code: def get_outbound_entity(entity: BaseEntity, private_key):
      
      if getattr(entity, "outbound_doc", None):
          # If the entity already has an outbound doc, just return the entity as is
          return entity
      outbound = None
      cls = entity.__class__
      if cls in [ActivitypubAccept, ActivitypubFollow, ActivitypubProfile]:
          # Already fine
          outbound = entity
      elif cls == Accept:
          outbound = ActivitypubAccept.from_base(entity)
      elif cls == Follow:
          outbound = ActivitypubFollow.from_base(entity)
      elif cls == Profile:
          outbound = ActivitypubProfile.from_base(entity)
      if not outbound:
          raise ValueError("Don't know how to convert this base entity to ActivityPub protocol entities.")
      # TODO LDS signing
      # if isinstance(outbound, DiasporaRelayableMixin) and not outbound.signature:
      #     # Sign by author if not signed yet. We don't want to overwrite any existing signature in the case
      #     # that this is being sent by the parent author
      #     outbound.sign(private_key)
      #     # If missing, also add same signature to `parent_author_signature`. This is required at the moment
      #     # in all situations but is apparently being removed.
      #     # TODO: remove this once Diaspora removes the extra signature
      #     outbound.parent_signature = outbound.signature
      return outbound
docs: Get the correct outbound entity for this protocol.
  
      We might have to look at entity values to decide the correct outbound entity.
      If we cannot find one, we should raise as conversion cannot be guaranteed to the given protocol.
  
      Private key of author is needed to be passed for signing the outbound entity.
  
      :arg entity: An entity instance which can be of a base or protocol entity class.
      :arg private_key: Private key of sender in str format
      :returns: Protocol specific entity class instance.
      :raises ValueError: If conversion cannot be done.