mandant-crm/backend/app/Modules/History/Requests/UpdateHistoryEntryRequest.php

<?php

namespace App\Modules\History\Requests;

use App\Modules\History\Models\HistoryEntry;
use Illuminate\Contracts\Validation\Validator;
use Illuminate\Foundation\Http\FormRequest;

class UpdateHistoryEntryRequest extends FormRequest
{
    public function authorize(): bool { return true; }

    public function rules(): array
    {
        return [
            'body' => ['required', 'string', 'max:65535'],
            'occurred_at' => ['nullable', 'date_format:Y-m-d\TH:i:s'],
        ];
    }

    public function withValidator(Validator $validator): void
    {
        $validator->after(function (Validator $validator) {
            $entry = $this->route('historyEntry');

            if ($entry instanceof HistoryEntry
                && $entry->entryType?->requires_datetime
                && ! $this->filled('occurred_at')
            ) {
                $validator->errors()->add(
                    'occurred_at',
                    'Für diesen Verlaufstyp sind Datum und Uhrzeit erforderlich.'
                );
            }
        });
    }
}