laravel-learn-bbs/app/Observers/ReplyObserver.php

<?php

namespace App\Observers;

use App\Models\Reply;
use App\Notifications\TopicReplied;

// creating, created, updating, updated, saving,
// saved,  deleting, deleted, restoring, restored

class ReplyObserver
{
    public function creating(Reply $reply)
    {
        $reply->setAttribute('content', clean($reply->getAttribute('content'), 'user_topic_body'));
    }

    public function updating(Reply $reply)
    {
        //
    }

    public function created(Reply $reply)
    {
        $topic = $reply->topic;
        $reply->topic->increment('reply_count', 1);
        if (!$reply->user->isAuthorOf($topic)) {
            $topic->user->notify(new TopicReplied($reply));
        }
    }
}