    }

    /// Returns a view to the naive UTC datetime.
    #[inline]
    #[must_use]
    pub const fn naive_utc(&self) -> NaiveDateTime {
        self.datetime
    }

    /// Returns a view to the naive local datetime.
    ///
    /// # Panics
    ///
    /// [`DateTime`] internally stores the date and time in UTC with a [`NaiveDateTime`]. This
    /// method will panic if the offset from UTC would push the local datetime outside of the
    /// representable range of a [`NaiveDateTime`].
    #[inline]
    #[must_use]
    pub fn naive_local(&self) -> NaiveDateTime {
        self.datetime
            .checked_add_offset(self.offset.fix())
            .expect("Local time out of range for `NaiveDateTime`")
    }

    /// Returns the naive local datetime.
    ///
    /// This makes use of the buffer space outside of the representable range of values of
    /// `NaiveDateTime`. The result can be used as intermediate value, but should never be exposed
    /// outside chrono.
    #[inline]
    #[must_use]
    pub(crate) fn overflowing_naive_local(&self) -> NaiveDateTime {
        self.datetime.overflowing_add_offset(self.offset.fix())
    }

    /// Retrieve the elapsed years from now to the given [`DateTime`].
    ///
    /// # Errors
    ///
    /// Returns `None` if `base < self`.
    #[must_use]
    pub fn years_since(&self, base: Self) -> Option<u32> {
        let mut years = self.year() - base.year();
        let earlier_time =
            (self.month(), self.day(), self.time()) < (base.month(), base.day(), base.time());

        years -= match earlier_time {
            true => 1,
            false => 0,
        };

        match years >= 0 {
            true => Some(years as u32),
            false => None,
        }
    }

    /// Returns an RFC 2822 date and time string such as `Tue, 1 Jul 2003 10:52:37 +0200`.
    ///
    /// # Panics
    ///
    /// Panics if the date can not be represented in this format: the year may not be negative and
    /// can not have more than 4 digits.
    #[cfg(feature = "alloc")]
    #[must_use]
    pub fn to_rfc2822(&self) -> String {
        let mut result = String::with_capacity(32);
        write_rfc2822(&mut result, self.overflowing_naive_local(), self.offset.fix())
            .expect("writing rfc2822 datetime to string should never fail");
        result
    }

    /// Returns an RFC 3339 and ISO 8601 date and time string such as `1996-12-19T16:39:57-08:00`.
    #[cfg(feature = "alloc")]
    #[must_use]
    pub fn to_rfc3339(&self) -> String {
        // For some reason a string with a capacity less than 32 is ca 20% slower when benchmarking.
        let mut result = String::with_capacity(32);
        let naive = self.overflowing_naive_local();
        let offset = self.offset.fix();
        write_rfc3339(&mut result, naive, offset, SecondsFormat::AutoSi, false)
            .expect("writing rfc3339 datetime to string should never fail");
        result
    }

    /// Return an RFC 3339 and ISO 8601 date and time string with subseconds
    /// formatted as per `SecondsFormat`.
    ///
    /// If `use_z` is true and the timezone is UTC (offset 0), uses `Z` as
    /// per [`Fixed::TimezoneOffsetColonZ`]. If `use_z` is false, uses
    /// [`Fixed::TimezoneOffsetColon`]
    ///
    /// # Examples
    ///
    /// ```rust
    /// # use chrono::{FixedOffset, SecondsFormat, TimeZone, NaiveDate};
    /// let dt = NaiveDate::from_ymd_opt(2018, 1, 26)
    ///     .unwrap()
    ///     .and_hms_micro_opt(18, 30, 9, 453_829)
    ///     .unwrap()
    ///     .and_utc();
    /// assert_eq!(dt.to_rfc3339_opts(SecondsFormat::Millis, false), "2018-01-26T18:30:09.453+00:00");
    /// assert_eq!(dt.to_rfc3339_opts(SecondsFormat::Millis, true), "2018-01-26T18:30:09.453Z");
    /// assert_eq!(dt.to_rfc3339_opts(SecondsFormat::Secs, true), "2018-01-26T18:30:09Z");
    ///
    /// let pst = FixedOffset::east_opt(8 * 60 * 60).unwrap();
    /// let dt = pst
    ///     .from_local_datetime(
    ///         &NaiveDate::from_ymd_opt(2018, 1, 26)
    ///             .unwrap()
    ///             .and_hms_micro_opt(10, 30, 9, 453_829)
    ///             .unwrap(),
    ///     )
    ///     .unwrap();
    /// assert_eq!(dt.to_rfc3339_opts(SecondsFormat::Secs, true), "2018-01-26T10:30:09+08:00");
    /// ```
    #[cfg(feature = "alloc")]
    #[must_use]
    pub fn to_rfc3339_opts(&self, secform: SecondsFormat, use_z: bool) -> String {
        let mut result = String::with_capacity(38);
        write_rfc3339(&mut result, self.naive_local(), self.offset.fix(), secform, use_z)
            .expect("writing rfc3339 datetime to string should never fail");
        result
    }

    /// Set the time to a new fixed time on the existing date.
    ///
    /// # Errors
    ///
    /// Returns `LocalResult::None` if the datetime is at the edge of the representable range for a
    /// `DateTime`, and `with_time` would push the value in UTC out of range.
    ///
    /// # Example
    ///
    /// ```
    /// # #[cfg(feature = "clock")] {
    /// use chrono::{Local, NaiveTime};
    ///
    /// let noon = NaiveTime::from_hms_opt(12, 0, 0).unwrap();
    /// let today_noon = Local::now().with_time(noon);
    /// let today_midnight = Local::now().with_time(NaiveTime::MIN);
    ///
    /// assert_eq!(today_noon.single().unwrap().time(), noon);
    /// assert_eq!(today_midnight.single().unwrap().time(), NaiveTime::MIN);
    /// # }
    /// ```
    #[must_use]
    pub fn with_time(&self, time: NaiveTime) -> LocalResult<Self> {
        self.timezone().from_local_datetime(&self.overflowing_naive_local().date().and_time(time))
    }

