how to get weight or delta of current field collection item that is being computed
I was searching in wrong path :( this is found at 

http://drupalcontrib.org/api/drupal/contributions!field_collection!field_collection.module/class/FieldCollectionItemEntity/7

code for getting delta is

$wrapper = entity_metadata_wrapper('field_collection_item', $entity);
$cur_delta=$wrapper-&gt;delta();