Add facade in oemof.solph

[Bachibouzouk]

• What functionality does it implement?
  This is related to the discussion in Setting underlying structure to implement Facade #1169, after a discussion with @uvchik we decided it might be worth testing approach B. We will link the related PR in oemof.network
• Where is it located?
  A new _facade.py file in oemof/solph/
• How does the API look?
  This is tentatively described in the examples/facade/facade.py commited file

[Bachibouzouk]

At the moment the code does not work, this is why I set the PR to draft

[Bachibouzouk]

Apparently cannot set label once it is set for renaming components in subnetwork

• let labels be overwritten in oemof-solph
• workaround with custom_properties "sub_label"

[p-snft]

Labels are meant to be unique and constant identifiers at the level of oemof.network. Why do the labels have to be changed?

[Bachibouzouk]

Because we wanted to label the components within a subnetwork in a specific way, but we found a solution, we do not change the labels, instead we use a method to label the subnetwork components right upon creation

[Bachibouzouk]

@p-snft - here we label the subnetwork node using a Facade method. We think we need to have this naming convention to be able to bookkeep the nodes for postprocessing

[Bachibouzouk]

Our aim here is to manage to create a Facade class by tempering minimally with the existing code. This creation process will help the question raise and will prompt discussion about more elegant implementations.

[p-snft]

This sounds similar to the way we did it in MTRESS:

class AbstractComponent:  # pretty much the MTRESS subnetwork

    (...)

    def create_solph_node(self, label: str, node_type: Callable, **kwargs):
        """Create a solph node and add it to the solph model."""
        _full_label = tuple(self.create_label(label))

        if label in self._solph_nodes:
            raise KeyError(
                f"Solph component named {_full_label} already exists"
            )

        _node = node_type(label=_full_label, **kwargs)

    def create_label(self, label: str) -> list[str]:
        """Return a unique label based on the identifier."""
        return self.identifier + [label]

    @property
    def identifier(self) -> list[str]:
        """Return identifier."""
        identifier = []
        highest_level = self
        while highest_level is not None:
            identifier.append(highest_level.name)
            highest_level = highest_level._nesting_element

        identifier.reverse()
        return identifier

(In reality split into AbstractComponent and NamedElement.)