@spec add(
  Calendar.datetime(),
  integer(),
  :day | :hour | :minute | System.time_unit(),
  Calendar.time_zone_database()
) :: t()

Adds a specified amount of time to a DateTime.

Accepts an amount_to_add in any unit. unit can be :day, :hour, :minute, :second or any subsecond precision from System.time_unit/0. It defaults to :second. Negative values will move backwards in time.

This function always consider the unit to be computed according to the Calendar.ISO.

This function uses relies on a contiguous representation of time, ignoring the wall time and timezone changes. For example, if you add one day when there are summer time/daylight saving time changes, it will also change the time forward or backward by one hour, so the ellapsed time is precisely 24 hours. Similarly, adding just a few seconds to a datetime just before "spring forward" can cause wall time to increase by more than an hour.

While this means this function is precise in terms of ellapsed time, its result may be misleading in certain use cases. For example, if a user requests a meeting to happen every day at 15:00 and you use this function to compute all future meetings by adding day after day, this function may change the meeting time to 14:00 or 16:00 if there are changes to the current timezone. Computing of recurring datetimes is not currently supported in Elixir's standard library but it is available by third-party libraries.

Examples

iex> dt = DateTime.from_naive!(~N[2018-11-15 10:00:00], "Europe/Copenhagen", FakeTimeZoneDatabase)
iex> dt |> DateTime.add(3600, :second, FakeTimeZoneDatabase)
#DateTime<2018-11-15 11:00:00+01:00 CET Europe/Copenhagen>

iex> DateTime.add(~U[2018-11-15 10:00:00Z], 3600, :second)
~U[2018-11-15 11:00:00Z]

When adding 3 seconds just before "spring forward" we go from 1:59:59 to 3:00:02:

iex> dt = DateTime.from_naive!(~N[2019-03-31 01:59:59.123], "Europe/Copenhagen", FakeTimeZoneDatabase)
iex> dt |> DateTime.add(3, :second, FakeTimeZoneDatabase)
#DateTime<2019-03-31 03:00:02.123+02:00 CEST Europe/Copenhagen>

When adding 1 day during "spring forward", the hour also changes:

iex> dt = DateTime.from_naive!(~N[2019-03-31 01:00:00], "Europe/Copenhagen", FakeTimeZoneDatabase)
iex> dt |> DateTime.add(1, :day, FakeTimeZoneDatabase)
#DateTime<2019-04-01 02:00:00+02:00 CEST Europe/Copenhagen>

@spec compare(Calendar.datetime(), Calendar.datetime()) :: :lt | :eq | :gt

Compares two datetime structs.

Returns :gt if the first datetime is later than the second and :lt for vice versa. If the two datetimes are equal :eq is returned.

Note that both UTC and Standard offsets will be taken into account when comparison is done.

Examples

iex> dt1 = %DateTime{year: 2000, month: 2, day: 29, zone_abbr: "AMT",
...>                 hour: 23, minute: 0, second: 7, microsecond: {0, 0},
...>                 utc_offset: -14400, std_offset: 0, time_zone: "America/Manaus"}
iex> dt2 = %DateTime{year: 2000, month: 2, day: 29, zone_abbr: "CET",
...>                 hour: 23, minute: 0, second: 7, microsecond: {0, 0},
...>                 utc_offset: 3600, std_offset: 0, time_zone: "Europe/Warsaw"}
iex> DateTime.compare(dt1, dt2)
:gt

@spec convert(Calendar.datetime(), Calendar.calendar()) ::
  {:ok, t()} | {:error, :incompatible_calendars}

Converts a given datetime from one calendar to another.

If it is not possible to convert unambiguously between the calendars (see Calendar.compatible_calendars?/2), an {:error, :incompatible_calendars} tuple is returned.

Examples

Imagine someone implements Calendar.Holocene, a calendar based on the Gregorian calendar that adds exactly 10,000 years to the current Gregorian year:

iex> dt1 = %DateTime{year: 2000, month: 2, day: 29, zone_abbr: "AMT",
...>                 hour: 23, minute: 0, second: 7, microsecond: {0, 0},
...>                 utc_offset: -14400, std_offset: 0, time_zone: "America/Manaus"}
iex> DateTime.convert(dt1, Calendar.Holocene)
{:ok, %DateTime{calendar: Calendar.Holocene, day: 29, hour: 23,
                microsecond: {0, 0}, minute: 0, month: 2, second: 7, std_offset: 0,
                time_zone: "America/Manaus", utc_offset: -14400, year: 12000,
                zone_abbr: "AMT"}}

@spec convert!(Calendar.datetime(), Calendar.calendar()) :: t()

Converts a given datetime from one calendar to another.