    /// The minimum possible `DateTime<Utc>`.
    pub const MIN_UTC: DateTime<Utc> = DateTime { datetime: NaiveDateTime::MIN, offset: Utc };
    /// The maximum possible `DateTime<Utc>`.
    pub const MAX_UTC: DateTime<Utc> = DateTime { datetime: NaiveDateTime::MAX, offset: Utc };
}

impl DateTime<Utc> {
    /// Makes a new `DateTime<Utc>` from the number of non-leap seconds
    /// since January 1, 1970 0:00:00 UTC (aka "UNIX timestamp")
    /// and the number of nanoseconds since the last whole non-leap second.
    ///
    /// This is guaranteed to round-trip with regard to [`timestamp`](DateTime::timestamp) and
    /// [`timestamp_subsec_nanos`](DateTime::timestamp_subsec_nanos).
    ///
    /// If you need to create a `DateTime` with a [`TimeZone`] different from [`Utc`], use
    /// [`TimeZone::timestamp_opt`] or [`DateTime::with_timezone`].
    ///
    /// The nanosecond part can exceed 1,000,000,000 in order to represent a
    /// [leap second](NaiveTime#leap-second-handling), but only when `secs % 60 == 59`.
    /// (The true "UNIX timestamp" cannot represent a leap second unambiguously.)
    ///
    /// # Errors
    ///
    /// Returns `None` on out-of-range number of seconds and/or
    /// invalid nanosecond, otherwise returns `Some(DateTime {...})`.
    ///
    /// # Example
    ///
    /// ```
    /// use chrono::DateTime;
    ///
    /// let dt = DateTime::from_timestamp(1431648000, 0).expect("invalid timestamp");
    ///
    /// assert_eq!(dt.to_string(), "2015-05-15 00:00:00 UTC");
    /// assert_eq!(DateTime::from_timestamp(dt.timestamp(), dt.timestamp_subsec_nanos()).unwrap(), dt);
    /// ```
    #[inline]
    #[must_use]
    pub const fn from_timestamp(secs: i64, nsecs: u32) -> Option<Self> {
        let days = secs.div_euclid(86_400) + UNIX_EPOCH_DAY;
        let secs = secs.rem_euclid(86_400);
        if days < i32::MIN as i64 || days > i32::MAX as i64 {
            return None;
        }
        let date = try_opt!(NaiveDate::from_num_days_from_ce_opt(days as i32));
        let time = try_opt!(NaiveTime::from_num_seconds_from_midnight_opt(secs as u32, nsecs));
        Some(date.and_time(time).and_utc())
    }

    /// Makes a new `DateTime<Utc>` from the number of non-leap milliseconds
    /// since January 1, 1970 0:00:00.000 UTC (aka "UNIX timestamp").
    ///
    /// This is guaranteed to round-trip with [`timestamp_millis`](DateTime::timestamp_millis).
    ///
    /// If you need to create a `DateTime` with a [`TimeZone`] different from [`Utc`], use
    /// [`TimeZone::timestamp_millis_opt`] or [`DateTime::with_timezone`].
    ///
    /// # Errors
    ///
    /// Returns `None` on out-of-range number of milliseconds, otherwise returns `Some(DateTime {...})`.
    ///
    /// # Example
    ///
    /// ```
    /// use chrono::DateTime;
    ///
    /// let dt = DateTime::from_timestamp_millis(947638923004).expect("invalid timestamp");
    ///
    /// assert_eq!(dt.to_string(), "2000-01-12 01:02:03.004 UTC");
    /// assert_eq!(DateTime::from_timestamp_millis(dt.timestamp_millis()).unwrap(), dt);
    /// ```
    #[inline]
    #[must_use]
    pub const fn from_timestamp_millis(millis: i64) -> Option<Self> {
        let secs = millis.div_euclid(1000);
        let nsecs = millis.rem_euclid(1000) as u32 * 1_000_000;
        Self::from_timestamp(secs, nsecs)
    }

    /// Creates a new `DateTime<Utc>` from the number of non-leap microseconds
    /// since January 1, 1970 0:00:00.000 UTC (aka "UNIX timestamp").
    ///
    /// This is guaranteed to round-trip with [`timestamp_micros`](DateTime::timestamp_micros).
    ///
    /// If you need to create a `DateTime` with a [`TimeZone`] different from [`Utc`], use
    /// [`TimeZone::timestamp_micros`] or [`DateTime::with_timezone`].
    ///
    /// # Errors
    ///
    /// Returns `None` if the number of microseconds would be out of range for a `NaiveDateTime`
    /// (more than ca. 262,000 years away from common era)
    ///
    /// # Example
    ///
    /// ```
    /// use chrono::DateTime;
    ///
    /// let timestamp_micros: i64 = 1662921288000000; // Sun, 11 Sep 2022 18:34:48 UTC
    /// let dt = DateTime::from_timestamp_micros(timestamp_micros);
    /// assert!(dt.is_some());
    /// assert_eq!(timestamp_micros, dt.expect("invalid timestamp").timestamp_micros());
    ///
    /// // Negative timestamps (before the UNIX epoch) are supported as well.
    /// let timestamp_micros: i64 = -2208936075000000; // Mon, 1 Jan 1900 14:38:45 UTC
    /// let dt = DateTime::from_timestamp_micros(timestamp_micros);
    /// assert!(dt.is_some());
    /// assert_eq!(timestamp_micros, dt.expect("invalid timestamp").timestamp_micros());
    /// ```
    #[inline]
    #[must_use]
    pub const fn from_timestamp_micros(micros: i64) -> Option<Self> {
        let secs = micros.div_euclid(1_000_000);
        let nsecs = micros.rem_euclid(1_000_000) as u32 * 1000;
        Self::from_timestamp(secs, nsecs)
    }

    /// Creates a new [`DateTime<Utc>`] from the number of non-leap microseconds
    /// since January 1, 1970 0:00:00.000 UTC (aka "UNIX timestamp").
    ///
    /// This is guaranteed to round-trip with [`timestamp_nanos`](DateTime::timestamp_nanos).
    ///
    /// If you need to create a `DateTime` with a [`TimeZone`] different from [`Utc`], use
    /// [`TimeZone::timestamp_nanos`] or [`DateTime::with_timezone`].
    ///
    /// The UNIX epoch starts on midnight, January 1, 1970, UTC.
    ///
    /// An `i64` with nanosecond precision can span a range of ~584 years. Because all values can
    /// be represented as a `DateTime` this method never fails.
    ///
    /// # Example
    ///
    /// ```
    /// use chrono::DateTime;
    ///
    /// let timestamp_nanos: i64 = 1662921288_000_000_000; // Sun, 11 Sep 2022 18:34:48 UTC
    /// let dt = DateTime::from_timestamp_nanos(timestamp_nanos);
    /// assert_eq!(timestamp_nanos, dt.timestamp_nanos_opt().unwrap());
    ///
    /// // Negative timestamps (before the UNIX epoch) are supported as well.
    /// let timestamp_nanos: i64 = -2208936075_000_000_000; // Mon, 1 Jan 1900 14:38:45 UTC
    /// let dt = DateTime::from_timestamp_nanos(timestamp_nanos);
    /// assert_eq!(timestamp_nanos, dt.timestamp_nanos_opt().unwrap());
    /// ```
    #[inline]
    #[must_use]
    pub const fn from_timestamp_nanos(nanos: i64) -> Self {
        let secs = nanos.div_euclid(1_000_000_000);
        let nsecs = nanos.rem_euclid(1_000_000_000) as u32;
        expect(Self::from_timestamp(secs, nsecs), "timestamp in nanos is always in range")
    }

    /// The Unix Epoch, 1970-01-01 00:00:00 UTC.
    pub const UNIX_EPOCH: Self = Self { datetime: NaiveDateTime::UNIX_EPOCH, offset: Utc };
}

impl Default for DateTime<Utc> {
    fn default() -> Self {
        Utc.from_utc_datetime(&NaiveDateTime::default())
    }
}

