import inspect
import pickle
import marshal
import types
import sqlite3
import collections
import collections.abc
import keyword
import weakref


class Handle:
    """Handle defines a name for an object in the form of a hierarchical path.

    The provided parent is the object (or that object's handle) that this handle
    sits under, or None if the object identified by this handle stands by itself
    as the root of its own hierarchy.

    The handle kind is a string that defines a namespace so objects with the
    same parent and kind will have unique keys.

    The handle key is a string uniquely identifying the object. No other objects
    under the same parent and kind may have the same key.
    """

    def __init__(self, parent, kind, key):
        if parent and not isinstance(parent, Handle):
            parent = parent.handle
        self._parent = parent
        self._kind = kind
        self._key = key
        if parent:
            if key:
                self._path = f"{parent}/{kind}[{key}]"
            else:
                self._path = f"{parent}/{kind}"
        else:
            if key:
                self._path = f"{kind}[{key}]"
            else:
                self._path = f"{kind}"

    def nest(self, kind, key):
        return Handle(self, kind, key)

    def __hash__(self):
        return hash((self.parent, self.kind, self.key))

    def __eq__(self, other):
        return (self.parent, self.kind, self.key) == (other.parent, other.kind, other.key)

    def __str__(self):
        return self.path

    @property
    def parent(self):
        return self._parent

    @property
    def kind(self):
        return self._kind

    @property
    def key(self):
        return self._key

    @property
    def path(self):
        return self._path

    @classmethod
    def from_path(cls, path):
        handle = None
        for pair in path.split("/"):
            pair = pair.split("[")
            good = False
            if len(pair) == 1:
                kind, key = pair[0], None
                good = True
            elif len(pair) == 2:
                kind, key = pair
                if key and key[-1] == ']':
                    key = key[:-1]
                    good = True
            if not good:
                raise RuntimeError("attempted to restore invalid handle path {path}")
            handle = Handle(handle, kind, key)
        return handle


class EventBase:

    def __init__(self, handle):
        self.handle = handle
        self.deferred = False

    def defer(self):
        self.deferred = True

    def snapshot(self):
        """Return the snapshot data that should be persisted.

        Subclasses must override to save any custom state.
        """
        return None

    def restore(self, snapshot):
        """Restore the value state from the given snapshot.

        Subclasses must override to restore their custom state.
        """
        self.deferred = False


class EventSource:
    """EventSource wraps an event type with a descriptor to facilitate observing and emitting.

    It is generally used as:

        class SomethingHappened(EventBase):
            pass

        class SomeObject(Object):
            something_happened = EventSource(SomethingHappened)

    With that, instances of that type will offer the someobj.something_happened
    attribute which is a BoundEvent and may be used to emit and observe the event.
    """

    def __init__(self, event_type):
        if not isinstance(event_type, type) or not issubclass(event_type, EventBase):
            raise RuntimeError(f"Event requires a subclass of EventBase as an argument, got {event_type}")
        self.event_type = event_type
        self.event_kind = None
        self.emitter_type = None

    def __set_name__(self, emitter_type, event_kind):
        if self.event_kind is not None:
            raise RuntimeError(
                f'EventSource({self.event_type.__name__}) reused as '
                f'{self.emitter_type.__name__}.{self.event_kind} and '
                f'{emitter_type.__name__}.{event_kind}')
        self.event_kind = event_kind
        self.emitter_type = emitter_type

    def __get__(self, emitter, emitter_type=None):
        if emitter is None:
            return self
        # Framework might not be available if accessed as CharmClass.on.event rather than charm_instance.on.event,
        # but in that case it couldn't be emitted anyway, so there's no point to registering it.
        framework = getattr(emitter, 'framework', None)
        if framework is not None:
            framework.register_type(self.event_type, emitter, self.event_kind)
        return BoundEvent(emitter, self.event_type, self.event_kind)


class BoundEvent:

    def __repr__(self):
        return (f'<BoundEvent {self.event_type.__name__} bound to '
                f'{type(self.emitter).__name__}.{self.event_kind} '
                f'at {hex(id(self))}>')

    def __init__(self, emitter, event_type, event_kind):
        self.emitter = emitter
        self.event_type = event_type
        self.event_kind = event_kind

    def emit(self, *args, **kwargs):
        """Emit event to all registered observers.