If it is not possible to convert unambiguously between the calendars (see Calendar.compatible_calendars?/2), an ArgumentError is raised.

Examples

Imagine someone implements Calendar.Holocene, a calendar based on the Gregorian calendar that adds exactly 10,000 years to the current Gregorian year:

iex> dt1 = %DateTime{year: 2000, month: 2, day: 29, zone_abbr: "AMT",
...>                 hour: 23, minute: 0, second: 7, microsecond: {0, 0},
...>                 utc_offset: -14400, std_offset: 0, time_zone: "America/Manaus"}
iex> DateTime.convert!(dt1, Calendar.Holocene)
%DateTime{calendar: Calendar.Holocene, day: 29, hour: 23,
          microsecond: {0, 0}, minute: 0, month: 2, second: 7, std_offset: 0,
          time_zone: "America/Manaus", utc_offset: -14400, year: 12000,
          zone_abbr: "AMT"}

@spec diff(
  Calendar.datetime(),
  Calendar.datetime(),
  :day | :hour | :minute | System.time_unit()
) :: integer()

Subtracts datetime2 from datetime1.

The answer can be returned in any :day, :hour, :minute, or any unit available from System.time_unit/0. The unit is measured according to Calendar.ISO and defaults to :second.

Fractional results are not supported and are truncated.

Examples

iex> dt1 = %DateTime{year: 2000, month: 2, day: 29, zone_abbr: "AMT",
...>                 hour: 23, minute: 0, second: 7, microsecond: {0, 0},
...>                 utc_offset: -14400, std_offset: 0, time_zone: "America/Manaus"}
iex> dt2 = %DateTime{year: 2000, month: 2, day: 29, zone_abbr: "CET",
...>                 hour: 23, minute: 0, second: 7, microsecond: {0, 0},
...>                 utc_offset: 3600, std_offset: 0, time_zone: "Europe/Warsaw"}
iex> DateTime.diff(dt1, dt2)
18000
iex> DateTime.diff(dt2, dt1)
-18000
iex> DateTime.diff(dt1, dt2, :hour)
5
iex> DateTime.diff(dt2, dt1, :hour)
-5

@spec from_gregorian_seconds(integer(), Calendar.microsecond(), Calendar.calendar()) ::
  t()

Converts a number of gregorian seconds to a DateTime struct.

The returned DateTime will have UTC timezone, if you want other timezone, please use DateTime.shift_zone/3.

Examples

iex> DateTime.from_gregorian_seconds(1)
~U[0000-01-01 00:00:01Z]
iex> DateTime.from_gregorian_seconds(63_755_511_991, {5000, 3})
~U[2020-05-01 00:26:31.005Z]
iex> DateTime.from_gregorian_seconds(-1)
~U[-0001-12-31 23:59:59Z]

Parses the extended "Date and time of day" format described by ISO 8601:2019.

Since ISO 8601 does not include the proper time zone, the given string will be converted to UTC and its offset in seconds will be returned as part of this function. Therefore offset information must be present in the string.

As specified in the standard, the separator "T" may be omitted if desired as there is no ambiguity within this function.

Note leap seconds are not supported by the built-in Calendar.ISO.

Examples

iex> {:ok, datetime, 0} = DateTime.from_iso8601("2015-01-23T23:50:07Z")
iex> datetime
~U[2015-01-23 23:50:07Z]

iex> {:ok, datetime, 9000} = DateTime.from_iso8601("2015-01-23T23:50:07.123+02:30")
iex> datetime
~U[2015-01-23 21:20:07.123Z]

iex> {:ok, datetime, 9000} = DateTime.from_iso8601("2015-01-23T23:50:07,123+02:30")
iex> datetime
~U[2015-01-23 21:20:07.123Z]

iex> {:ok, datetime, 0} = DateTime.from_iso8601("-2015-01-23T23:50:07Z")
iex> datetime
~U[-2015-01-23 23:50:07Z]

iex> {:ok, datetime, 9000} = DateTime.from_iso8601("-2015-01-23T23:50:07,123+02:30")
iex> datetime
~U[-2015-01-23 21:20:07.123Z]

iex> {:ok, datetime, 9000} = DateTime.from_iso8601("20150123T235007.123+0230", :basic)
iex> datetime
~U[2015-01-23 21:20:07.123Z]

iex> DateTime.from_iso8601("2015-01-23P23:50:07")
{:error, :invalid_format}
iex> DateTime.from_iso8601("2015-01-23T23:50:07")
{:error, :missing_offset}
iex> DateTime.from_iso8601("2015-01-23 23:50:61")
{:error, :invalid_time}
iex> DateTime.from_iso8601("2015-01-32 23:50:07")
{:error, :invalid_date}
iex> DateTime.from_iso8601("2015-01-23T23:50:07.123-00:00")
{:error, :invalid_format}

