@spec canonical_zone?(Calendar.time_zone()) :: boolean()

Takes the name of a zone. Returns true if zone exists and is canonical. Otherwise false.

iex> Tzdata.canonical_zone? "Europe/London"
true
iex> Tzdata.canonical_zone? "Europe/Jersey"
false

@spec canonical_zone_list() :: [Calendar.time_zone()]

Like zone_list, but excludes aliases for zones.

@spec leap_second_data_valid_until() :: :calendar.datetime()

The time when the leap second information returned from the other leap second related function expires. The date-time is in UTC.

Example

Tzdata.leap_second_data_valid_until
{{2015, 12, 28}, {0, 0, 0}}

@spec leap_seconds() :: [:calendar.datetime()]

Get a list of known leap seconds. The leap seconds are datetime tuples representing the extra leap second to be inserted. The date-times are in UTC.

See also leap_seconds_with_tai_diff/1

Example

iex> Tzdata.leap_seconds() |> Enum.take(2)
[{{1972,  6, 30}, {23, 59, 60}},
 {{1972, 12, 31}, {23, 59, 60}}]

@spec leap_seconds_with_tai_diff() :: [
  %{date_time: :calendar.datetime(), tai_diff: integer()}
]

Get a list of maps with known leap seconds and the difference between UTC and the TAI in seconds.

See also leap_seconds/1

Example

iex> Tzdata.leap_seconds_with_tai_diff() |> Enum.take(2)
[%{date_time: {{1972,  6, 30}, {23, 59, 60}}, tai_diff: 11},
 %{date_time: {{1972, 12, 31}, {23, 59, 60}}, tai_diff: 12}]

@spec links() :: %{required(Calendar.time_zone()) => Calendar.time_zone()}

Returns a map of links. Also known as aliases.

iex> Tzdata.links()["Europe/Jersey"]
"Europe/London"

@spec periods(Calendar.time_zone()) :: {:ok, [time_zone_period()]} | {:error, atom()}

Returns a list of periods for the zone_name provided as an argument.

A period in this case is a period of time where the UTC offset and standard offset are in a certain way. When they change, for instance in spring when DST takes effect, a new period starts. For instance a period can begin in spring when winter time ends and summer time begins. The period lasts until DST ends.

If either the UTC or standard offset change for any reason, a new period begins. For instance instead of DST ending or beginning, a rule change that changes the UTC offset will also mean a new period.

The result is tagged with :ok if the zone_name is correct.

The from and until times can be :mix, :max or gregorian seconds.

Example

iex> Tzdata.periods("Europe/Madrid") |> elem(1) |> Enum.take(1)
[%{from: %{standard: :min, utc: :min, wall: :min}, std_off: 0,
  until: %{standard: 59989763760, utc: 59989764644, wall: 59989763760},
  utc_off: -884, zone_abbr: "LMT"}]
iex> Tzdata.periods("Not existing")
{:error, :not_found}

@spec periods_for_time(
  Calendar.time_zone(),
  gregorian_seconds(),
  :standard | :wall | :utc
) ::
  [time_zone_period()] | {:error, term()}

Get the periods that cover a certain point in time. Usually it will be a list with just one period. But in some cases it will be zero or two periods. For instance when going from summer to winter time (DST to standard time) there will be an overlap if time_type is :wall.

zone_name should be a valid time zone name. The function zone_list/0 provides a valid list of valid zone names.

time_point is the point in time in gregorian seconds (see erlang calendar module documentation for more info on gregorian seconds).

Valid values for time_type is :utc, :wall or :standard.

Examples

# 63555753600 seconds is equivalent to {{2015, 1, 1}, {0, 0, 0}}
iex> Tzdata.periods_for_time("Asia/Tokyo", 63587289600, :wall)
[%{from: %{standard: 61589289600, utc: 61589257200, wall: 61589289600}, std_off: 0,
  until: %{standard: :max, utc: :max, wall: :max}, utc_off: 32400, zone_abbr: "JST"}]

# 63612960000 seconds is equivalent to 2015-10-25 02:40:00 and is an ambiguous
# wall time for the zone. So two possible periods will be returned.
iex> Tzdata.periods_for_time("Europe/Copenhagen", 63612960000, :wall)
[%{from: %{standard: 63594813600, utc: 63594810000, wall: 63594817200}, std_off: 3600,
        until: %{standard: 63612957600, utc: 63612954000, wall: 63612961200}, utc_off: 3600, zone_abbr: "CEST"},
      %{from: %{standard: 63612957600, utc: 63612954000, wall: 63612957600}, std_off: 0,
        until: %{standard: 63626263200, utc: 63626259600, wall: 63626263200}, utc_off: 3600, zone_abbr: "CET"}]

# 63594816000 seconds is equivalent to 2015-03-29 02:40:00 and is a
# non-existing wall time for the zone. It is spring and the clock skips that hour.
iex> Tzdata.periods_for_time("Europe/Copenhagen", 63594816000, :wall)
[]

@spec tzdata_version() :: String.t()

Returns tzdata release version as a string.

Example:

Tzdata.tzdata_version
"2014i"

@spec zone_alias?(Calendar.time_zone()) :: boolean()

Takes the name of a zone. Returns true if zone exists and is an alias. Otherwise false.

iex> Tzdata.zone_alias? "Europe/Jersey"
true
iex> Tzdata.zone_alias? "Europe/London"
false

@spec zone_alias_list() :: [Calendar.time_zone()]

A list of aliases for zone names. For instance Europe/Jersey is an alias for Europe/London. Aliases are also known as linked zones.

@spec zone_exists?(String.t()) :: boolean()

Takes the name of a zone. Returns true if zone exists. Otherwise false.

iex> Tzdata.zone_exists? "Pacific/Auckland"
true
iex> Tzdata.zone_exists? "America/Sao_Paulo"
true
iex> Tzdata.zone_exists? "Europe/Jersey"
true

@spec zone_list() :: [Calendar.time_zone()]

zone_list provides a list of all the zone names that can be used with DateTime. This includes aliases.

@spec zone_lists_grouped() :: %{required(atom()) => [Calendar.time_zone()]}

Returns a map with keys being group names and the values lists of time zone names. The group names mirror the file names used by the tzinfo database.