Which Hook can I use when creating unique post but not update/save/delete

Question

I want to have a numerical counter for a CPT in a custom field a bit like a post ID but only for that custom post type, starting from 1. I've tried to start by setting a custom field value from an incrementing value in options when a post is first created.

I'm trying to call this and increment on new post save but it keeps over-writing it when post is saved/updated, etc so I'm using the wrong hook but can't seem to find the right one.

// Maintain Asset register count in Options Table and assign to new assets
function define_asset( $post_id, $post ) {
    if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) return;
    if ( ! current_user_can( 'edit_post', $post_id ) ) return;
    global $wpdb;
    $isAsset = get_post_meta($post_id, 'assetID', false);
    if ($isAsset ) {
        if(get_option('assetID')){
        $count = get_option('assetID', true);
        update_option('assetID', $count+1);
        $assetID = get_option('assetId');
        str_pad($assetID, 5, '0', STR_PAD_LEFT);
        } else {
        /** This will automatically add the option if it does not exist. **/
        update_option('assetID', 1); // adding first time as value 1
        }
        $assetID = str_pad($assetID, 5, '0', STR_PAD_LEFT);
        update_post_meta( $post_id, 'assetID', $assetID );
    }
}
//add_action( 'post_updated',  'define_asset', 20, 2 ); 
add_action( 'save_post', 'define_asset', 20, 2 ); // This works but increments on each save
//add_action( 'publish_post', 'define_asset', 20, 2 ); // This works but increments on each save
//add_action( 'publish_inventory',  'define_asset', 20, 2 ); // 
//add_action( 'draft_to_published',  'define_asset', 20, 2 ); // This doesn't work

Answer 1

The save_post hook has a third parameter named $update, so you can use it to check if the post is being created and not updated.

function define_asset( $post_id, $post, $update ) {
    if ( $update ) {
        return;
    }

    // else, run your code...
}
add_action( 'save_post', 'define_asset', 20, 3 );