agorakit/agorakit

use App\Comment;
use App\User;
use Illuminate\Notifications\Messages\MailMessage;
use Illuminate\Notifications\Notification;

class MentionedUser extends Notification
{
    public function __construct(Comment $comment, User $user)
    {
        $this->comment = $comment;
        $this->user = $user;
    }

    public function via($notifiable)
    {
        return ['mail', 'database'];
    }

    public function toMail($notifiable)
    {
        $message =  (new MailMessage())
        ->subject('['.$this->comment->discussion->group->name.'] '.trans('messages.you_have_been_mentionned_by').' '.$this->user->name)
        ->line(trans('messages.you_have_been_mentionned_by').' '.$this->user->name.' '.trans('messages.in_the_discussion').' '.$this->comment->discussion->name.' : ')
        ->line(html_entity_decode(strip_tags(filter($this->comment->body))))
        ->action(trans('messages.reply'), route('groups.discussions.show', [$this->comment->discussion->group, $this->comment->discussion]))
        ->line(trans('messages.dont_reply_to_this_email'));

        if ($this->comment->discussion->inbox()) {
            $message->from($this->comment->discussion->inbox(), $this->comment->discussion->group->name);
        }
        else {
            $message->from(config('mail.noreply'), config('mail.from.name'));
        }

        return $message;
    }
}

use Notification;

class NotifyMentionedUsers
{
    public function handle(ContentCreated $event)
    {
        if ($event->model instanceof Comment) {
            $comment = $event->model;
           
            $users = $this->findUsers($comment->body);

            foreach ($users as $user) {
                if ($user->isMemberOf($comment->discussion->group)) {
                    Notification::send($user, new \App\Notifications\MentionedUser($comment, \Auth::user()));
                    flash($user->name . ' ' . trans('messages.notified'));
                }
            }
        }
    }
    //
}

use Illuminate\Foundation\Support\Providers\EventServiceProvider as ServiceProvider;

class EventServiceProvider extends ServiceProvider
{
    protected $listen = [
        'App\Events\ContentCreated' => [
            'App\Listeners\NotifyMentionedUsers',
        ],
    ];
    //
}