Add next_period_start_in_year_span/1

README.md

@@ -20,6 +20,7 @@
 * `TzExtra.utc_datetime_range/3`
 * `TzExtra.round_datetime/3`
 * `TzExtra.advances_clock?/1`
+* `TzExtra.next_period_start_in_year_span/1`
 
 ### `TzExtra.countries_time_zones/0`
 

lib/compiler.ex

@@ -252,6 +252,13 @@ defmodule TzExtra.Compiler do
               true
           end
         end
+
+        def next_period_start_in_year_span(%DateTime{} = datetime) do
+          {from, _, _, _} = Tz.PeriodsProvider.next_period(datetime)
+
+          DateTime.from_gregorian_seconds(from)
+          |> DateTime.shift_zone!(datetime.time_zone, Tz.TimeZoneDatabase)
+        end
       end,
       for %{code: country_code} <- countries do
         {:ok, time_zones_for_country} =

test/tz_extra_test.exs

@@ -70,6 +70,16 @@ defmodule TzExtraTest do
     refute TzExtra.advances_clock?("Asia/Tokyo")
   end
 
+  test "next_period_start_in_year_span/1" do
+    {:ambiguous, first_dt, second_dt} = DateTime.new(~D[2018-10-28], ~T[02:00:00], "Europe/Copenhagen", Tz.TimeZoneDatabase)
+    dt = TzExtra.next_period_start_in_year_span(DateTime.add(first_dt, -1, :day, Tz.TimeZoneDatabase))
+    assert DateTime.compare(dt, second_dt) == :eq
+
+    {:gap, dt_just_before, dt_just_after} = DateTime.new(~D[2019-03-31], ~T[02:30:00], "Europe/Copenhagen", Tz.TimeZoneDatabase)
+    dt = TzExtra.next_period_start_in_year_span(DateTime.add(dt_just_before, -1, :day, Tz.TimeZoneDatabase))
+    assert DateTime.compare(dt, dt_just_after) == :eq
+  end
+
   test "time_zone_id_exists?/1" do
     assert TzExtra.time_zone_id_exists?("Europe/Brussels")
     assert TzExtra.time_zone_id_exists?("Europe/Amsterdam")