from django.dispatch import Signal from .collection import CollectionElement from .dispatch import SignalConnectMetaClass class ProjectorElement(object, metaclass=SignalConnectMetaClass): """ Base class for an element on the projector. Every app which wants to add projector elements has to create classes subclassing from this base class with different names. The name attribute has to be set. The metaclass (SignalConnectMetaClass) does the rest of the magic. """ signal = Signal() name = None def __init__(self, **kwargs): """ Initializes the projector element instance. This is done when the signal is sent. Because of Django's signal API, we have to take wildcard keyword arguments. But they are not used here. """ pass @classmethod def get_dispatch_uid(cls): """ Returns the classname as a unique string for each class. Returns None for the base class so it will not be connected to the signal. """ if not cls.__name__ == 'ProjectorElement': return cls.__name__ def check_and_update_data(self, projector_object, config_entry): """ Checks projector element data via self.check_data() and updates them via self.update_data(). The projector object and the config entry have to be given. """ self.projector_object = projector_object self.config_entry = config_entry assert self.config_entry.get('name') == self.name, ( 'To get data of a projector element, the correct config entry has to be given.') self.check_data() return self.update_data() or {} def check_data(self): """ Method can be overridden to validate projector element data. This may raise ProjectorException in case of an error. Default: Does nothing. """ pass def update_data(self): """ Method can be overridden to update the projector element data output. This should return a dictonary. Use this for server calculated data which have to be forwared to the client. Default: Does nothing. """ pass def get_requirements(self, config_entry): """ Returns an iterable of instances that are required for this projector element. The config_entry has to be given. """ return () def get_requirements_as_collection_elements(self, config_entry): """ Returns an iterable of collection elements that are required for this projector element. The config_entry has to be given. """ return (CollectionElement.from_instance(instance) for instance in self.get_requirements(config_entry)) def get_collection_elements_required_for_this(self, collection_element, config_entry): """ Returns a list of CollectionElements that have to be sent to every projector that shows this projector element according to the given collection_element. Default: Returns only the collection_element if it belongs to the requirements but return all requirements if the projector changes. """ requirements_as_collection_elements = list(self.get_requirements_as_collection_elements(config_entry)) for requirement in requirements_as_collection_elements: if collection_element == requirement: output = [collection_element] break else: if collection_element.information.get('this_projector'): output = [collection_element] output.extend(requirements_as_collection_elements) else: output = [] return output