        The current storage state is committed before and after each observer is notified.
        """
        framework = self.emitter.framework
        key = framework._next_event_key()
        event = self.event_type(Handle(self.emitter, self.event_kind, key), *args, **kwargs)
        framework._emit(event)


class HandleKind:
    """Helper descriptor to define the Object.handle_kind field.

    The handle_kind for an object defaults to its type name, but it may
    be explicitly overridden if desired.
    """

    def __get__(self, obj, obj_type):
        kind = obj_type.__dict__.get("handle_kind")
        if kind:
            return kind
        return obj_type.__name__


class Object:

    handle_kind = HandleKind()

    def __init__(self, parent, key):
        kind = self.handle_kind
        if isinstance(parent, Framework):
            self.framework = parent
            # Avoid Framework instances having a circular reference to themselves.
            if self.framework is self:
                self.framework = weakref.proxy(self.framework)
            self.handle = Handle(None, kind, key)
        else:
            self.framework = parent.framework
            self.handle = Handle(parent, kind, key)
        self.framework._track(self)

        # TODO Detect conflicting handles here.

    @property
    def model(self):
        return self.framework.model

    @property
    def meta(self):
        return self.framework.meta

    @property
    def charm_dir(self):
        return self.framework.charm_dir


class EventsBase(Object):
    """Convenience type to allow defining .on attributes at class level."""

    handle_kind = "on"

    def __init__(self, parent=None, key=None):
        if parent is not None:
            super().__init__(parent, key)
        else:
            self._cache = weakref.WeakKeyDictionary()

    def __get__(self, emitter, emitter_type):
        if emitter is None:
            return self
        instance = self._cache.get(emitter)
        if instance is None:
            # Same type, different instance, more data. Doing this unusual construct
            # means people can subclass just this one class to have their own 'on'.
            instance = self._cache[emitter] = type(self)(emitter)
        return instance

    @classmethod
    def define_event(cls, event_kind, event_type):
        """Define an event on this type at runtime.

        cls -- a type to define an event on.
        event_kind -- an attribute name that will be used to access the event. Must be a valid python identifier, not be a keyword or an existing attribute.
        event_type -- a type of the event to define.
        """
        if not event_kind.isidentifier():
            raise RuntimeError(f'unable to define an event with event_kind that is not a valid python identifier: {event_kind}')
        elif keyword.iskeyword(event_kind):
            raise RuntimeError(f'unable to define an event with event_kind that is a python keyword: {event_kind}')
        try:
            getattr(cls, event_kind)
            raise RuntimeError(f'unable to define an event with event_kind that overlaps with an existing type {cls} attribute: {event_kind}')
        except AttributeError:
            pass

        event_descriptor = EventSource(event_type)
        event_descriptor.__set_name__(cls, event_kind)
        setattr(cls, event_kind, event_descriptor)

    def events(self):
        """Return a mapping of event_kinds to bound_events for all available events.
        """
        events_map = {}
        # We have to iterate over the class rather than instance to allow for properties which
        # might call this method (e.g., event views), leading to infinite recursion.
        for attr_name, attr_value in inspect.getmembers(type(self)):
            if isinstance(attr_value, EventSource):
                # We actually care about the bound_event, however, since it
                # provides the most info for users of this method.
                event_kind = attr_name
                bound_event = getattr(self, event_kind)
                events_map[event_kind] = bound_event
        return events_map

    def __getitem__(self, key):
        return PrefixedEvents(self, key)


class PrefixedEvents:

    def __init__(self, emitter, key):
        self._emitter = emitter
        self._prefix = key.replace("-", "_") + '_'