@spec from_iso8601(String.t(), Calendar.calendar(), :extended | :basic) ::
  {:ok, t(), Calendar.utc_offset()} | {:error, atom()}

Converts to ISO8601 specifying both a calendar and a mode.

See from_iso8601/2 for more information.

Examples

iex> {:ok, datetime, 9000} = DateTime.from_iso8601("2015-01-23T23:50:07,123+02:30", Calendar.ISO, :extended)
iex> datetime
~U[2015-01-23 21:20:07.123Z]

iex> {:ok, datetime, 9000} = DateTime.from_iso8601("20150123T235007.123+0230", Calendar.ISO, :basic)
iex> datetime
~U[2015-01-23 21:20:07.123Z]

@spec from_naive(
  Calendar.naive_datetime(),
  Calendar.time_zone(),
  Calendar.time_zone_database()
) ::
  {:ok, t()}
  | {:ambiguous, first_datetime :: t(), second_datetime :: t()}
  | {:gap, t(), t()}
  | {:error,
     :incompatible_calendars
     | :time_zone_not_found
     | :utc_only_time_zone_database}

Converts the given NaiveDateTime to DateTime.

It expects a time zone to put the NaiveDateTime in. If the time zone is "Etc/UTC", it always succeeds. Otherwise, the NaiveDateTime is checked against the time zone database given as time_zone_database. See the "Time zone database" section in the module documentation.

Examples

iex> DateTime.from_naive(~N[2016-05-24 13:26:08.003], "Etc/UTC")
{:ok, ~U[2016-05-24 13:26:08.003Z]}

When the datetime is ambiguous - for instance during changing from summer to winter time - the two possible valid datetimes are returned in a tuple. The first datetime is also the one which comes first chronologically, while the second one comes last.

iex> {:ambiguous, first_dt, second_dt} = DateTime.from_naive(~N[2018-10-28 02:30:00], "Europe/Copenhagen", FakeTimeZoneDatabase)
iex> first_dt
#DateTime<2018-10-28 02:30:00+02:00 CEST Europe/Copenhagen>
iex> second_dt
#DateTime<2018-10-28 02:30:00+01:00 CET Europe/Copenhagen>

When there is a gap in wall time - for instance in spring when the clocks are turned forward - the latest valid datetime just before the gap and the first valid datetime just after the gap.

iex> {:gap, just_before, just_after} = DateTime.from_naive(~N[2019-03-31 02:30:00], "Europe/Copenhagen", FakeTimeZoneDatabase)
iex> just_before
#DateTime<2019-03-31 01:59:59.999999+01:00 CET Europe/Copenhagen>
iex> just_after
#DateTime<2019-03-31 03:00:00+02:00 CEST Europe/Copenhagen>

Most of the time there is one, and just one, valid datetime for a certain date and time in a certain time zone.

iex> {:ok, datetime} = DateTime.from_naive(~N[2018-07-28 12:30:00], "Europe/Copenhagen", FakeTimeZoneDatabase)
iex> datetime
#DateTime<2018-07-28 12:30:00+02:00 CEST Europe/Copenhagen>

This function accepts any map or struct that contains at least the same fields as a NaiveDateTime struct. The most common example of that is a DateTime. In this case the information about the time zone of that DateTime is completely ignored. This is the same principle as passing a DateTime to Date.to_iso8601/2. Date.to_iso8601/2 extracts only the date-specific fields (calendar, year, month and day) of the given structure and ignores all others.

This way if you have a DateTime in one time zone, you can get the same wall time in another time zone. For instance if you have 2018-08-24 10:00:00 in Copenhagen and want a DateTime for 2018-08-24 10:00:00 in UTC you can do:

iex> cph_datetime = DateTime.from_naive!(~N[2018-08-24 10:00:00], "Europe/Copenhagen", FakeTimeZoneDatabase)
iex> {:ok, utc_datetime} = DateTime.from_naive(cph_datetime, "Etc/UTC", FakeTimeZoneDatabase)
iex> utc_datetime
~U[2018-08-24 10:00:00Z]

If instead you want a DateTime for the same point time in a different time zone see the DateTime.shift_zone/3 function which would convert 2018-08-24 10:00:00 in Copenhagen to 2018-08-24 08:00:00 in UTC.

