Replace delimiter_to_number/1 hack with sort_periods/1

lib/tzdata.ex

@@ -241,7 +241,8 @@ defmodule Tzdata do
   defp possible_periods_for_zone_and_time(zone_name, time_point, time_type) do
     {:ok, periods} = Tzdata.ReleaseReader.periods_for_zone_time_and_type(zone_name, time_point, time_type)
     mapped_periods = periods
-    |> Enum.sort_by(fn {_, from_utc, _, _, _, _, _, _, _, _} -> -(from_utc |> Tzdata.ReleaseReader.delimiter_to_number) end)
+    |> Tzdata.ReleaseReader.sort_periods()
+    |> Enum.reverse
     |> Enum.map(
       fn {_, f_utc, f_wall, f_std, u_utc, u_wall, u_std, utc_off, std_off, zone_abbr} ->
             %{

lib/tzdata/release_reader.ex

@@ -43,8 +43,7 @@ defmodule Tzdata.ReleaseReader do
   defp do_periods_for_zone(zone) do
     case lookup_periods_for_zone(zone) do
       periods when is_list(periods) ->
-        periods
-        |> Enum.sort_by(fn period -> elem(period, 1) |> delimiter_to_number() end)
+        sort_periods(periods)
 
       _ ->
         nil
@@ -57,18 +56,31 @@ defmodule Tzdata.ReleaseReader do
   defp lookup_periods_for_zone(_), do: []
 
   @doc !"""
-       Hack which is useful for sorting periods. Delimiters can be integers representing
-       gregorian seconds or :min or :max. By converting :min and :max to integers, they are
-       easier to sort. It is assumed that the fake numbers they are converted to are far beyond
-       numbers used.
        TODO: Instead of doing this, do the sorting before inserting. When reading from a bag the order
        should be preserved.
        """
-  @very_high_number_representing_gregorian_seconds 9_315_537_984_000
-  @low_number_representing_before_year_0 -1
-  def delimiter_to_number(:min), do: @low_number_representing_before_year_0
-  def delimiter_to_number(:max), do: @very_high_number_representing_gregorian_seconds
-  def delimiter_to_number(integer) when is_integer(integer), do: integer
+  def sort_periods(periods), do: Enum.sort(periods, &periods_ordered?/2)
+
+  defp periods_ordered?(
+         {_, _, _, _, _, _, _, _, _, _},
+         {_, :min, _, _, _, _, _, _, _, _}
+       ),
+       do: false
+
+  defp periods_ordered?(
+         {_, :max, _, _, _, _, _, _, _, _},
+         {_, _, _, _, _, _, _, _, _, _}
+       ),
+       do: false
+
+  defp periods_ordered?(
+         {_, left, _, _, _, _, _, _, _, _},
+         {_, right, _, _, _, _, _, _, _, _}
+       )
+       when is_integer(left) and is_integer(right) and left > right,
+       do: false
+
+  defp periods_ordered?(_, _), do: true
 
   defp current_release_from_table do
     :ets.lookup(:tzdata_current_release, :release_version) |> hd |> elem(1)