#[cfg(feature = "clock")]
impl Default for DateTime<Local> {
    fn default() -> Self {
        Local.from_utc_datetime(&NaiveDateTime::default())
    }
}

impl Default for DateTime<FixedOffset> {
    fn default() -> Self {
        FixedOffset::west_opt(0).unwrap().from_utc_datetime(&NaiveDateTime::default())
    }
}

/// Convert a `DateTime<Utc>` instance into a `DateTime<FixedOffset>` instance.
impl From<DateTime<Utc>> for DateTime<FixedOffset> {
    /// Convert this `DateTime<Utc>` instance into a `DateTime<FixedOffset>` instance.
    ///
    /// Conversion is done via [`DateTime::with_timezone`]. Note that the converted value returned by
    /// this will be created with a fixed timezone offset of 0.
    fn from(src: DateTime<Utc>) -> Self {
        src.with_timezone(&FixedOffset::east_opt(0).unwrap())
    }
}

/// Convert a `DateTime<Utc>` instance into a `DateTime<Local>` instance.
#[cfg(feature = "clock")]
impl From<DateTime<Utc>> for DateTime<Local> {
    /// Convert this `DateTime<Utc>` instance into a `DateTime<Local>` instance.
    ///
    /// Conversion is performed via [`DateTime::with_timezone`], accounting for the difference in timezones.
    fn from(src: DateTime<Utc>) -> Self {
        src.with_timezone(&Local)
    }
}

/// Convert a `DateTime<FixedOffset>` instance into a `DateTime<Utc>` instance.
impl From<DateTime<FixedOffset>> for DateTime<Utc> {
    /// Convert this `DateTime<FixedOffset>` instance into a `DateTime<Utc>` instance.
    ///
    /// Conversion is performed via [`DateTime::with_timezone`], accounting for the timezone
    /// difference.
    fn from(src: DateTime<FixedOffset>) -> Self {
        src.with_timezone(&Utc)
    }
}

/// Convert a `DateTime<FixedOffset>` instance into a `DateTime<Local>` instance.
#[cfg(feature = "clock")]
impl From<DateTime<FixedOffset>> for DateTime<Local> {
    /// Convert this `DateTime<FixedOffset>` instance into a `DateTime<Local>` instance.
    ///
    /// Conversion is performed via [`DateTime::with_timezone`]. Returns the equivalent value in local
    /// time.
    fn from(src: DateTime<FixedOffset>) -> Self {
        src.with_timezone(&Local)
    }
}

/// Convert a `DateTime<Local>` instance into a `DateTime<Utc>` instance.
#[cfg(feature = "clock")]
impl From<DateTime<Local>> for DateTime<Utc> {
    /// Convert this `DateTime<Local>` instance into a `DateTime<Utc>` instance.
    ///
    /// Conversion is performed via [`DateTime::with_timezone`], accounting for the difference in
    /// timezones.
    fn from(src: DateTime<Local>) -> Self {
        src.with_timezone(&Utc)
    }
}

/// Convert a `DateTime<Local>` instance into a `DateTime<FixedOffset>` instance.
#[cfg(feature = "clock")]
impl From<DateTime<Local>> for DateTime<FixedOffset> {
    /// Convert this `DateTime<Local>` instance into a `DateTime<FixedOffset>` instance.
    ///
    /// Conversion is performed via [`DateTime::with_timezone`].
    fn from(src: DateTime<Local>) -> Self {
        src.with_timezone(&src.offset().fix())
    }
}

/// Maps the local datetime to other datetime with given conversion function.
fn map_local<Tz: TimeZone, F>(dt: &DateTime<Tz>, mut f: F) -> Option<DateTime<Tz>>
where
    F: FnMut(NaiveDateTime) -> Option<NaiveDateTime>,
{
    f(dt.overflowing_naive_local())
        .and_then(|datetime| dt.timezone().from_local_datetime(&datetime).single())
        .filter(|dt| dt >= &DateTime::<Utc>::MIN_UTC && dt <= &DateTime::<Utc>::MAX_UTC)
}

impl DateTime<FixedOffset> {
    /// Parses an RFC 2822 date-and-time string into a `DateTime<FixedOffset>` value.
    ///
    /// This parses valid RFC 2822 datetime strings (such as `Tue, 1 Jul 2003 10:52:37 +0200`)
    /// and returns a new [`DateTime`] instance with the parsed timezone as the [`FixedOffset`].
    ///
    /// RFC 2822 is the internet message standard that specifies the representation of times in HTTP
    /// and email headers. It is the 2001 revision of RFC 822, and is itself revised as RFC 5322 in
    /// 2008.
    ///
    /// # Support for the obsolete date format
    ///
    /// - A 2-digit year is interpreted to be a year in 1950-2049.
    /// - The standard allows comments and whitespace between many of the tokens. See [4.3] and
    ///   [Appendix A.5]
    /// - Single letter 'military' time zone names are parsed as a `-0000` offset.
    ///   They were defined with the wrong sign in RFC 822 and corrected in RFC 2822. But because
    ///   the meaning is now ambiguous, the standard says they should be be considered as `-0000`
    ///   unless there is out-of-band information confirming their meaning.
    ///   The exception is `Z`, which remains identical to `+0000`.
    ///
    /// [4.3]: https://www.rfc-editor.org/rfc/rfc2822#section-4.3
    /// [Appendix A.5]: https://www.rfc-editor.org/rfc/rfc2822#appendix-A.5
    ///
    /// # Example
    ///
    /// ```
    /// # use chrono::{DateTime, FixedOffset, TimeZone};
    /// assert_eq!(
    ///     DateTime::parse_from_rfc2822("Wed, 18 Feb 2015 23:16:09 GMT").unwrap(),
    ///     FixedOffset::east_opt(0).unwrap().with_ymd_and_hms(2015, 2, 18, 23, 16, 9).unwrap()
    /// );
    /// ```
    pub fn parse_from_rfc2822(s: &str) -> ParseResult<DateTime<FixedOffset>> {
        const ITEMS: &[Item<'static>] = &[Item::Fixed(Fixed::RFC2822)];
        let mut parsed = Parsed::new();
        parse(&mut parsed, s, ITEMS.iter())?;
        parsed.to_datetime()
    }

    /// Parses an RFC 3339 date-and-time string into a `DateTime<FixedOffset>` value.
    ///
    /// Parses all valid RFC 3339 values (as well as the subset of valid ISO 8601 values that are
    /// also valid RFC 3339 date-and-time values) and returns a new [`DateTime`] with a
    /// [`FixedOffset`] corresponding to the parsed timezone. While RFC 3339 values come in a wide
    /// variety of shapes and sizes, `1996-12-19T16:39:57-08:00` is an example of the most commonly
    /// encountered variety of RFC 3339 formats.
    ///
    /// Why isn't this named `parse_from_iso8601`? That's because ISO 8601 allows representing
    /// values in a wide range of formats, only some of which represent actual date-and-time
    /// instances (rather than periods, ranges, dates, or times). Some valid ISO 8601 values are
    /// also simultaneously valid RFC 3339 values, but not all RFC 3339 values are valid ISO 8601
    /// values (or the other way around).
    pub fn parse_from_rfc3339(s: &str) -> ParseResult<DateTime<FixedOffset>> {
        let mut parsed = Parsed::new();
        let (s, _) = parse_rfc3339(&mut parsed, s)?;
        if !s.is_empty() {
            return Err(TOO_LONG);
        }
        parsed.to_datetime()
    }