@spec from_naive!(
  NaiveDateTime.t(),
  Calendar.time_zone(),
  Calendar.time_zone_database()
) :: t()

Converts the given NaiveDateTime to DateTime.

It expects a time zone to put the NaiveDateTime in. If the time zone is "Etc/UTC", it always succeeds. Otherwise, the NaiveDateTime is checked against the time zone database given as time_zone_database. See the "Time zone database" section in the module documentation.

Examples

iex> DateTime.from_naive!(~N[2016-05-24 13:26:08.003], "Etc/UTC")
~U[2016-05-24 13:26:08.003Z]

iex> DateTime.from_naive!(~N[2018-05-24 13:26:08.003], "Europe/Copenhagen", FakeTimeZoneDatabase)
#DateTime<2018-05-24 13:26:08.003+02:00 CEST Europe/Copenhagen>

@spec from_unix(integer(), :native | System.time_unit(), Calendar.calendar()) ::
  {:ok, t()} | {:error, atom()}

Converts the given Unix time to DateTime.

The integer can be given in different unit according to System.convert_time_unit/3 and it will be converted to microseconds internally. Up to 253402300799 seconds is supported.

Unix times are always in UTC and therefore the DateTime will be returned in UTC.

Examples

iex> {:ok, datetime} = DateTime.from_unix(1_464_096_368)
iex> datetime
~U[2016-05-24 13:26:08Z]

iex> {:ok, datetime} = DateTime.from_unix(1_432_560_368_868_569, :microsecond)
iex> datetime
~U[2015-05-25 13:26:08.868569Z]

iex> {:ok, datetime} = DateTime.from_unix(253_402_300_799)
iex> datetime
~U[9999-12-31 23:59:59Z]

iex> {:error, :invalid_unix_time} = DateTime.from_unix(253_402_300_800)

The unit can also be an integer as in System.time_unit/0:

iex> {:ok, datetime} = DateTime.from_unix(143_256_036_886_856, 1024)
iex> datetime
~U[6403-03-17 07:05:22.320312Z]

Negative Unix times are supported up to -377705116800 seconds:

iex> {:ok, datetime} = DateTime.from_unix(-377_705_116_800)
iex> datetime
~U[-9999-01-01 00:00:00Z]

iex> {:error, :invalid_unix_time} = DateTime.from_unix(-377_705_116_801)

@spec from_unix!(integer(), :native | System.time_unit(), Calendar.calendar()) :: t()

Converts the given Unix time to DateTime.

The integer can be given in different unit according to System.convert_time_unit/3 and it will be converted to microseconds internally.

Unix times are always in UTC and therefore the DateTime will be returned in UTC.

Examples

# An easy way to get the Unix epoch is passing 0 to this function
iex> DateTime.from_unix!(0)
~U[1970-01-01 00:00:00Z]

iex> DateTime.from_unix!(1_464_096_368)
~U[2016-05-24 13:26:08Z]

iex> DateTime.from_unix!(1_432_560_368_868_569, :microsecond)
~U[2015-05-25 13:26:08.868569Z]

iex> DateTime.from_unix!(143_256_036_886_856, 1024)
~U[6403-03-17 07:05:22.320312Z]

@spec new(Date.t(), Time.t(), Calendar.time_zone(), Calendar.time_zone_database()) ::
  {:ok, t()}
  | {:ambiguous, first_datetime :: t(), second_datetime :: t()}
  | {:gap, t(), t()}
  | {:error,
     :incompatible_calendars
     | :time_zone_not_found
     | :utc_only_time_zone_database}

Builds a datetime from date and time structs.

It expects a time zone to put the DateTime in. If the time zone is not passed it will default to "Etc/UTC", which always succeeds. Otherwise, the DateTime is checked against the time zone database given as time_zone_database. See the "Time zone database" section in the module documentation.

