1// Copyright 2018 The Abseil Authors.
2//
3// Licensed under the Apache License, Version 2.0 (the "License");
4// you may not use this file except in compliance with the License.
5// You may obtain a copy of the License at
6//
7// https://www.apache.org/licenses/LICENSE-2.0
8//
9// Unless required by applicable law or agreed to in writing, software
10// distributed under the License is distributed on an "AS IS" BASIS,
11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12// See the License for the specific language governing permissions and
13// limitations under the License.
14//
15// -----------------------------------------------------------------------------
16// File: civil_time.h
17// -----------------------------------------------------------------------------
18//
19// This header file defines abstractions for computing with "civil time".
20// The term "civil time" refers to the legally recognized human-scale time
21// that is represented by the six fields `YYYY-MM-DD hh:mm:ss`. A "date"
22// is perhaps the most common example of a civil time (represented here as
23// an `absl::CivilDay`).
24//
25// Modern-day civil time follows the Gregorian Calendar and is a
26// time-zone-independent concept: a civil time of "2015-06-01 12:00:00", for
27// example, is not tied to a time zone. Put another way, a civil time does not
28// map to a unique point in time; a civil time must be mapped to an absolute
29// time *through* a time zone.
30//
31// Because a civil time is what most people think of as "time," it is common to
32// map absolute times to civil times to present to users.
33//
34// Time zones define the relationship between absolute and civil times. Given an
35// absolute or civil time and a time zone, you can compute the other time:
36//
37// Civil Time = F(Absolute Time, Time Zone)
38// Absolute Time = G(Civil Time, Time Zone)
39//
40// The Abseil time library allows you to construct such civil times from
41// absolute times; consult time.h for such functionality.
42//
43// This library provides six classes for constructing civil-time objects, and
44// provides several helper functions for rounding, iterating, and performing
45// arithmetic on civil-time objects, while avoiding complications like
46// daylight-saving time (DST):
47//
48// * `absl::CivilSecond`
49// * `absl::CivilMinute`
50// * `absl::CivilHour`
51// * `absl::CivilDay`
52// * `absl::CivilMonth`
53// * `absl::CivilYear`
54//
55// Example:
56//
57// // Construct a civil-time object for a specific day
58// const absl::CivilDay cd(1969, 07, 20);
59//
60// // Construct a civil-time object for a specific second
61// const absl::CivilSecond cd(2018, 8, 1, 12, 0, 1);
62//
63// Note: In C++14 and later, this library is usable in a constexpr context.
64//
65// Example:
66//
67// // Valid in C++14
68// constexpr absl::CivilDay cd(1969, 07, 20);
69
70#ifndef ABSL_TIME_CIVIL_TIME_H_
71#define ABSL_TIME_CIVIL_TIME_H_
72
73#include <string>
74
75#include "absl/strings/string_view.h"
76#include "absl/time/internal/cctz/include/cctz/civil_time.h"
77
78namespace absl {
79ABSL_NAMESPACE_BEGIN
80
81namespace time_internal {
82struct second_tag : cctz::detail::second_tag {};
83struct minute_tag : second_tag, cctz::detail::minute_tag {};
84struct hour_tag : minute_tag, cctz::detail::hour_tag {};
85struct day_tag : hour_tag, cctz::detail::day_tag {};
86struct month_tag : day_tag, cctz::detail::month_tag {};
87struct year_tag : month_tag, cctz::detail::year_tag {};
88} // namespace time_internal
89
90// -----------------------------------------------------------------------------
91// CivilSecond, CivilMinute, CivilHour, CivilDay, CivilMonth, CivilYear
92// -----------------------------------------------------------------------------
93//
94// Each of these civil-time types is a simple value type with the same
95// interface for construction and the same six accessors for each of the civil
96// time fields (year, month, day, hour, minute, and second, aka YMDHMS). These
97// classes differ only in their alignment, which is indicated by the type name
98// and specifies the field on which arithmetic operates.
99//
100// CONSTRUCTION
101//
102// Each of the civil-time types can be constructed in two ways: by directly
103// passing to the constructor up to six integers representing the YMDHMS fields,
104// or by copying the YMDHMS fields from a differently aligned civil-time type.
105// Omitted fields are assigned their minimum valid value. Hours, minutes, and
106// seconds will be set to 0, month and day will be set to 1. Since there is no
107// minimum year, the default is 1970.
