Calendar.TimeZoneDatabase.time_zone_periods_from_wall_datetime

You're seeing just the callback time_zone_periods_from_wall_datetime, go back to Calendar.TimeZoneDatabase module for more information.
Link to this callback

time_zone_periods_from_wall_datetime(arg1, arg2)

View Source (since 1.8.0)

Specs

time_zone_periods_from_wall_datetime(
  Calendar.naive_datetime(),
  Calendar.time_zone()
) ::
  {:ok, time_zone_period()}
  | {:ambiguous, time_zone_period(), time_zone_period()}
  | {:gap, {time_zone_period(), time_zone_period_limit()},
     {time_zone_period(), time_zone_period_limit()}}
  | {:error, :time_zone_not_found | :utc_only_time_zone_database}

Possible time zone periods for a certain time zone and wall clock date and time.

When the provided datetime is ambiguous a tuple with :ambiguous and two possible periods. The periods in the list are sorted with the first element being the one that begins first.

When the provided datetime is in a gap - for instance during the "spring forward" when going from winter time to summer time, a tuple with :gap and two periods with limits are returned in a nested tuple. The first nested two-tuple is the period before the gap and a naive datetime with a limit for when the period ends (wall time). The second nested two-tuple is the period just after the gap and a datetime (wall time) for when the period begins just after the gap.

If there is only a single possible period for the provided datetime, then a tuple with :ok and the time_zone_period is returned.