/*!

Facilities for dealing with inexact dates and times.

# Overview

The essential types in this module are:

* [`Date`] is a specific day in the Gregorian calendar.

* [`Time`] is a specific wall clock time.

* [`DateTime`] is a combination of a day and a time.

Moreover, the [`date`](date()) and [`time`](time()) free functions can be used

to conveniently create values of any of three types above:

```

use jiff::civil::{date, time};

assert_eq!(date(2024, 7, 31).to_string(), "2024-07-31");

assert_eq!(time(15, 20, 0, 123).to_string(), "15:20:00.000000123");

assert_eq!(

    date(2024, 7, 31).at(15, 20, 0, 123).to_string(),

    "2024-07-31T15:20:00.000000123",

);

assert_eq!(

    time(15, 20, 0, 123).on(2024, 7, 31).to_string(),

    "2024-07-31T15:20:00.000000123",

);

```

# What is "civil" time?

A civil datetime is a calendar date and a clock time. It also goes by the

names "naive," "local" or "plain." The most important thing to understand

about civil time is that it does not correspond to a precise instant in

time. This is in contrast to types like [`Timestamp`](crate::Timestamp) and

[`Zoned`](crate::Zoned), which _do_ correspond to a precise instant in time (to

nanosecond precision).

Because a civil datetime _never_ has a time zone associated with it, and

because some time zones have transitions that skip or repeat clock times, it

follows that not all civil datetimes precisely map to a single instant in time.

For example, `2024-03-10 02:30` never existed on a clock in `America/New_York`

because the 2 o'clock hour was skipped when the clocks were "moved forward"

for daylight saving time. Conversely, `2024-11-03 01:30` occurred twice in

`America/New_York` because the 1 o'clock hour was repeated when clocks were

"moved backward" for daylight saving time. (When time is skipped, it's called a

"gap." When time is repeated, it's called a "fold.")

In contrast, an instant in time (that is, `Timestamp` or `Zoned`) can _always_

be converted to a civil datetime. And, when a civil datetime is combined

with its time zone identifier _and_ its offset, the resulting machine readable

string is unambiguous 100% of the time:

```

use jiff::{civil::date, tz::TimeZone};

let tz = TimeZone::get("America/New_York")?;

let dt = date(2024, 11, 3).at(1, 30, 0, 0);

// It's ambiguous, so asking for an unambiguous instant presents an error!

assert!(tz.to_ambiguous_zoned(dt).unambiguous().is_err());

// Gives you the earlier time in a fold, i.e., before DST ends:

assert_eq!(

    tz.to_ambiguous_zoned(dt).earlier()?.to_string(),

    "2024-11-03T01:30:00-04:00[America/New_York]",

);

// Gives you the later time in a fold, i.e., after DST ends.

// Notice the offset change from the previous example!

assert_eq!(

    tz.to_ambiguous_zoned(dt).later()?.to_string(),

    "2024-11-03T01:30:00-05:00[America/New_York]",

);

// "Just give me something reasonable"

assert_eq!(

    tz.to_ambiguous_zoned(dt).compatible()?.to_string(),

    "2024-11-03T01:30:00-04:00[America/New_York]",

);

# Ok::<(), Box<dyn std::error::Error>>(())

```

# When should I use civil time?

Here is a likely non-exhaustive list of reasons why you might want to use

civil time:

* When you want or need to deal with calendar and clock units as an

intermediate step before and/or after associating it with a time zone. For

example, perhaps you need to parse strings like `2000-01-01T00:00:00` from a

CSV file that have no time zone or offset information, but the time zone is

implied through some out-of-band mechanism.

* When time zone is actually irrelevant. For example, a fitness tracking app

that reminds you to work-out at 6am local time, regardless of which time zone

you're in.

* When you need to perform arithmetic that deliberately ignores daylight

saving time.

* When interacting with legacy systems or systems that specifically do not

support time zones.

*/

pub use self::{

    date::{Date, DateArithmetic, DateDifference, DateSeries, DateWith},

    datetime::{

        DateTime, DateTimeArithmetic, DateTimeDifference, DateTimeRound,

        DateTimeSeries, DateTimeWith,

    },

    iso_week_date::ISOWeekDate,

    time::{

        Time, TimeArithmetic, TimeDifference, TimeRound, TimeSeries, TimeWith,

    },

    weekday::{Weekday, WeekdaysForward, WeekdaysReverse},

};

mod date;

mod datetime;

mod iso_week_date;

mod time;

mod weekday;

/// The era corresponding to a particular year.

///

/// The BCE era corresponds to years less than or equal to `0`, while the CE

/// era corresponds to years greater than `0`.

///

/// In particular, this crate allows years to be negative and also to be `0`,

/// which is contrary to the common practice of excluding the year `0` when

/// writing dates for the Gregorian calendar. Moreover, common practice eschews

/// negative years in favor of labeling a year with an era notation. That is,

/// the year `1 BCE` is year `0` in this crate. The year `2 BCE` is the year

/// `-1` in this crate.

///

/// To get the year in its era format, use [`Date::era_year`].

