bp_activity_edit_update_document( $document_ids )

function bp_activity_edit_update_document( $document_ids ) {
	global $bp_activity_edit, $bp_activity_post_update_id;

	if ( ( true === $bp_activity_edit || isset( $_POST['edit'] ) ) && ! empty( $bp_activity_post_update_id ) ) {
		$old_document_ids = bp_activity_get_meta( $bp_activity_post_update_id, 'bp_document_ids', true );
		$old_document_ids = explode( ',', $old_document_ids );

		if ( ! empty( $old_document_ids ) ) {

			// old document count 1 and new document uploaded count is greater than 1.
			if ( 1 === count( $old_document_ids ) && 1 < count( $document_ids ) ) {
				$old_document_id = $old_document_ids[0];

				// check if old document id is in new document uploaded.
				if ( in_array( $old_document_id, $document_ids ) ) {

					// Create new document activity for old document because it has only parent activity to show right now.
					$old_document = new BP_Document( $old_document_id );
					$args         = array(
						'hide_sitewide' => true,
						'privacy'       => 'document'
					);

					if ( ! empty( $old_document->group_id ) && bp_is_active( 'groups' ) ) {
						$args['item_id'] = $old_document->group_id;
						$args['type']    = 'activity_update';
						$current_group   = groups_get_group( $old_document->group_id );
						$args['action']  = sprintf( __( '%1$s posted an update in the group %2$s', 'buddyboss' ), bp_core_get_userlink( $old_document->user_id ), '<a href="' . bp_get_group_permalink( $current_group ) . '">' . esc_attr( $current_group->name ) . '</a>' );
						$activity_id     = groups_record_activity( $args );
					} else {
						$activity_id = bp_activity_post_update( $args );
					}

					// document activity for old document is created and it is being assigned to the old document.
					// And document activity is being saved with needed data to figure out everything for it.
					if ( $activity_id ) {
						$old_document->activity_id = $activity_id;
						$old_document->save();

						$document_activity                    = new BP_Activity_Activity( $activity_id );
						$document_activity->secondary_item_id = $bp_activity_post_update_id;
						$document_activity->save();

						// update activity meta to tell it is document activity.
						bp_activity_update_meta( $activity_id, 'bp_document_activity', '1' );

						// save attachment meta for activity.
						update_post_meta( $old_document->attachment_id, 'bp_document_activity_id', $activity_id );

						//save parent activity id in attachment meta.
						update_post_meta( $old_document->attachment_id, 'bp_document_parent_activity_id', $bp_activity_post_update_id );
					}
				}

				// old document count is greater than 1 and new document uploaded count is only 1 now.
			} else if ( 1 < count( $old_document_ids ) && 1 === count( $document_ids ) ) {
				$new_document_id = $document_ids[0];

				// check if new document is in old document uploaded, if yes then delete that document's document activity first.
				if ( in_array( $new_document_id, $old_document_ids ) ) {
					$new_document         = new BP_Document( $new_document_id );
					$document_activity_id = $new_document->activity_id;

					// delete document's assigned document activity.
					remove_action( 'bp_activity_after_delete', 'bp_document_delete_activity_document' );
					bp_activity_delete( array( 'id' => $document_activity_id ) );
					add_action( 'bp_activity_after_delete', 'bp_document_delete_activity_document' );

					//save parent activity id in document.
					$new_document->activity_id = $bp_activity_post_update_id;
					$new_document->save();

					//save parent activity id in attachment meta.
					update_post_meta( $new_document->attachment_id, 'bp_document_parent_activity_id', $bp_activity_post_update_id );
				}
			}
		}
	}

	return $document_ids;
}