108//
109// Examples:
110//
111// absl::CivilDay default_value; // 1970-01-01 00:00:00
112//
113// absl::CivilDay a(2015, 2, 3); // 2015-02-03 00:00:00
114// absl::CivilDay b(2015, 2, 3, 4, 5, 6); // 2015-02-03 00:00:00
115// absl::CivilDay c(2015); // 2015-01-01 00:00:00
116//
117// absl::CivilSecond ss(2015, 2, 3, 4, 5, 6); // 2015-02-03 04:05:06
118// absl::CivilMinute mm(ss); // 2015-02-03 04:05:00
119// absl::CivilHour hh(mm); // 2015-02-03 04:00:00
120// absl::CivilDay d(hh); // 2015-02-03 00:00:00
121// absl::CivilMonth m(d); // 2015-02-01 00:00:00
122// absl::CivilYear y(m); // 2015-01-01 00:00:00
123//
124// m = absl::CivilMonth(y); // 2015-01-01 00:00:00
125// d = absl::CivilDay(m); // 2015-01-01 00:00:00
126// hh = absl::CivilHour(d); // 2015-01-01 00:00:00
127// mm = absl::CivilMinute(hh); // 2015-01-01 00:00:00
128// ss = absl::CivilSecond(mm); // 2015-01-01 00:00:00
129//
130// Each civil-time class is aligned to the civil-time field indicated in the
131// class's name after normalization. Alignment is performed by setting all the
132// inferior fields to their minimum valid value (as described above). The
133// following are examples of how each of the six types would align the fields
134// representing November 22, 2015 at 12:34:56 in the afternoon. (Note: the
135// string format used here is not important; it's just a shorthand way of
136// showing the six YMDHMS fields.)
137//
138// absl::CivilSecond : 2015-11-22 12:34:56
139// absl::CivilMinute : 2015-11-22 12:34:00
140// absl::CivilHour : 2015-11-22 12:00:00
141// absl::CivilDay : 2015-11-22 00:00:00
142// absl::CivilMonth : 2015-11-01 00:00:00
143// absl::CivilYear : 2015-01-01 00:00:00
144//
145// Each civil-time type performs arithmetic on the field to which it is
146// aligned. This means that adding 1 to an absl::CivilDay increments the day
147// field (normalizing as necessary), and subtracting 7 from an absl::CivilMonth
148// operates on the month field (normalizing as necessary). All arithmetic
149// produces a valid civil time. Difference requires two similarly aligned
150// civil-time objects and returns the scalar answer in units of the objects'
151// alignment. For example, the difference between two absl::CivilHour objects
152// will give an answer in units of civil hours.
153//
154// ALIGNMENT CONVERSION
155//
156// The alignment of a civil-time object cannot change, but the object may be
157// used to construct a new object with a different alignment. This is referred
158// to as "realigning". When realigning to a type with the same or more
159// precision (e.g., absl::CivilDay -> absl::CivilSecond), the conversion may be
160// performed implicitly since no information is lost. However, if information
161// could be discarded (e.g., CivilSecond -> CivilDay), the conversion must
162// be explicit at the call site.
163//
164// Examples:
165//
166// void UseDay(absl::CivilDay day);
167//
168// absl::CivilSecond cs;
169// UseDay(cs); // Won't compile because data may be discarded
170// UseDay(absl::CivilDay(cs)); // OK: explicit conversion
171//
172// absl::CivilDay cd;
173// UseDay(cd); // OK: no conversion needed
174//
175// absl::CivilMonth cm;
176// UseDay(cm); // OK: implicit conversion to absl::CivilDay
177//
178// NORMALIZATION
179//
180// Normalization takes invalid values and adjusts them to produce valid values.
181// Within the civil-time library, integer arguments passed to the Civil*
182// constructors may be out-of-range, in which case they are normalized by
183// carrying overflow into a field of courser granularity to produce valid
184// civil-time objects. This normalization enables natural arithmetic on
185// constructor arguments without worrying about the field's range.
186//
187// Examples:
188//
189// // Out-of-range; normalized to 2016-11-01
190// absl::CivilDay d(2016, 10, 32);
191// // Out-of-range, negative: normalized to 2016-10-30T23
192// absl::CivilHour h1(2016, 10, 31, -1);
193// // Normalization is cumulative: normalized to 2016-10-30T23
194// absl::CivilHour h2(2016, 10, 32, -25);
195//
196// Note: If normalization is undesired, you can signal an error by comparing
197// the constructor arguments to the normalized values returned by the YMDHMS
198// properties.
199//
200// COMPARISON
201//
202// Comparison between civil-time objects considers all six YMDHMS fields,
203// regardless of the type's alignment. Comparison between differently aligned
204// civil-time types is allowed.