Examples

iex> DateTime.new(~D[2016-05-24], ~T[13:26:08.003], "Etc/UTC")
{:ok, ~U[2016-05-24 13:26:08.003Z]}

When the datetime is ambiguous - for instance during changing from summer to winter time - the two possible valid datetimes are returned in a tuple. The first datetime is also the one which comes first chronologically, while the second one comes last.

iex> {:ambiguous, first_dt, second_dt} = DateTime.new(~D[2018-10-28], ~T[02:30:00], "Europe/Copenhagen", FakeTimeZoneDatabase)
iex> first_dt
#DateTime<2018-10-28 02:30:00+02:00 CEST Europe/Copenhagen>
iex> second_dt
#DateTime<2018-10-28 02:30:00+01:00 CET Europe/Copenhagen>

When there is a gap in wall time - for instance in spring when the clocks are turned forward - the latest valid datetime just before the gap and the first valid datetime just after the gap.

iex> {:gap, just_before, just_after} = DateTime.new(~D[2019-03-31], ~T[02:30:00], "Europe/Copenhagen", FakeTimeZoneDatabase)
iex> just_before
#DateTime<2019-03-31 01:59:59.999999+01:00 CET Europe/Copenhagen>
iex> just_after
#DateTime<2019-03-31 03:00:00+02:00 CEST Europe/Copenhagen>

Most of the time there is one, and just one, valid datetime for a certain date and time in a certain time zone.

iex> {:ok, datetime} = DateTime.new(~D[2018-07-28], ~T[12:30:00], "Europe/Copenhagen", FakeTimeZoneDatabase)
iex> datetime
#DateTime<2018-07-28 12:30:00+02:00 CEST Europe/Copenhagen>

@spec new!(Date.t(), Time.t(), Calendar.time_zone(), Calendar.time_zone_database()) ::
  t()

Builds a datetime from date and time structs, raising on errors.

It expects a time zone to put the DateTime in. If the time zone is not passed it will default to "Etc/UTC", which always succeeds. Otherwise, the DateTime is checked against the time zone database given as time_zone_database. See the "Time zone database" section in the module documentation.

Examples

iex> DateTime.new!(~D[2016-05-24], ~T[13:26:08.003], "Etc/UTC")
~U[2016-05-24 13:26:08.003Z]

When the datetime is ambiguous - for instance during changing from summer to winter time - an error will be raised.

iex> DateTime.new!(~D[2018-10-28], ~T[02:30:00], "Europe/Copenhagen", FakeTimeZoneDatabase)
** (ArgumentError) cannot build datetime with ~D[2018-10-28] and ~T[02:30:00] because such instant is ambiguous in time zone Europe/Copenhagen as there is an overlap between #DateTime<2018-10-28 02:30:00+02:00 CEST Europe/Copenhagen> and #DateTime<2018-10-28 02:30:00+01:00 CET Europe/Copenhagen>

When there is a gap in wall time - for instance in spring when the clocks are turned forward - an error will be raised.

iex> DateTime.new!(~D[2019-03-31], ~T[02:30:00], "Europe/Copenhagen", FakeTimeZoneDatabase)
** (ArgumentError) cannot build datetime with ~D[2019-03-31] and ~T[02:30:00] because such instant does not exist in time zone Europe/Copenhagen as there is a gap between #DateTime<2019-03-31 01:59:59.999999+01:00 CET Europe/Copenhagen> and #DateTime<2019-03-31 03:00:00+02:00 CEST Europe/Copenhagen>

Most of the time there is one, and just one, valid datetime for a certain date and time in a certain time zone.

iex> datetime = DateTime.new!(~D[2018-07-28], ~T[12:30:00], "Europe/Copenhagen", FakeTimeZoneDatabase)
iex> datetime
#DateTime<2018-07-28 12:30:00+02:00 CEST Europe/Copenhagen>

@spec now(Calendar.time_zone(), Calendar.time_zone_database()) ::
  {:ok, t()} | {:error, :time_zone_not_found | :utc_only_time_zone_database}

Returns the current datetime in the provided time zone.

By default, it uses the default time_zone returned by Calendar.get_time_zone_database/0, which defaults to Calendar.UTCOnlyTimeZoneDatabase which only handles "Etc/UTC" datetimes. Other time zone databases can be passed as argument or set globally. See the "Time zone database" section in the module docs.

Examples

iex> {:ok, datetime} = DateTime.now("Etc/UTC")
iex> datetime.time_zone
"Etc/UTC"

iex> DateTime.now("Europe/Copenhagen")
{:error, :utc_only_time_zone_database}

iex> DateTime.now("bad timezone", FakeTimeZoneDatabase)
{:error, :time_zone_not_found}

@spec now!(Calendar.time_zone(), Calendar.time_zone_database()) :: t()

Returns the current datetime in the provided time zone or raises on errors

See now/2 for more information.