    /// Parses a string from a user-specified format into a `DateTime<FixedOffset>` value.
    ///
    /// Note that this method *requires a timezone* in the input string. See
    /// [`NaiveDateTime::parse_from_str`](./naive/struct.NaiveDateTime.html#method.parse_from_str)
    /// for a version that does not require a timezone in the to-be-parsed str. The returned
    /// [`DateTime`] value will have a [`FixedOffset`] reflecting the parsed timezone.
    ///
    /// See the [`format::strftime` module](./format/strftime/index.html) for supported format
    /// sequences.
    ///
    /// # Example
    ///
    /// ```rust
    /// use chrono::{DateTime, FixedOffset, NaiveDate, TimeZone};
    ///
    /// let dt = DateTime::parse_from_str("1983 Apr 13 12:09:14.274 +0000", "%Y %b %d %H:%M:%S%.3f %z");
    /// assert_eq!(
    ///     dt,
    ///     Ok(FixedOffset::east_opt(0)
    ///         .unwrap()
    ///         .from_local_datetime(
    ///             &NaiveDate::from_ymd_opt(1983, 4, 13)
    ///                 .unwrap()
    ///                 .and_hms_milli_opt(12, 9, 14, 274)
    ///                 .unwrap()
    ///         )
    ///         .unwrap())
    /// );
    /// ```
    pub fn parse_from_str(s: &str, fmt: &str) -> ParseResult<DateTime<FixedOffset>> {
        let mut parsed = Parsed::new();
        parse(&mut parsed, s, StrftimeItems::new(fmt))?;
        parsed.to_datetime()
    }

    /// Parses a string from a user-specified format into a `DateTime<FixedOffset>` value, and a
    /// slice with the remaining portion of the string.
    ///
    /// Note that this method *requires a timezone* in the input string. See
    /// [`NaiveDateTime::parse_and_remainder`] for a version that does not
    /// require a timezone in `s`. The returned [`DateTime`] value will have a [`FixedOffset`]
    /// reflecting the parsed timezone.
    ///
    /// See the [`format::strftime` module](./format/strftime/index.html) for supported format
    /// sequences.
    ///
    /// Similar to [`parse_from_str`](#method.parse_from_str).
    ///
    /// # Example
    ///
    /// ```rust
    /// # use chrono::{DateTime, FixedOffset, TimeZone};
    /// let (datetime, remainder) = DateTime::parse_and_remainder(
    ///     "2015-02-18 23:16:09 +0200 trailing text",
    ///     "%Y-%m-%d %H:%M:%S %z",
    /// )
    /// .unwrap();
    /// assert_eq!(
    ///     datetime,
    ///     FixedOffset::east_opt(2 * 3600).unwrap().with_ymd_and_hms(2015, 2, 18, 23, 16, 9).unwrap()
    /// );
    /// assert_eq!(remainder, " trailing text");
    /// ```
    pub fn parse_and_remainder<'a>(
        s: &'a str,
        fmt: &str,
    ) -> ParseResult<(DateTime<FixedOffset>, &'a str)> {
        let mut parsed = Parsed::new();
        let remainder = parse_and_remainder(&mut parsed, s, StrftimeItems::new(fmt))?;
        parsed.to_datetime().map(|d| (d, remainder))
    }
}

impl<Tz: TimeZone> DateTime<Tz>
where
    Tz::Offset: fmt::Display,
{
    /// Formats the combined date and time with the specified formatting items.
    #[cfg(feature = "alloc")]
    #[inline]
    #[must_use]
    pub fn format_with_items<'a, I, B>(&self, items: I) -> DelayedFormat<I>
    where
        I: Iterator<Item = B> + Clone,
        B: Borrow<Item<'a>>,
    {
        let local = self.overflowing_naive_local();
        DelayedFormat::new_with_offset(Some(local.date()), Some(local.time()), &self.offset, items)
    }

    /// Formats the combined date and time per the specified format string.
    ///
    /// See the [`crate::format::strftime`] module for the supported escape sequences.
    ///
    /// # Example
    /// ```rust
    /// use chrono::prelude::*;
    ///
    /// let date_time: DateTime<Utc> = Utc.with_ymd_and_hms(2017, 04, 02, 12, 50, 32).unwrap();
    /// let formatted = format!("{}", date_time.format("%d/%m/%Y %H:%M"));
    /// assert_eq!(formatted, "02/04/2017 12:50");
    /// ```
    #[cfg(feature = "alloc")]
    #[inline]
    #[must_use]
    pub fn format<'a>(&self, fmt: &'a str) -> DelayedFormat<StrftimeItems<'a>> {
        self.format_with_items(StrftimeItems::new(fmt))
    }

    /// Formats the combined date and time with the specified formatting items and locale.
    #[cfg(all(feature = "unstable-locales", feature = "alloc"))]
    #[inline]
    #[must_use]
    pub fn format_localized_with_items<'a, I, B>(
        &self,
        items: I,
        locale: Locale,
    ) -> DelayedFormat<I>
    where
        I: Iterator<Item = B> + Clone,
        B: Borrow<Item<'a>>,
    {
        let local = self.overflowing_naive_local();
        DelayedFormat::new_with_offset_and_locale(
            Some(local.date()),
            Some(local.time()),
            &self.offset,
            items,
            locale,
        )
    }

    /// Formats the combined date and time per the specified format string and
    /// locale.
    ///
    /// See the [`crate::format::strftime`] module on the supported escape
    /// sequences.
    #[cfg(all(feature = "unstable-locales", feature = "alloc"))]
    #[inline]
    #[must_use]
    pub fn format_localized<'a>(
        &self,
        fmt: &'a str,
        locale: Locale,
    ) -> DelayedFormat<StrftimeItems<'a>> {
        self.format_localized_with_items(StrftimeItems::new_with_locale(fmt, locale), locale)
    }
}

impl<Tz: TimeZone> Datelike for DateTime<Tz> {
    #[inline]
    fn year(&self) -> i32 {
        self.overflowing_naive_local().year()
    }
    #[inline]
    fn month(&self) -> u32 {
        self.overflowing_naive_local().month()
    }
    #[inline]
    fn month0(&self) -> u32 {
        self.overflowing_naive_local().month0()
    }
    #[inline]
    fn day(&self) -> u32 {
        self.overflowing_naive_local().day()
    }
    #[inline]
    fn day0(&self) -> u32 {
        self.overflowing_naive_local().day0()
    }
    #[inline]
    fn ordinal(&self) -> u32 {
        self.overflowing_naive_local().ordinal()
    }
    #[inline]
    fn ordinal0(&self) -> u32 {
        self.overflowing_naive_local().ordinal0()
    }
    #[inline]
    fn weekday(&self) -> Weekday {
        self.overflowing_naive_local().weekday()
    }
    #[inline]
    fn iso_week(&self) -> IsoWeek {
        self.overflowing_naive_local().iso_week()
    }

