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#
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import typing


# # 🥭 TWatched generic type
#
# Just a generic type name for watchers.
#
TWatched = typing.TypeVar("TWatched", covariant=True)


# # 🥭 Watcher protocol
#
# The `Watcher` protocol just says the object has a property `latest` of type `TWatched`.
#
# The idea behind this is that we can have an object that's subscribed to a websocket and updates, say,
# the Group. But instead of having to explicitly reference websocket implementation details or force
# a common base class on all watchers, we can use the protocol to have any object be a `Watcher` as long
# as it provides a `latest` property of the appropriate type.
#
class Watcher(typing.Protocol[TWatched]):
    @property
    def latest(self) -> TWatched:
        raise NotImplementedError("Watcher.latest is not implemented on the Protocol.")


# # 🥭 ManualUpdateWatcher class
#
# The `ManualUpdateWatcher` class provides a basic implementation of the `Watcher` protocol that
# requires manual intervention (updating of the `value` member) to set the latest version.
#
class ManualUpdateWatcher(typing.Generic[TWatched]):
    def __init__(self, value: TWatched) -> None:
        self.value: TWatched = value

    @property
    def latest(self) -> TWatched:
        return self.value


# # 🥭 LamdaUpdateWatcher class
#
# The `LamdaUpdateWatcher` class provides a basic implementation of the `Watcher` protocol that
# calls a lambda to determine the latest version.
#
class LamdaUpdateWatcher(typing.Generic[TWatched]):
    def __init__(self, accessor: typing.Callable[[], TWatched]) -> None:
        self.accessor: typing.Callable[[], TWatched] = accessor

    @property
    def latest(self) -> TWatched:
        return self.accessor()