Examples

iex> datetime = DateTime.now!("Etc/UTC")
iex> datetime.time_zone
"Etc/UTC"

iex> DateTime.now!("Europe/Copenhagen")
** (ArgumentError) cannot get current datetime in "Europe/Copenhagen" time zone, reason: :utc_only_time_zone_database

iex> DateTime.now!("bad timezone", FakeTimeZoneDatabase)
** (ArgumentError) cannot get current datetime in "bad timezone" time zone, reason: :time_zone_not_found

@spec shift_zone(t(), Calendar.time_zone(), Calendar.time_zone_database()) ::
  {:ok, t()} | {:error, :time_zone_not_found | :utc_only_time_zone_database}

Changes the time zone of a DateTime.

Returns a DateTime for the same point in time, but instead at the time zone provided. It assumes that DateTime is valid and exists in the given time zone and calendar.

By default, it uses the default time zone database returned by Calendar.get_time_zone_database/0, which defaults to Calendar.UTCOnlyTimeZoneDatabase which only handles "Etc/UTC" datetimes. Other time zone databases can be passed as argument or set globally. See the "Time zone database" section in the module docs.

Examples

iex> {:ok, pacific_datetime} = DateTime.shift_zone(~U[2018-07-16 10:00:00Z], "America/Los_Angeles", FakeTimeZoneDatabase)
iex> pacific_datetime
#DateTime<2018-07-16 03:00:00-07:00 PDT America/Los_Angeles>

iex> DateTime.shift_zone(~U[2018-07-16 10:00:00Z], "bad timezone", FakeTimeZoneDatabase)
{:error, :time_zone_not_found}

@spec shift_zone!(t(), Calendar.time_zone(), Calendar.time_zone_database()) :: t()

Changes the time zone of a DateTime or raises on errors.

See shift_zone/3 for more information.

Examples

iex> DateTime.shift_zone!(~U[2018-07-16 10:00:00Z], "America/Los_Angeles", FakeTimeZoneDatabase)
#DateTime<2018-07-16 03:00:00-07:00 PDT America/Los_Angeles>

iex> DateTime.shift_zone!(~U[2018-07-16 10:00:00Z], "bad timezone", FakeTimeZoneDatabase)
** (ArgumentError) cannot shift ~U[2018-07-16 10:00:00Z] to "bad timezone" time zone, reason: :time_zone_not_found

@spec to_date(Calendar.datetime()) :: Date.t()

Converts a DateTime into a Date.

Because Date does not hold time nor time zone information, data will be lost during the conversion.

Examples

iex> dt = %DateTime{year: 2000, month: 2, day: 29, zone_abbr: "CET",
...>                hour: 23, minute: 0, second: 7, microsecond: {0, 0},
...>                utc_offset: 3600, std_offset: 0, time_zone: "Europe/Warsaw"}
iex> DateTime.to_date(dt)
~D[2000-02-29]

@spec to_gregorian_seconds(Calendar.datetime()) :: {integer(), non_neg_integer()}

Converts a DateTime struct to a number of gregorian seconds and microseconds.

Examples

iex> dt = %DateTime{year: 0000, month: 1, day: 1, zone_abbr: "UTC",
...>                hour: 0, minute: 0, second: 1, microsecond: {0, 0},
...>                utc_offset: 0, std_offset: 0, time_zone: "Etc/UTC"}
iex> DateTime.to_gregorian_seconds(dt)
{1, 0}

iex> dt = %DateTime{year: 2020, month: 5, day: 1, zone_abbr: "UTC",
...>                hour: 0, minute: 26, second: 31, microsecond: {5000, 0},
...>                utc_offset: 0, std_offset: 0, time_zone: "Etc/UTC"}
iex> DateTime.to_gregorian_seconds(dt)
{63_755_511_991, 5000}

iex> dt = %DateTime{year: 2020, month: 5, day: 1, zone_abbr: "CET",
...>                hour: 1, minute: 26, second: 31, microsecond: {5000, 0},
...>                utc_offset: 3600, std_offset: 0, time_zone: "Europe/Warsaw"}
iex> DateTime.to_gregorian_seconds(dt)
{63_755_511_991, 5000}

@spec to_iso8601(Calendar.datetime(), :basic | :extended, nil | integer()) ::
  String.t()

Converts the given datetime to ISO 8601:2019 format.

By default, DateTime.to_iso8601/2 returns datetimes formatted in the "extended" format, for human readability. It also supports the "basic" format through passing the :basic option.