205//
206// Examples:
207//
208// absl::CivilDay feb_3(2015, 2, 3); // 2015-02-03 00:00:00
209// absl::CivilDay mar_4(2015, 3, 4); // 2015-03-04 00:00:00
210// // feb_3 < mar_4
211// // absl::CivilYear(feb_3) == absl::CivilYear(mar_4)
212//
213// absl::CivilSecond feb_3_noon(2015, 2, 3, 12, 0, 0); // 2015-02-03 12:00:00
214// // feb_3 < feb_3_noon
215// // feb_3 == absl::CivilDay(feb_3_noon)
216//
217// // Iterates all the days of February 2015.
218// for (absl::CivilDay d(2015, 2, 1); d < absl::CivilMonth(2015, 3); ++d) {
219// // ...
220// }
221//
222// ARITHMETIC
223//
224// Civil-time types support natural arithmetic operators such as addition,
225// subtraction, and difference. Arithmetic operates on the civil-time field
226// indicated in the type's name. Difference operators require arguments with
227// the same alignment and return the answer in units of the alignment.
228//
229// Example:
230//
231// absl::CivilDay a(2015, 2, 3);
232// ++a; // 2015-02-04 00:00:00
233// --a; // 2015-02-03 00:00:00
234// absl::CivilDay b = a + 1; // 2015-02-04 00:00:00
235// absl::CivilDay c = 1 + b; // 2015-02-05 00:00:00
236// int n = c - a; // n = 2 (civil days)
237// int m = c - absl::CivilMonth(c); // Won't compile: different types.
238//
239// ACCESSORS
240//
241// Each civil-time type has accessors for all six of the civil-time fields:
242// year, month, day, hour, minute, and second.
243//
244// civil_year_t year()
245// int month()
246// int day()
247// int hour()
248// int minute()
249// int second()
250//
251// Recall that fields inferior to the type's alignment will be set to their
252// minimum valid value.
253//
254// Example:
255//
256// absl::CivilDay d(2015, 6, 28);
257// // d.year() == 2015
258// // d.month() == 6
259// // d.day() == 28
260// // d.hour() == 0
261// // d.minute() == 0
262// // d.second() == 0
263//
264// CASE STUDY: Adding a month to January 31.
265//
266// One of the classic questions that arises when considering a civil time
267// library (or a date library or a date/time library) is this:
268// "What is the result of adding a month to January 31?"
269// This is an interesting question because it is unclear what is meant by a
270// "month", and several different answers are possible, depending on context:
271//
272// 1. March 3 (or 2 if a leap year), if "add a month" means to add a month to
273// the current month, and adjust the date to overflow the extra days into
274// March. In this case the result of "February 31" would be normalized as
275// within the civil-time library.
276// 2. February 28 (or 29 if a leap year), if "add a month" means to add a
277// month, and adjust the date while holding the resulting month constant.
278// In this case, the result of "February 31" would be truncated to the last
279// day in February.
280// 3. An error. The caller may get some error, an exception, an invalid date
281// object, or perhaps return `false`. This may make sense because there is
282// no single unambiguously correct answer to the question.
283//
284// Practically speaking, any answer that is not what the programmer intended
285// is the wrong answer.
286//
287// The Abseil time library avoids this problem by making it impossible to
288// ask ambiguous questions. All civil-time objects are aligned to a particular
289// civil-field boundary (such as aligned to a year, month, day, hour, minute,
290// or second), and arithmetic operates on the field to which the object is
291// aligned. This means that in order to "add a month" the object must first be
292// aligned to a month boundary, which is equivalent to the first day of that
293// month.
294//
295// Of course, there are ways to compute an answer the question at hand using
296// this Abseil time library, but they require the programmer to be explicit
297// about the answer they expect. To illustrate, let's see how to compute all
298// three of the above possible answers to the question of "Jan 31 plus 1
299// month":
300//
301// Example:
302//
303// const absl::CivilDay d(2015, 1, 31);
304//
305// // Answer 1:
306// // Add 1 to the month field in the constructor, and rely on normalization.
307// const auto normalized = absl::CivilDay(d.year(), d.month() + 1, d.day());
308// // normalized == 2015-03-03 (aka Feb 31)
309//
310// // Answer 2:
311// // Add 1 to month field, capping to the end of next month.
312// const auto next_month = absl::CivilMonth(d) + 1;
313// const auto last_day_of_next_month = absl::CivilDay(next_month + 1) - 1;
314// const auto capped = std::min(normalized, last_day_of_next_month);
315// // capped == 2015-02-28
316//
317// // Answer 3:
318// // Signal an error if the normalized answer is not in next month.
