class TaskCreatorMetaclass(type):
    # create_doit_tasks is expected to take no arguments when doit calls it.
    # Still, we want to be able to access self while tasks are being created. 
    # 
    # If an instance of a class with a create_doit_tasks function is called
    # via dot notation, _as is presently done in doit_, Python's descriptor
    # protocol applies; the instance's call of create_doit_task will be
    # converted into a bound method with implicit self (i.e. the normal case
    # with dot notation calling an instance method, where the self parameter
    # becomes a hidden first argument).
    #
    # Doit looks for _any_ objects in scope with a create_doit_tasks method
    # when loading tasks from a module; _this includes classes, which are also
    # object/instances (with a type of some sort of metaclass)!_. However, for
    # the class definitions, the descriptor protocol doesn't kick in. This is
    # because descriptors only kick in for class attributes, and From the POV
    # of the class definitions, create_doit_task is an attribute on the class
    # object _instance_, not a class attribute. So when doit tries to call
    # create_doit_task on a class object, create_doit_tasks is expecting a self
    # argument that wasn't provided. 
    #
    # Tweak class creation so that the create_doit_tasks attribute is hidden
    # from doit and thus doit skips looking for tasks from the class objects.
    def __getattribute__(self, name: str):
        if name in ("create_doit_tasks",):
            raise AttributeError
        else:
            return super().__getattribute__(name)


class ZfsList(metaclass=TaskCreatorMetaclass):
    def __init__(self, config):
        self.config = config
        super().__init__()

    def build_cmd(self, pool, book):
        return f"zfs list -H -rtsnap{',bookmark' if book else ''} -o name {pool}"

    def create_doit_tasks(self):
        # We run zfs list several times- sometimes the same command!- to reduce the
        # probability of TOCTOU problems.
        yield {
            "name": "pre_create",
            "actions": [CmdAction(self.build_cmd(self.config.from_, True), save_out="snapbooks_raw")],
            "verbosity": 0,
        }

        yield {
            "name": "pre_prepare",
            "actions": [CmdAction(self.build_cmd(self.config.to, False), save_out="snaps_raw")],
            "verbosity": 0,
        }

        yield {
            "name": "pre_send_from",
            "actions": [CmdAction(self.build_cmd(self.config.from_, True), save_out="from_raw")],
            "verbosity": 0,
        }

        yield {
            "name": "pre_send_to",
            "actions": [CmdAction(self.build_cmd(self.config.to, False), save_out="to_raw")],
            "verbosity": 0,
        }