    #[inline]
    /// Makes a new `DateTime` with the year number changed, while keeping the same month and day.
    ///
    /// See also the [`NaiveDate::with_year`] method.
    ///
    /// # Errors
    ///
    /// Returns `None` if:
    /// - The resulting date does not exist (February 29 in a non-leap year).
    /// - The local time at the resulting date does not exist or is ambiguous, for example during a
    ///   daylight saving time transition.
    /// - The resulting UTC datetime would be out of range.
    /// - The resulting local datetime would be out of range (unless the year remains the same).
    fn with_year(&self, year: i32) -> Option<DateTime<Tz>> {
        map_local(self, |dt| match dt.year() == year {
            true => Some(dt),
            false => dt.with_year(year),
        })
    }

    /// Makes a new `DateTime` with the month number (starting from 1) changed.
    ///
    /// Don't combine multiple `Datelike::with_*` methods. The intermediate value may not exist.
    ///
    /// See also the [`NaiveDate::with_month`] method.
    ///
    /// # Errors
    ///
    /// Returns `None` if:
    /// - The resulting date does not exist (for example `month(4)` when day of the month is 31).
    /// - The value for `month` is invalid.
    /// - The local time at the resulting date does not exist or is ambiguous, for example during a
    ///   daylight saving time transition.
    #[inline]
    fn with_month(&self, month: u32) -> Option<DateTime<Tz>> {
        map_local(self, |datetime| datetime.with_month(month))
    }

    /// Makes a new `DateTime` with the month number (starting from 0) changed.
    ///
    /// See also the [`NaiveDate::with_month0`] method.
    ///
    /// # Errors
    ///
    /// Returns `None` if:
    /// - The resulting date does not exist (for example `month0(3)` when day of the month is 31).
    /// - The value for `month0` is invalid.
    /// - The local time at the resulting date does not exist or is ambiguous, for example during a
    ///   daylight saving time transition.
    #[inline]
    fn with_month0(&self, month0: u32) -> Option<DateTime<Tz>> {
        map_local(self, |datetime| datetime.with_month0(month0))
    }

    /// Makes a new `DateTime` with the day of month (starting from 1) changed.
    ///
    /// See also the [`NaiveDate::with_day`] method.
    ///
    /// # Errors
    ///
    /// Returns `None` if:
    /// - The resulting date does not exist (for example `day(31)` in April).
    /// - The value for `day` is invalid.
    /// - The local time at the resulting date does not exist or is ambiguous, for example during a
    ///   daylight saving time transition.
    #[inline]
    fn with_day(&self, day: u32) -> Option<DateTime<Tz>> {
        map_local(self, |datetime| datetime.with_day(day))
    }

    /// Makes a new `DateTime` with the day of month (starting from 0) changed.
    ///
    /// See also the [`NaiveDate::with_day0`] method.
    ///
    /// # Errors
    ///
    /// Returns `None` if:
    /// - The resulting date does not exist (for example `day(30)` in April).
    /// - The value for `day0` is invalid.
    /// - The local time at the resulting date does not exist or is ambiguous, for example during a
    ///   daylight saving time transition.
    #[inline]
    fn with_day0(&self, day0: u32) -> Option<DateTime<Tz>> {
        map_local(self, |datetime| datetime.with_day0(day0))
    }

    /// Makes a new `DateTime` with the day of year (starting from 1) changed.
    ///
    /// See also the [`NaiveDate::with_ordinal`] method.
    ///
    /// # Errors
    ///
    /// Returns `None` if:
    /// - The resulting date does not exist (`with_ordinal(366)` in a non-leap year).
    /// - The value for `ordinal` is invalid.
    /// - The local time at the resulting date does not exist or is ambiguous, for example during a
    ///   daylight saving time transition.
    #[inline]
    fn with_ordinal(&self, ordinal: u32) -> Option<DateTime<Tz>> {
        map_local(self, |datetime| datetime.with_ordinal(ordinal))
    }

    /// Makes a new `DateTime` with the day of year (starting from 0) changed.
    ///
    /// See also the [`NaiveDate::with_ordinal0`] method.
    ///
    /// # Errors
    ///
    /// Returns `None` if:
    /// - The resulting date does not exist (`with_ordinal0(365)` in a non-leap year).
    /// - The value for `ordinal0` is invalid.
    /// - The local time at the resulting date does not exist or is ambiguous, for example during a
    ///   daylight saving time transition.
    #[inline]
    fn with_ordinal0(&self, ordinal0: u32) -> Option<DateTime<Tz>> {
        map_local(self, |datetime| datetime.with_ordinal0(ordinal0))
    }
}

impl<Tz: TimeZone> Timelike for DateTime<Tz> {
    #[inline]
    fn hour(&self) -> u32 {
        self.overflowing_naive_local().hour()
    }
    #[inline]
    fn minute(&self) -> u32 {
        self.overflowing_naive_local().minute()
    }
    #[inline]
    fn second(&self) -> u32 {
        self.overflowing_naive_local().second()
    }
    #[inline]
    fn nanosecond(&self) -> u32 {
        self.overflowing_naive_local().nanosecond()
    }

    /// Makes a new `DateTime` with the hour number changed.
    ///
    /// See also the [`NaiveTime::with_hour`] method.
    ///
    /// # Errors
    ///
    /// Returns `None` if:
    /// - The value for `hour` is invalid.
    /// - The local time at the resulting date does not exist or is ambiguous, for example during a
    ///   daylight saving time transition.
    #[inline]
    fn with_hour(&self, hour: u32) -> Option<DateTime<Tz>> {
        map_local(self, |datetime| datetime.with_hour(hour))
    }

    /// Makes a new `DateTime` with the minute number changed.
    ///
    /// See also the [`NaiveTime::with_minute`] method.
    ///
    /// # Errors
    ///
    /// - The value for `minute` is invalid.
    /// - The local time at the resulting date does not exist or is ambiguous, for example during a
    ///   daylight saving time transition.
    #[inline]
    fn with_minute(&self, min: u32) -> Option<DateTime<Tz>> {
        map_local(self, |datetime| datetime.with_minute(min))
    }

    /// Makes a new `DateTime` with the second number changed.
    ///
    /// As with the [`second`](#method.second) method,
    /// the input range is restricted to 0 through 59.
    ///
    /// See also the [`NaiveTime::with_second`] method.
    ///
    /// # Errors
    ///
    /// Returns `None` if:
    /// - The value for `second` is invalid.
    /// - The local time at the resulting date does not exist or is ambiguous, for example during a
    ///   daylight saving time transition.
    #[inline]
    fn with_second(&self, sec: u32) -> Option<DateTime<Tz>> {
        map_local(self, |datetime| datetime.with_second(sec))
    }

    /// Makes a new `DateTime` with nanoseconds since the whole non-leap second changed.
    ///
    /// Returns `None` when the resulting `NaiveDateTime` would be invalid.
    /// As with the [`NaiveDateTime::nanosecond`] method,
    /// the input range can exceed 1,000,000,000 for leap seconds.
    ///
    /// See also the [`NaiveTime::with_nanosecond`] method.
    ///
    /// # Errors
    ///
    /// Returns `None` if `nanosecond >= 2,000,000,000`.
    #[inline]
    fn with_nanosecond(&self, nano: u32) -> Option<DateTime<Tz>> {
        map_local(self, |datetime| datetime.with_nanosecond(nano))
    }
}

