agorakit/agorakit

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

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

use App\Comment;
use App\Discussion;
use App\Group;
use Auth;
use Illuminate\Http\Request;

/**
 * Comments CRUD controller.
 */
class CommentController extends Controller
{
    public function store(Request $request, Group $group, Discussion $discussion)
    {
        $comment = new \App\Comment();
        $comment->body = $request->input('body');
        $comment->user()->associate(\Auth::user());

        event(new \App\Events\ContentCreated($comment));
    }
}

use App\Events\ContentCreated;
use Notification;

class NotifyMentionedUsers
{
    public function handle(ContentCreated $event)
    {
        $user = $comment->discussion->group->users->where('username', $username)->first();
        if ($user) {
            Notification::send($user, new \App\Notifications\MentionedUser($comment, \Auth::user()));
            flash($user->name.' '.trans('messages.notified'));
        }
    }
}