Only supports converting datetimes which are in the ISO calendar, attempting to convert datetimes from other calendars will raise. You can also optionally specify an offset for the formatted string.

WARNING: the ISO 8601 datetime format does not contain the time zone nor its abbreviation, which means information is lost when converting to such format.

Examples

iex> dt = %DateTime{year: 2000, month: 2, day: 29, zone_abbr: "CET",
...>                hour: 23, minute: 0, second: 7, microsecond: {0, 0},
...>                utc_offset: 3600, std_offset: 0, time_zone: "Europe/Warsaw"}
iex> DateTime.to_iso8601(dt)
"2000-02-29T23:00:07+01:00"

iex> dt = %DateTime{year: 2000, month: 2, day: 29, zone_abbr: "UTC",
...>                hour: 23, minute: 0, second: 7, microsecond: {0, 0},
...>                utc_offset: 0, std_offset: 0, time_zone: "Etc/UTC"}
iex> DateTime.to_iso8601(dt)
"2000-02-29T23:00:07Z"

iex> dt = %DateTime{year: 2000, month: 2, day: 29, zone_abbr: "AMT",
...>                hour: 23, minute: 0, second: 7, microsecond: {0, 0},
...>                utc_offset: -14400, std_offset: 0, time_zone: "America/Manaus"}
iex> DateTime.to_iso8601(dt, :extended)
"2000-02-29T23:00:07-04:00"

iex> dt = %DateTime{year: 2000, month: 2, day: 29, zone_abbr: "AMT",
...>                hour: 23, minute: 0, second: 7, microsecond: {0, 0},
...>                utc_offset: -14400, std_offset: 0, time_zone: "America/Manaus"}
iex> DateTime.to_iso8601(dt, :basic)
"20000229T230007-0400"

iex> dt = %DateTime{year: 2000, month: 2, day: 29, zone_abbr: "AMT",
...>                hour: 23, minute: 0, second: 7, microsecond: {0, 0},
...>                utc_offset: -14400, std_offset: 0, time_zone: "America/Manaus"}
iex> DateTime.to_iso8601(dt, :extended, 3600)
"2000-03-01T04:00:07+01:00"

iex> dt = %DateTime{year: 2000, month: 2, day: 29, zone_abbr: "AMT",
...>                hour: 23, minute: 0, second: 7, microsecond: {0, 0},
...>                utc_offset: -14400, std_offset: 0, time_zone: "America/Manaus"}
iex> DateTime.to_iso8601(dt, :extended, 0)
"2000-03-01T03:00:07+00:00"

iex> dt = %DateTime{year: 2000, month: 3, day: 01, zone_abbr: "UTC",
...>                hour: 03, minute: 0, second: 7, microsecond: {0, 0},
...>                utc_offset: 0, std_offset: 0, time_zone: "Etc/UTC"}
iex> DateTime.to_iso8601(dt, :extended, 0)
"2000-03-01T03:00:07Z"

iex> {:ok, dt, offset} = DateTime.from_iso8601("2000-03-01T03:00:07Z")
iex> "2000-03-01T03:00:07Z" = DateTime.to_iso8601(dt, :extended, offset)

@spec to_naive(Calendar.datetime()) :: NaiveDateTime.t()

Converts the given datetime into a NaiveDateTime.

Because NaiveDateTime does not hold time zone information, any time zone related data will be lost during the conversion.

Examples

iex> dt = %DateTime{year: 2000, month: 2, day: 29, zone_abbr: "CET",
...>                hour: 23, minute: 0, second: 7, microsecond: {0, 1},
...>                utc_offset: 3600, std_offset: 0, time_zone: "Europe/Warsaw"}
iex> DateTime.to_naive(dt)
~N[2000-02-29 23:00:07.0]

@spec to_string(Calendar.datetime()) :: String.t()

Converts the given datetime to a string according to its calendar.