// We don't store a field with the `Tz` type, so it doesn't need to influence whether `DateTime` can
// be `Copy`. Implement it manually if the two types we do have are `Copy`.
impl<Tz: TimeZone> Copy for DateTime<Tz>
where
    <Tz as TimeZone>::Offset: Copy,
    NaiveDateTime: Copy,
{
}

impl<Tz: TimeZone, Tz2: TimeZone> PartialEq<DateTime<Tz2>> for DateTime<Tz> {
    fn eq(&self, other: &DateTime<Tz2>) -> bool {
        self.datetime == other.datetime
    }
}

impl<Tz: TimeZone> Eq for DateTime<Tz> {}

impl<Tz: TimeZone, Tz2: TimeZone> PartialOrd<DateTime<Tz2>> for DateTime<Tz> {
    /// Compare two DateTimes based on their true time, ignoring time zones
    ///
    /// # Example
    ///
    /// ```
    /// use chrono::prelude::*;
    ///
    /// let earlier = Utc
    ///     .with_ymd_and_hms(2015, 5, 15, 2, 0, 0)
    ///     .unwrap()
    ///     .with_timezone(&FixedOffset::west_opt(1 * 3600).unwrap());
    /// let later = Utc
    ///     .with_ymd_and_hms(2015, 5, 15, 3, 0, 0)
    ///     .unwrap()
    ///     .with_timezone(&FixedOffset::west_opt(5 * 3600).unwrap());
    ///
    /// assert_eq!(earlier.to_string(), "2015-05-15 01:00:00 -01:00");
    /// assert_eq!(later.to_string(), "2015-05-14 22:00:00 -05:00");
    ///
    /// assert!(later > earlier);
    /// ```
    fn partial_cmp(&self, other: &DateTime<Tz2>) -> Option<Ordering> {
        self.datetime.partial_cmp(&other.datetime)
    }
}

impl<Tz: TimeZone> Ord for DateTime<Tz> {
    fn cmp(&self, other: &DateTime<Tz>) -> Ordering {
        self.datetime.cmp(&other.datetime)
    }
}

impl<Tz: TimeZone> hash::Hash for DateTime<Tz> {
    fn hash<H: hash::Hasher>(&self, state: &mut H) {
        self.datetime.hash(state)
    }
}

/// Add `TimeDelta` to `DateTime`.
///
/// As a part of Chrono's [leap second handling], the addition assumes that **there is no leap
/// second ever**, except when the `NaiveDateTime` itself represents a leap  second in which case
/// the assumption becomes that **there is exactly a single leap second ever**.
///
/// # Panics
///
/// Panics if the resulting date would be out of range.
/// Consider using [`DateTime<Tz>::checked_add_signed`] to get an `Option` instead.
impl<Tz: TimeZone> Add<TimeDelta> for DateTime<Tz> {
    type Output = DateTime<Tz>;

    #[inline]
    fn add(self, rhs: TimeDelta) -> DateTime<Tz> {
        self.checked_add_signed(rhs).expect("`DateTime + TimeDelta` overflowed")
    }
}

/// Add `std::time::Duration` to `DateTime`.
///
/// As a part of Chrono's [leap second handling], the addition assumes that **there is no leap
/// second ever**, except when the `NaiveDateTime` itself represents a leap  second in which case
/// the assumption becomes that **there is exactly a single leap second ever**.
///
/// # Panics
///
/// Panics if the resulting date would be out of range.
/// Consider using [`DateTime<Tz>::checked_add_signed`] to get an `Option` instead.
impl<Tz: TimeZone> Add<Duration> for DateTime<Tz> {
    type Output = DateTime<Tz>;

    #[inline]
    fn add(self, rhs: Duration) -> DateTime<Tz> {
        let rhs = TimeDelta::from_std(rhs)
            .expect("overflow converting from core::time::Duration to TimeDelta");
        self.checked_add_signed(rhs).expect("`DateTime + TimeDelta` overflowed")
    }
}

/// Add-assign `chrono::Duration` to `DateTime`.
///
/// As a part of Chrono's [leap second handling], the addition assumes that **there is no leap
/// second ever**, except when the `NaiveDateTime` itself represents a leap  second in which case
/// the assumption becomes that **there is exactly a single leap second ever**.
///
/// # Panics
///
/// Panics if the resulting date would be out of range.
/// Consider using [`DateTime<Tz>::checked_add_signed`] to get an `Option` instead.
impl<Tz: TimeZone> AddAssign<TimeDelta> for DateTime<Tz> {
    #[inline]
    fn add_assign(&mut self, rhs: TimeDelta) {
        let datetime =
            self.datetime.checked_add_signed(rhs).expect("`DateTime + TimeDelta` overflowed");
        let tz = self.timezone();
        *self = tz.from_utc_datetime(&datetime);
    }
}

/// Add-assign `std::time::Duration` to `DateTime`.
///
/// As a part of Chrono's [leap second handling], the addition assumes that **there is no leap
/// second ever**, except when the `NaiveDateTime` itself represents a leap  second in which case
/// the assumption becomes that **there is exactly a single leap second ever**.
///
/// # Panics
///
/// Panics if the resulting date would be out of range.
/// Consider using [`DateTime<Tz>::checked_add_signed`] to get an `Option` instead.
impl<Tz: TimeZone> AddAssign<Duration> for DateTime<Tz> {
    #[inline]
    fn add_assign(&mut self, rhs: Duration) {
        let rhs = TimeDelta::from_std(rhs)
            .expect("overflow converting from core::time::Duration to TimeDelta");
        *self += rhs;
    }
}

/// Add `FixedOffset` to the datetime value of `DateTime` (offset remains unchanged).
///
/// # Panics
///
/// Panics if the resulting date would be out of range.
impl<Tz: TimeZone> Add<FixedOffset> for DateTime<Tz> {
    type Output = DateTime<Tz>;

    #[inline]
    fn add(mut self, rhs: FixedOffset) -> DateTime<Tz> {
        self.datetime =
            self.naive_utc().checked_add_offset(rhs).expect("`DateTime + FixedOffset` overflowed");
        self
    }
}

/// Add `Months` to `DateTime`.
///
/// The result will be clamped to valid days in the resulting month, see `checked_add_months` for
/// details.
///
/// # Panics
///
/// Panics if:
/// - The resulting date would be out of range.
/// - The local time at the resulting date does not exist or is ambiguous, for example during a
///   daylight saving time transition.
///
/// Strongly consider using [`DateTime<Tz>::checked_add_months`] to get an `Option` instead.
impl<Tz: TimeZone> Add<Months> for DateTime<Tz> {
    type Output = DateTime<Tz>;

    fn add(self, rhs: Months) -> Self::Output {
        self.checked_add_months(rhs).expect("`DateTime + Months` out of range")
    }
}

