fix: allow booking the free part of a partly booked day

src/Controller/BookingController.php

@@ -9,6 +9,7 @@ use App\Booking\BoardPresenter;
 use App\Booking\BookingManager;
 use App\Booking\DateParam;
 use App\Booking\ResourceAlreadyBookedException;
+use App\Booking\Spot;
 use App\Booking\SeriesResult;
 use App\Booking\TimeRange;
 use App\Entity\Booking;
@@ -70,9 +71,17 @@ final class BookingController extends AbstractController
         $selected = DateParam::parseOrToday($date);
         $boardTime = BoardController::timeOf($request);
 
-        // Prefilled from whatever span the board is showing, so narrowing the board and then
-        // clicking a desk books exactly what was on screen.
-        $data = new BookingRequest($selected, $boardTime);
+        // Prefilled with the longest window still free inside the board's span -- NOT the span
+        // itself. On an all-day board a resource booked 09:00-13:00 would otherwise be offered
+        // as 00:00-24:00, collide with itself on submit, and leave the user exactly as stuck as
+        // before. Falls back to the board's span when nothing is booked at all.
+        $spot = Spot::for(
+            $resource,
+            $this->repository->findOverlapping($resource, $selected, $boardTime),
+            $boardTime,
+            $this->currentUser(),
+        );
+        $data = new BookingRequest($selected, $spot->suggested() ?? $boardTime);
 
         $form = $this->createForm(BookingType::class, $data, [
             'action' => $this->generateUrl('app_booking_new', ['id' => $resource->getId(), 'date' => $date] + $this->timeParameters($boardTime)),