319// if (absl::CivilMonth(normalized) != next_month) {
320// // error, month overflow
321// }
322//
323using CivilSecond =
324 time_internal::cctz::detail::civil_time<time_internal::second_tag>;
325using CivilMinute =
326 time_internal::cctz::detail::civil_time<time_internal::minute_tag>;
327using CivilHour =
328 time_internal::cctz::detail::civil_time<time_internal::hour_tag>;
329using CivilDay =
330 time_internal::cctz::detail::civil_time<time_internal::day_tag>;
331using CivilMonth =
332 time_internal::cctz::detail::civil_time<time_internal::month_tag>;
333using CivilYear =
334 time_internal::cctz::detail::civil_time<time_internal::year_tag>;
335
336// civil_year_t
337//
338// Type alias of a civil-time year value. This type is guaranteed to (at least)
339// support any year value supported by `time_t`.
340//
341// Example:
342//
343// absl::CivilSecond cs = ...;
344// absl::civil_year_t y = cs.year();
345// cs = absl::CivilSecond(y, 1, 1, 0, 0, 0); // CivilSecond(CivilYear(cs))
346//
347using civil_year_t = time_internal::cctz::year_t;
348
349// civil_diff_t
350//
351// Type alias of the difference between two civil-time values.
352// This type is used to indicate arguments that are not
353// normalized (such as parameters to the civil-time constructors), the results
354// of civil-time subtraction, or the operand to civil-time addition.
355//
356// Example:
357//
358// absl::civil_diff_t n_sec = cs1 - cs2; // cs1 == cs2 + n_sec;
359//
360using civil_diff_t = time_internal::cctz::diff_t;
361
362// Weekday::monday, Weekday::tuesday, Weekday::wednesday, Weekday::thursday,
363// Weekday::friday, Weekday::saturday, Weekday::sunday
364//
365// The Weekday enum class represents the civil-time concept of a "weekday" with
366// members for all days of the week.
367//
368// absl::Weekday wd = absl::Weekday::thursday;
369//
370using Weekday = time_internal::cctz::weekday;
371
372// GetWeekday()
373//
374// Returns the absl::Weekday for the given (realigned) civil-time value.
375//
376// Example:
377//
378// absl::CivilDay a(2015, 8, 13);
379// absl::Weekday wd = absl::GetWeekday(a); // wd == absl::Weekday::thursday
380//
381inline Weekday GetWeekday(CivilSecond cs) {
382 return time_internal::cctz::get_weekday(cs);
383}
384
385// NextWeekday()
386// PrevWeekday()
387//
388// Returns the absl::CivilDay that strictly follows or precedes a given
389// absl::CivilDay, and that falls on the given absl::Weekday.
390//
391// Example, given the following month:
392//
393// August 2015
394// Su Mo Tu We Th Fr Sa
395// 1
396// 2 3 4 5 6 7 8
397// 9 10 11 12 13 14 15
398// 16 17 18 19 20 21 22
399// 23 24 25 26 27 28 29
400// 30 31
401//
402// absl::CivilDay a(2015, 8, 13);
403// // absl::GetWeekday(a) == absl::Weekday::thursday
404// absl::CivilDay b = absl::NextWeekday(a, absl::Weekday::thursday);
405// // b = 2015-08-20
406// absl::CivilDay c = absl::PrevWeekday(a, absl::Weekday::thursday);
407// // c = 2015-08-06
408//
409// absl::CivilDay d = ...
410// // Gets the following Thursday if d is not already Thursday
411// absl::CivilDay thurs1 = absl::NextWeekday(d - 1, absl::Weekday::thursday);
412// // Gets the previous Thursday if d is not already Thursday
413// absl::CivilDay thurs2 = absl::PrevWeekday(d + 1, absl::Weekday::thursday);
414//
415inline CivilDay NextWeekday(CivilDay cd, Weekday wd) {
416 return CivilDay(time_internal::cctz::next_weekday(cd, wd));
417}
418inline CivilDay PrevWeekday(CivilDay cd, Weekday wd) {
419 return CivilDay(time_internal::cctz::prev_weekday(cd, wd));
420}
421
422// GetYearDay()
423//
424// Returns the day-of-year for the given (realigned) civil-time value.
