Merge branch 'peek-travel:main' into main

lib/cocktail/validation/shift.ex

@@ -20,6 +20,7 @@ defmodule Cocktail.Validation.Shift do
       time
       |> shift_time("#{type}": amount)
       |> apply_option(option)
+      |> maybe_dst_change(time)
 
     {:change, new_time}
   end
@@ -29,4 +30,27 @@ 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