fix: Daylight saving

lib/cocktail/util.ex

@@ -19,10 +19,22 @@ defmodule Cocktail.Util do
   def shift_time(datetime, opts) do
     datetime
     |> Timex.shift(opts)
+    |> shift_dst(datetime)
     |> no_ms()
   end
 
   def no_ms(time) do
     Map.put(time, :microsecond, {0, 0})
   end
+
+  # In case of datetime we may expect the same timezone hour
+  # For example after daylight saving 10h MUST still 10h the next day.
+  # This behaviour could only happen on datetime with timezone (that include `std_offset`)
+  defp shift_dst(time, datetime) do
+    if offset = Map.get(datetime, :std_offset) do
+      Timex.shift(time, seconds: offset - time.std_offset)
+    else
+      time
+    end
+  end
 end

lib/cocktail/validation/shift.ex

@@ -20,7 +20,6 @@ defmodule Cocktail.Validation.Shift do
       time
       |> shift_time("#{type}": amount)
       |> apply_option(option)
-      |> maybe_dst_change(time)
 
     {:change, new_time}
   end
@@ -30,27 +29,4 @@ defmodule Cocktail.Validation.Shift do
   defp apply_option(time, :beginning_of_day), do: time |> beginning_of_day()
   defp apply_option(time, :beginning_of_hour), do: %{time | minute: 0, second: 0, microsecond: {0, 0}}
   defp apply_option(time, :beginning_of_minute), do: %{time | second: 0, microsecond: {0, 0}}
-
-  defp maybe_dst_change(%DateTime{} = new_time, %DateTime{} = time) do
-    dst_diff = new_time.std_offset - time.std_offset
-
-    case dst_diff do
-      0 ->
-        new_time
-
-      diff ->
-        maybe_shift_time(new_time, time, diff)
-    end
-  end
-
-  defp maybe_dst_change(new_time, _time), do: new_time
-
-  defp maybe_shift_time(new_time, time, dst_diff) do
-    shifted_time = shift_time(new_time, seconds: -dst_diff)
-
-    case DateTime.compare(shifted_time, time) do
-      :eq -> new_time
-      _ -> shifted_time
-    end
-  end
 end