425//
426// Example:
427//
428// absl::CivilDay a(2015, 1, 1);
429// int yd_jan_1 = absl::GetYearDay(a); // yd_jan_1 = 1
430// absl::CivilDay b(2015, 12, 31);
431// int yd_dec_31 = absl::GetYearDay(b); // yd_dec_31 = 365
432//
433inline int GetYearDay(CivilSecond cs) {
434 return time_internal::cctz::get_yearday(cs);
435}
436
437// FormatCivilTime()
438//
439// Formats the given civil-time value into a string value of the following
440// format:
441//
442// Type | Format
443// ---------------------------------
444// CivilSecond | YYYY-MM-DDTHH:MM:SS
445// CivilMinute | YYYY-MM-DDTHH:MM
446// CivilHour | YYYY-MM-DDTHH
447// CivilDay | YYYY-MM-DD
448// CivilMonth | YYYY-MM
449// CivilYear | YYYY
450//
451// Example:
452//
453// absl::CivilDay d = absl::CivilDay(1969, 7, 20);
454// std::string day_string = absl::FormatCivilTime(d); // "1969-07-20"
455//
456std::string FormatCivilTime(CivilSecond c);
457std::string FormatCivilTime(CivilMinute c);
458std::string FormatCivilTime(CivilHour c);
459std::string FormatCivilTime(CivilDay c);
460std::string FormatCivilTime(CivilMonth c);
461std::string FormatCivilTime(CivilYear c);
462
463// absl::ParseCivilTime()
464//
465// Parses a civil-time value from the specified `absl::string_view` into the
466// passed output parameter. Returns `true` upon successful parsing.
467//
468// The expected form of the input string is as follows:
469//
470// Type | Format
471// ---------------------------------
472// CivilSecond | YYYY-MM-DDTHH:MM:SS
473// CivilMinute | YYYY-MM-DDTHH:MM
474// CivilHour | YYYY-MM-DDTHH
475// CivilDay | YYYY-MM-DD
476// CivilMonth | YYYY-MM
477// CivilYear | YYYY
478//
479// Example:
480//
481// absl::CivilDay d;
482// bool ok = absl::ParseCivilTime("2018-01-02", &d); // OK
483//
484// Note that parsing will fail if the string's format does not match the
485// expected type exactly. `ParseLenientCivilTime()` below is more lenient.
486//
487bool ParseCivilTime(absl::string_view s, CivilSecond* c);
488bool ParseCivilTime(absl::string_view s, CivilMinute* c);
489bool ParseCivilTime(absl::string_view s, CivilHour* c);
490bool ParseCivilTime(absl::string_view s, CivilDay* c);
491bool ParseCivilTime(absl::string_view s, CivilMonth* c);
492bool ParseCivilTime(absl::string_view s, CivilYear* c);
493
494// ParseLenientCivilTime()
495//
496// Parses any of the formats accepted by `absl::ParseCivilTime()`, but is more
497// lenient if the format of the string does not exactly match the associated
498// type.
499//
500// Example:
501//
502// absl::CivilDay d;
503// bool ok = absl::ParseLenientCivilTime("1969-07-20", &d); // OK
504// ok = absl::ParseLenientCivilTime("1969-07-20T10", &d); // OK: T10 floored
505// ok = absl::ParseLenientCivilTime("1969-07", &d); // OK: day defaults to 1
506//
507bool ParseLenientCivilTime(absl::string_view s, CivilSecond* c);
508bool ParseLenientCivilTime(absl::string_view s, CivilMinute* c);
509bool ParseLenientCivilTime(absl::string_view s, CivilHour* c);
510bool ParseLenientCivilTime(absl::string_view s, CivilDay* c);
511bool ParseLenientCivilTime(absl::string_view s, CivilMonth* c);
512bool ParseLenientCivilTime(absl::string_view s, CivilYear* c);
513
514namespace time_internal { // For functions found via ADL on civil-time tags.
515
516// Streaming Operators
517//
518// Each civil-time type may be sent to an output stream using operator<<().
519// The result matches the string produced by `FormatCivilTime()`.
520//
521// Example:
522//
523// absl::CivilDay d = absl::CivilDay(1969, 7, 20);
524// std::cout << "Date is: " << d << "\n";
525//
526std::ostream& operator<<(std::ostream& os, CivilYear y);
527std::ostream& operator<<(std::ostream& os, CivilMonth m);
528std::ostream& operator<<(std::ostream& os, CivilDay d);
529std::ostream& operator<<(std::ostream& os, CivilHour h);
530std::ostream& operator<<(std::ostream& os, CivilMinute m);
531std::ostream& operator<<(std::ostream& os, CivilSecond s);
532
533} // namespace time_internal
534
535ABSL_NAMESPACE_END
536} // namespace absl
537
538#endif // ABSL_TIME_CIVIL_TIME_H_
539

source code of include/absl/time/civil_time.h