Examples

iex> dt = %DateTime{year: 2000, month: 2, day: 29, zone_abbr: "CET",
...>                hour: 23, minute: 0, second: 7, microsecond: {0, 0},
...>                utc_offset: 3600, std_offset: 0, time_zone: "Europe/Warsaw"}
iex> DateTime.to_string(dt)
"2000-02-29 23:00:07+01:00 CET Europe/Warsaw"

iex> dt = %DateTime{year: 2000, month: 2, day: 29, zone_abbr: "UTC",
...>                hour: 23, minute: 0, second: 7, microsecond: {0, 0},
...>                utc_offset: 0, std_offset: 0, time_zone: "Etc/UTC"}
iex> DateTime.to_string(dt)
"2000-02-29 23:00:07Z"

iex> dt = %DateTime{year: 2000, month: 2, day: 29, zone_abbr: "AMT",
...>                hour: 23, minute: 0, second: 7, microsecond: {0, 0},
...>                utc_offset: -14400, std_offset: 0, time_zone: "America/Manaus"}
iex> DateTime.to_string(dt)
"2000-02-29 23:00:07-04:00 AMT America/Manaus"

iex> dt = %DateTime{year: -100, month: 12, day: 19, zone_abbr: "CET",
...>                hour: 3, minute: 20, second: 31, microsecond: {0, 0},
...>                utc_offset: 3600, std_offset: 0, time_zone: "Europe/Stockholm"}
iex> DateTime.to_string(dt)
"-0100-12-19 03:20:31+01:00 CET Europe/Stockholm"

@spec to_time(Calendar.datetime()) :: Time.t()

Converts a DateTime into Time.

Because Time does not hold date nor time zone information, data will be lost during the conversion.

Examples

iex> dt = %DateTime{year: 2000, month: 2, day: 29, zone_abbr: "CET",
...>                hour: 23, minute: 0, second: 7, microsecond: {0, 1},
...>                utc_offset: 3600, std_offset: 0, time_zone: "Europe/Warsaw"}
iex> DateTime.to_time(dt)
~T[23:00:07.0]

@spec to_unix(Calendar.datetime(), System.time_unit()) :: integer()

Converts the given datetime to Unix time.

The datetime is expected to be using the ISO calendar with a year greater than or equal to 0.

It will return the integer with the given unit, according to System.convert_time_unit/3.

Examples

iex> 1_464_096_368 |> DateTime.from_unix!() |> DateTime.to_unix()
1464096368

iex> dt = %DateTime{calendar: Calendar.ISO, day: 20, hour: 18, microsecond: {273806, 6},
...>                minute: 58, month: 11, second: 19, time_zone: "America/Montevideo",
...>                utc_offset: -10800, std_offset: 3600, year: 2014, zone_abbr: "UYST"}
iex> DateTime.to_unix(dt)
1416517099

iex> flamel = %DateTime{calendar: Calendar.ISO, day: 22, hour: 8, microsecond: {527771, 6},
...>                minute: 2, month: 3, second: 25, std_offset: 0, time_zone: "Etc/UTC",
...>                utc_offset: 0, year: 1418, zone_abbr: "UTC"}
iex> DateTime.to_unix(flamel)
-17412508655

@spec truncate(Calendar.datetime(), :microsecond | :millisecond | :second) :: t()

Returns the given datetime with the microsecond field truncated to the given precision (:microsecond, :millisecond or :second).

The given datetime is returned unchanged if it already has lower precision than the given precision.

Examples

iex> dt1 = %DateTime{year: 2017, month: 11, day: 7, zone_abbr: "CET",
...>                 hour: 11, minute: 45, second: 18, microsecond: {123456, 6},
...>                 utc_offset: 3600, std_offset: 0, time_zone: "Europe/Paris"}
iex> DateTime.truncate(dt1, :microsecond)
#DateTime<2017-11-07 11:45:18.123456+01:00 CET Europe/Paris>

iex> dt2 = %DateTime{year: 2017, month: 11, day: 7, zone_abbr: "CET",
...>                 hour: 11, minute: 45, second: 18, microsecond: {123456, 6},
...>                 utc_offset: 3600, std_offset: 0, time_zone: "Europe/Paris"}
iex> DateTime.truncate(dt2, :millisecond)
#DateTime<2017-11-07 11:45:18.123+01:00 CET Europe/Paris>

iex> dt3 = %DateTime{year: 2017, month: 11, day: 7, zone_abbr: "CET",
...>                 hour: 11, minute: 45, second: 18, microsecond: {123456, 6},
...>                 utc_offset: 3600, std_offset: 0, time_zone: "Europe/Paris"}
iex> DateTime.truncate(dt3, :second)
#DateTime<2017-11-07 11:45:18+01:00 CET Europe/Paris>

@spec utc_now(Calendar.calendar()) :: t()

Returns the current datetime in UTC.

If you want the current time in Unix seconds, use System.os_time/1 instead.

Examples

iex> datetime = DateTime.utc_now()
iex> datetime.time_zone
"Etc/UTC"