How can I rename an asset file on upload when an entry is saved (Craft 3)?

Question

I have an entry type that includes an Assets field. When this entry is created/saved via the CP or a front-end form, I want to rename the Asset file as follows:

• Entry's author id. E.g: 148
• 01, 02, 03 based on how many entries the author has already submitted.

So files would look like: 148-01.jpg 148-02.jpg, 148-03.jpg.

At some point, I would also like to add the value of a custom field.

Also, I would like to limit this to entry for a certain type in a certain section: Section name: "Competitions", Entry type: "Submission".

Screenshot: https://cl.ly/a526f40c6d58

So far In my Craft 3 Module I have this. I can get the Asset id, but I can't get the Entry's Author Id:

Event::on(
    Elements::class,
    Elements::EVENT_AFTER_SAVE_ELEMENT,
    function (ElementEvent $event) {
        $asset = $event->element;
        $id = $event->element->getId();
        if ($event->isNew && $asset instanceof craft\elements\Asset) {
            $newFileName = "new-file-name-" . $id . ".jpg";
            Craft::$app->assets->moveAsset($asset, $asset->getFolder(), $newFileName);
        }
    }
);

I found this answer https://craftcms.stackexchange.com/a/13199/298, but it's for Craft 2:

craft()->on('entries.beforeSaveEntry', function(Event $event)
{
    $entry = $event->params['entry'];

    if (($entry->section['handle'] == 'friends') && ($entry->type['handle'] == 'friends'))
    {
        $title = $entry->slug;
        $assets = $entry->imgdir;

        if (count($assets) != 1)
        {
            $event->params['entry']->addError('imgdir', Craft::t('Exactly 1 asset has to be selected.'));
            $event->performAction = false;
        }
        else
        {
            $filename = $title.'.'.$assets[0]->getExtension();

            craft()->assets->renameFile($assets[0], $filename);
            craft()->assets->storeFile($assets[0]);
        }
    }
});

How can I do this in Craft 3?

Answer 1

The code below is working for me so far. The answer at https://craftcms.stackexchange.com/a/28168/298 helped me figure things out for Craft 3.

Event::on(
    Entry::class,
    Entry::EVENT_AFTER_SAVE,
    function(ModelEvent $event) {
        /** @var Entry $entry */
        $entry = $event->sender;
        //Set entry's author ID
        $authorId = $entry->authorId;
        //Set value of custom field
        $imageOrder = $entry->myCustomField;

        if ($entry->enabled && $entry->section->handle === 'mySectionHandle' && $entry->type->handle === 'myEntryTypeHandle') {
            /** @var Asset $asset */
            foreach ($entry->myAssetField as $asset) {
                $newFileName = "0" . $imageOrder . "-" . $authorId . "-" . date('YmdHis') . "." . $asset->getExtension();
                Craft::$app->assets->moveAsset($asset, $asset->getFolder(), $newFileName);
            }
        }
    }
);

Can it be improved? For e.g., can I do without the foreach loop? Let me know and I'll update this answer and then mark it as accepted.