public function store(CreateTripRequest $request, FlashNotifier $flash)
 {
     if (!Shuttle::find($request->shuttle_id)) {
         $flash->error("Error creating trip. Shuttle {$request->id} does not exist.");
         return redirect()->back()->withInput();
     }
     $driver = User::find($request->driver_id);
     if ($driver == null) {
         $flash->error("Error creating trip. User {$request->driver_id} does not exist.");
         return redirect()->back()->withInput();
     }
     if (!$driver->isDriver()) {
         $flash->error("Error creating trip. User {$driver->name} is not a driver.");
         return redirect()->back()->withInput();
     }
     $leaves = new Carbon($request->leaves_at);
     $arrives = new Carbon($request->arrives_at);
     Trip::create(['shuttle_id' => $request->shuttle_id, 'driver_id' => $request->driver_id, 'origin' => $request->origin, 'destination' => $request->destination, 'leaves_at' => $leaves, 'arrives_at' => $arrives]);
     $flash->success('Trip successfully created!');
     return back();
 }