/// Subtract `TimeDelta` from `DateTime`.
///
/// This is the same as the addition with a negated `TimeDelta`.
///
/// As a part of Chrono's [leap second handling] the subtraction assumes that **there is no leap
/// second ever**, except when the `DateTime` itself represents a leap second in which case
/// the assumption becomes that **there is exactly a single leap second ever**.
///
/// # Panics
///
/// Panics if the resulting date would be out of range.
/// Consider using [`DateTime<Tz>::checked_sub_signed`] to get an `Option` instead.
impl<Tz: TimeZone> Sub<TimeDelta> for DateTime<Tz> {
    type Output = DateTime<Tz>;

    #[inline]
    fn sub(self, rhs: TimeDelta) -> DateTime<Tz> {
        self.checked_sub_signed(rhs).expect("`DateTime - TimeDelta` overflowed")
    }
}

/// Subtract `std::time::Duration` from `DateTime`.
///
/// As a part of Chrono's [leap second handling] the subtraction assumes that **there is no leap
/// second ever**, except when the `DateTime` itself represents a leap second in which case
/// the assumption becomes that **there is exactly a single leap second ever**.
///
/// # Panics
///
/// Panics if the resulting date would be out of range.
/// Consider using [`DateTime<Tz>::checked_sub_signed`] to get an `Option` instead.
impl<Tz: TimeZone> Sub<Duration> for DateTime<Tz> {
    type Output = DateTime<Tz>;

    #[inline]
    fn sub(self, rhs: Duration) -> DateTime<Tz> {
        let rhs = TimeDelta::from_std(rhs)
            .expect("overflow converting from core::time::Duration to TimeDelta");
        self.checked_sub_signed(rhs).expect("`DateTime - TimeDelta` overflowed")
    }
}

/// Subtract-assign `TimeDelta` from `DateTime`.
///
/// This is the same as the addition with a negated `TimeDelta`.
///
/// As a part of Chrono's [leap second handling], the addition assumes that **there is no leap
/// second ever**, except when the `DateTime` itself represents a leap  second in which case
/// the assumption becomes that **there is exactly a single leap second ever**.
///
/// # Panics
///
/// Panics if the resulting date would be out of range.
/// Consider using [`DateTime<Tz>::checked_sub_signed`] to get an `Option` instead.
impl<Tz: TimeZone> SubAssign<TimeDelta> for DateTime<Tz> {
    #[inline]
    fn sub_assign(&mut self, rhs: TimeDelta) {
        let datetime =
            self.datetime.checked_sub_signed(rhs).expect("`DateTime - TimeDelta` overflowed");
        let tz = self.timezone();
        *self = tz.from_utc_datetime(&datetime)
    }
}

/// Subtract-assign `std::time::Duration` from `DateTime`.
///
/// As a part of Chrono's [leap second handling], the addition assumes that **there is no leap
/// second ever**, except when the `DateTime` itself represents a leap  second in which case
/// the assumption becomes that **there is exactly a single leap second ever**.
///
/// # Panics
///
/// Panics if the resulting date would be out of range.
/// Consider using [`DateTime<Tz>::checked_sub_signed`] to get an `Option` instead.
impl<Tz: TimeZone> SubAssign<Duration> for DateTime<Tz> {
    #[inline]
    fn sub_assign(&mut self, rhs: Duration) {
        let rhs = TimeDelta::from_std(rhs)
            .expect("overflow converting from core::time::Duration to TimeDelta");
        *self -= rhs;
    }
}

/// Subtract `FixedOffset` from the datetime value of `DateTime` (offset remains unchanged).
///
/// # Panics
///
/// Panics if the resulting date would be out of range.
impl<Tz: TimeZone> Sub<FixedOffset> for DateTime<Tz> {
    type Output = DateTime<Tz>;

    #[inline]
    fn sub(mut self, rhs: FixedOffset) -> DateTime<Tz> {
        self.datetime =
            self.naive_utc().checked_sub_offset(rhs).expect("`DateTime - FixedOffset` overflowed");
        self
    }
}

/// Subtract `Months` from `DateTime`.
///
/// The result will be clamped to valid days in the resulting month, see
/// [`DateTime<Tz>::checked_sub_months`] for details.
///
/// # Panics
///
/// Panics if:
/// - The resulting date would be out of range.
/// - The local time at the resulting date does not exist or is ambiguous, for example during a
///   daylight saving time transition.
///
/// Strongly consider using [`DateTime<Tz>::checked_sub_months`] to get an `Option` instead.
impl<Tz: TimeZone> Sub<Months> for DateTime<Tz> {
    type Output = DateTime<Tz>;

    fn sub(self, rhs: Months) -> Self::Output {
        self.checked_sub_months(rhs).expect("`DateTime - Months` out of range")
    }
}

impl<Tz: TimeZone> Sub<DateTime<Tz>> for DateTime<Tz> {
    type Output = TimeDelta;

    #[inline]
    fn sub(self, rhs: DateTime<Tz>) -> TimeDelta {
        self.signed_duration_since(rhs)
    }
}

impl<Tz: TimeZone> Sub<&DateTime<Tz>> for DateTime<Tz> {
    type Output = TimeDelta;

    #[inline]
    fn sub(self, rhs: &DateTime<Tz>) -> TimeDelta {
        self.signed_duration_since(rhs)
    }
}

/// Add `Days` to `NaiveDateTime`.
///
/// # Panics
///
/// Panics if:
/// - The resulting date would be out of range.
/// - The local time at the resulting date does not exist or is ambiguous, for example during a
///   daylight saving time transition.
///
/// Strongly consider using `DateTime<Tz>::checked_sub_days` to get an `Option` instead.
impl<Tz: TimeZone> Add<Days> for DateTime<Tz> {
    type Output = DateTime<Tz>;

    fn add(self, days: Days) -> Self::Output {
        self.checked_add_days(days).expect("`DateTime + Days` out of range")
    }
}

/// Subtract `Days` from `DateTime`.
///
/// # Panics
///
/// Panics if:
/// - The resulting date would be out of range.
/// - The local time at the resulting date does not exist or is ambiguous, for example during a
///   daylight saving time transition.
///
/// Strongly consider using `DateTime<Tz>::checked_sub_days` to get an `Option` instead.
impl<Tz: TimeZone> Sub<Days> for DateTime<Tz> {
    type Output = DateTime<Tz>;

    fn sub(self, days: Days) -> Self::Output {
        self.checked_sub_days(days).expect("`DateTime - Days` out of range")
    }
}

impl<Tz: TimeZone> fmt::Debug for DateTime<Tz> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        self.overflowing_naive_local().fmt(f)?;
        self.offset.fmt(f)
    }
}