#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]

pub enum Era {

    /// The "before common era" era.

    ///

    /// This corresponds to all years less than or equal to `0`.

    ///

    /// This is precisely equivalent to the "BC" or "before Christ" era.

    BCE,

    /// The "common era" era.

    ///

    /// This corresponds to all years greater than `0`.

    ///

    /// This is precisely equivalent to the "AD" or "anno Domini" or "in the

    /// year of the Lord" era.

    CE,

}

/// Creates a new `DateTime` value in a `const` context.

///

/// This is a convenience free function for [`DateTime::constant`]. It is

/// intended to provide a terse syntax for constructing `DateTime` values from

/// parameters that are known to be valid.

///

/// # Panics

///

/// This routine panics when [`DateTime::new`] would return an error. That

/// is, when the given components do not correspond to a valid datetime.

/// Namely, all of the following must be true:

///

/// * The year must be in the range `-9999..=9999`.

/// * The month must be in the range `1..=12`.

/// * The day must be at least `1` and must be at most the number of days

/// in the corresponding month. So for example, `2024-02-29` is valid but

/// `2023-02-29` is not.

/// * `0 <= hour <= 23`

/// * `0 <= minute <= 59`

/// * `0 <= second <= 59`

/// * `0 <= subsec_nanosecond <= 999,999,999`

///

/// Similarly, when used in a const context, invalid parameters will prevent

/// your Rust program from compiling.

///

/// # Example

///

/// ```

/// use jiff::civil::DateTime;

///

/// let d = DateTime::constant(2024, 2, 29, 21, 30, 5, 123_456_789);

/// assert_eq!(d.date().year(), 2024);

/// assert_eq!(d.date().month(), 2);

/// assert_eq!(d.date().day(), 29);

/// assert_eq!(d.time().hour(), 21);

/// assert_eq!(d.time().minute(), 30);

/// assert_eq!(d.time().second(), 5);

/// assert_eq!(d.time().millisecond(), 123);

/// assert_eq!(d.time().microsecond(), 456);

/// assert_eq!(d.time().nanosecond(), 789);

/// ```

#[inline]

pub const fn datetime(

    year: i16,

    month: i8,

    day: i8,

    hour: i8,

    minute: i8,

    second: i8,

    subsec_nanosecond: i32,

) -> DateTime {

    DateTime::constant(

        year,

        month,

        day,

        hour,

        minute,

        second,

        subsec_nanosecond,

    )

}

/// Creates a new `Date` value in a `const` context.

///

/// This is a convenience free function for [`Date::constant`]. It is intended

/// to provide a terse syntax for constructing `Date` values from parameters

/// that are known to be valid.

///

/// # Panics

///

/// This routine panics when [`Date::new`] would return an error. That is,

/// when the given year-month-day does not correspond to a valid date.

/// Namely, all of the following must be true:

///

/// * The year must be in the range `-9999..=9999`.

/// * The month must be in the range `1..=12`.

/// * The day must be at least `1` and must be at most the number of days

/// in the corresponding month. So for example, `2024-02-29` is valid but

/// `2023-02-29` is not.

///

/// Similarly, when used in a const context, invalid parameters will prevent

/// your Rust program from compiling.

///

/// # Example

///

/// ```

/// use jiff::civil::date;

///

/// let d = date(2024, 2, 29);

/// assert_eq!(d.year(), 2024);

/// assert_eq!(d.month(), 2);

/// assert_eq!(d.day(), 29);

/// ```

#[inline]

pub const fn date(year: i16, month: i8, day: i8) -> Date {

    Date::constant(year, month, day)

}

/// Creates a new `Time` value in a `const` context.

///

/// This is a convenience free function for [`Time::constant`]. It is intended

/// to provide a terse syntax for constructing `Time` values from parameters

/// that are known to be valid.

///

/// # Panics

///

/// This panics if the given values do not correspond to a valid `Time`.

/// All of the following conditions must be true:

///

/// * `0 <= hour <= 23`

/// * `0 <= minute <= 59`

/// * `0 <= second <= 59`

/// * `0 <= subsec_nanosecond <= 999,999,999`

///

/// Similarly, when used in a const context, invalid parameters will

/// prevent your Rust program from compiling.

///

/// # Example

///

/// This shows an example of a valid time in a `const` context:

///

/// ```

/// use jiff::civil::Time;

///

/// const BEDTIME: Time = Time::constant(21, 30, 5, 123_456_789);

/// assert_eq!(BEDTIME.hour(), 21);

/// assert_eq!(BEDTIME.minute(), 30);

/// assert_eq!(BEDTIME.second(), 5);

/// assert_eq!(BEDTIME.millisecond(), 123);

/// assert_eq!(BEDTIME.microsecond(), 456);

/// assert_eq!(BEDTIME.nanosecond(), 789);

/// assert_eq!(BEDTIME.subsec_nanosecond(), 123_456_789);

/// ```

#[inline]

pub const fn time(

    hour: i8,

    minute: i8,

    second: i8,

    subsec_nanosecond: i32,

) -> Time {

    Time::constant(hour, minute, second, subsec_nanosecond)

}