HelperService.php

<?php

namespace App\Services;

use App\Contracts\Helper;
use Illuminate\Contracts\Container\BindingResolutionException;
use Laravel\Nova\Nova;

class HelperService implements Helper
{
    public function guessNovaRelationPosition(string $orderField): int
    {
        $lastPosition = 0;

        try {
            $request = app('request');

            if ($request->filled(['viaResource', 'viaResourceId', 'viaRelationship'])) {
                $resource = Nova::resourceForKey(
                    $request->input('viaResource')
                );

                $relationship = $request->input('viaRelationship');

                $model = $resource::$model::with($relationship)
                    ->find($request->input('viaResourceId'));

                $lastPositionalModel = $model->{$relationship}
                    ->sortByDesc($orderField)
                    ->first();

                $lastPosition = optional($lastPositionalModel)->{$orderField} ?? 0;
            }
        } catch (BindingResolutionException $exception) {
        }

        return $lastPosition + 1;
    }
}