// `fmt::Debug` is hand implemented for the `rkyv::Archive` variant of `DateTime` because
// deriving a trait recursively does not propagate trait defined associated types with their own
// constraints:
// In our case `<<Tz as offset::TimeZone>::Offset as Archive>::Archived`
// cannot be formatted using `{:?}` because it doesn't implement `Debug`.
// See below for further discussion:
// * https://github.com/rust-lang/rust/issues/26925
// * https://github.com/rkyv/rkyv/issues/333
// * https://github.com/dtolnay/syn/issues/370
#[cfg(feature = "rkyv-validation")]
impl<Tz: TimeZone> fmt::Debug for ArchivedDateTime<Tz>
where
    Tz: Archive,
    <Tz as Archive>::Archived: fmt::Debug,
    <<Tz as TimeZone>::Offset as Archive>::Archived: fmt::Debug,
    <Tz as TimeZone>::Offset: fmt::Debug + Archive,
{
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_struct("ArchivedDateTime")
            .field("datetime", &self.datetime)
            .field("offset", &self.offset)
            .finish()
    }
}

impl<Tz: TimeZone> fmt::Display for DateTime<Tz>
where
    Tz::Offset: fmt::Display,
{
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        self.overflowing_naive_local().fmt(f)?;
        f.write_char(' ')?;
        self.offset.fmt(f)
    }
}

/// Accepts a relaxed form of RFC3339.
/// A space or a 'T' are accepted as the separator between the date and time
/// parts.
///
/// All of these examples are equivalent:
/// ```
/// # use chrono::{DateTime, Utc};
/// "2012-12-12T12:12:12Z".parse::<DateTime<Utc>>()?;
/// "2012-12-12 12:12:12Z".parse::<DateTime<Utc>>()?;
/// "2012-12-12 12:12:12+0000".parse::<DateTime<Utc>>()?;
/// "2012-12-12 12:12:12+00:00".parse::<DateTime<Utc>>()?;
/// # Ok::<(), chrono::ParseError>(())
/// ```
impl str::FromStr for DateTime<Utc> {
    type Err = ParseError;

    fn from_str(s: &str) -> ParseResult<DateTime<Utc>> {
        s.parse::<DateTime<FixedOffset>>().map(|dt| dt.with_timezone(&Utc))
    }
}

/// Accepts a relaxed form of RFC3339.
/// A space or a 'T' are accepted as the separator between the date and time
/// parts.
///
/// All of these examples are equivalent:
/// ```
/// # use chrono::{DateTime, Local};
/// "2012-12-12T12:12:12Z".parse::<DateTime<Local>>()?;
/// "2012-12-12 12:12:12Z".parse::<DateTime<Local>>()?;
/// "2012-12-12 12:12:12+0000".parse::<DateTime<Local>>()?;
/// "2012-12-12 12:12:12+00:00".parse::<DateTime<Local>>()?;
/// # Ok::<(), chrono::ParseError>(())
/// ```
#[cfg(feature = "clock")]
impl str::FromStr for DateTime<Local> {
    type Err = ParseError;

    fn from_str(s: &str) -> ParseResult<DateTime<Local>> {
        s.parse::<DateTime<FixedOffset>>().map(|dt| dt.with_timezone(&Local))
    }
}

#[cfg(feature = "std")]
impl From<SystemTime> for DateTime<Utc> {
    fn from(t: SystemTime) -> DateTime<Utc> {
        let (sec, nsec) = match t.duration_since(UNIX_EPOCH) {
            Ok(dur) => (dur.as_secs() as i64, dur.subsec_nanos()),
            Err(e) => {
                // unlikely but should be handled
                let dur = e.duration();
                let (sec, nsec) = (dur.as_secs() as i64, dur.subsec_nanos());
                if nsec == 0 {
                    (-sec, 0)
                } else {
                    (-sec - 1, 1_000_000_000 - nsec)
                }
            }
        };
        Utc.timestamp_opt(sec, nsec).unwrap()
    }
}

#[cfg(feature = "clock")]
impl From<SystemTime> for DateTime<Local> {
    fn from(t: SystemTime) -> DateTime<Local> {
        DateTime::<Utc>::from(t).with_timezone(&Local)
    }
}

#[cfg(feature = "std")]
impl<Tz: TimeZone> From<DateTime<Tz>> for SystemTime {
    fn from(dt: DateTime<Tz>) -> SystemTime {
        let sec = dt.timestamp();
        let nsec = dt.timestamp_subsec_nanos();
        if sec < 0 {
            // unlikely but should be handled
            UNIX_EPOCH - Duration::new(-sec as u64, 0) + Duration::new(0, nsec)
        } else {
            UNIX_EPOCH + Duration::new(sec as u64, nsec)
        }
    }
}

#[cfg(all(
    target_arch = "wasm32",
    feature = "wasmbind",
    not(any(target_os = "emscripten", target_os = "wasi"))
))]
impl From<js_sys::Date> for DateTime<Utc> {
    fn from(date: js_sys::Date) -> DateTime<Utc> {
        DateTime::<Utc>::from(&date)
    }
}

#[cfg(all(
    target_arch = "wasm32",
    feature = "wasmbind",
    not(any(target_os = "emscripten", target_os = "wasi"))
))]
impl From<&js_sys::Date> for DateTime<Utc> {
    fn from(date: &js_sys::Date) -> DateTime<Utc> {
        Utc.timestamp_millis_opt(date.get_time() as i64).unwrap()
    }
}

#[cfg(all(
    target_arch = "wasm32",
    feature = "wasmbind",
    not(any(target_os = "emscripten", target_os = "wasi"))
))]
impl From<DateTime<Utc>> for js_sys::Date {
    /// Converts a `DateTime<Utc>` to a JS `Date`. The resulting value may be lossy,
    /// any values that have a millisecond timestamp value greater/less than ±8,640,000,000,000,000
    /// (April 20, 271821 BCE ~ September 13, 275760 CE) will become invalid dates in JS.
    fn from(date: DateTime<Utc>) -> js_sys::Date {
        let js_millis = wasm_bindgen::JsValue::from_f64(date.timestamp_millis() as f64);
        js_sys::Date::new(&js_millis)
    }
}

// Note that implementation of Arbitrary cannot be simply derived for DateTime<Tz>, due to
// the nontrivial bound <Tz as TimeZone>::Offset: Arbitrary.
#[cfg(all(feature = "arbitrary", feature = "std"))]
impl<'a, Tz> arbitrary::Arbitrary<'a> for DateTime<Tz>
where
    Tz: TimeZone,
    <Tz as TimeZone>::Offset: arbitrary::Arbitrary<'a>,
{
    fn arbitrary(u: &mut arbitrary::Unstructured<'a>) -> arbitrary::Result<DateTime<Tz>> {
        let datetime = NaiveDateTime::arbitrary(u)?;
        let offset = <Tz as TimeZone>::Offset::arbitrary(u)?;
        Ok(DateTime::from_naive_utc_and_offset(datetime, offset))
    }
}

/// Number of days between Januari 1, 1970 and December 31, 1 BCE which we define to be day 0.
/// 4 full leap year cycles until December 31, 1600     4 * 146097 = 584388
/// 1 day until January 1, 1601                                           1
/// 369 years until Januari 1, 1970                      369 * 365 = 134685
/// of which floor(369 / 4) are leap years          floor(369 / 4) =     92
/// except for 1700, 1800 and 1900                                       -3 +
///                                                                  --------
///                                                                  719163
const UNIX_EPOCH_DAY: i64 = 719_163;