    def __getattr__(self, name):
        return getattr(self._emitter, self._prefix + name)


class PreCommitEvent(EventBase):
    pass


class CommitEvent(EventBase):
    pass


class FrameworkEvents(EventsBase):
    pre_commit = EventSource(PreCommitEvent)
    commit = EventSource(CommitEvent)


class NoSnapshotError(Exception):

    def __init__(self, handle_path):
        self.handle_path = handle_path

    def __str__(self):
        return f'no snapshot data found for {self.handle_path} object'


class NoTypeError(Exception):

    def __init__(self, handle_path):
        self.handle_path = handle_path

    def __str__(self):
        return f"cannot restore {self.handle_path} since no class was registered for it"


class SQLiteStorage:

    def __init__(self, filename):
        self._db = sqlite3.connect(str(filename), isolation_level="EXCLUSIVE")
        self._setup()

    def _setup(self):
        c = self._db.execute("BEGIN")
        c.execute("SELECT count(name) FROM sqlite_master WHERE type='table' AND name='snapshot'")
        if c.fetchone()[0] == 0:
            # Keep in mind what might happen if the process dies somewhere below.
            # The system must not be rendered permanently broken by that.
            self._db.execute("CREATE TABLE snapshot (handle TEXT PRIMARY KEY, data BLOB)")
            self._db.execute("CREATE TABLE notice (sequence INTEGER PRIMARY KEY AUTOINCREMENT, event_path TEXT, observer_path TEXT, method_name TEXT)")
            self._db.commit()

    def close(self):
        self._db.close()

    def commit(self):
        self._db.commit()

    # There's commit but no rollback. For abort to be supported, we'll need logic that
    # can rollback decisions made by third-party code in terms of the internal state
    # of objects that have been snapshotted, and hooks to let them know about it and
    # take the needed actions to undo their logic until the last snapshot.
    # This is doable but will increase significantly the chances for mistakes.

    def save_snapshot(self, handle_path, snapshot_data):
        self._db.execute("REPLACE INTO snapshot VALUES (?, ?)", (handle_path, snapshot_data))

    def load_snapshot(self, handle_path):
        c = self._db.cursor()
        c.execute("SELECT data FROM snapshot WHERE handle=?", (handle_path,))
        row = c.fetchone()
        if row:
            return row[0]
        return None

    def drop_snapshot(self, handle_path):
        self._db.execute("DELETE FROM snapshot WHERE handle=?", (handle_path,))

    def save_notice(self, event_path, observer_path, method_name):
        self._db.execute("INSERT INTO notice VALUES (NULL, ?, ?, ?)", (event_path, observer_path, method_name))

    def drop_notice(self, event_path, observer_path, method_name):
        self._db.execute("DELETE FROM notice WHERE event_path=? AND observer_path=? AND method_name=?", (event_path, observer_path, method_name))

    def notices(self, event_path):
        if event_path:
            c = self._db.execute("SELECT event_path, observer_path, method_name FROM notice WHERE event_path=? ORDER BY sequence", (event_path,))
        else:
            c = self._db.execute("SELECT event_path, observer_path, method_name FROM notice ORDER BY sequence")
        while True:
            rows = c.fetchmany()
            if not rows:
                break
            for row in rows:
                yield tuple(row)


class Framework(Object):

    on = FrameworkEvents()

    # Override properties from Object so that we can set them in __init__.
    model = None
    meta = None
    charm_dir = None

    def __init__(self, data_path, charm_dir, meta, model):

        super().__init__(self, None)

        self._data_path = data_path
        self.charm_dir = charm_dir
        self.meta = meta
        self.model = model
        self._observers = []      # [(observer_path, method_name, parent_path, event_key)]
        self._observer = weakref.WeakValueDictionary()       # {observer_path: observer}
        self._objects = weakref.WeakValueDictionary()
        self._type_registry = {}  # {(parent_path, kind): cls}
        self._type_known = set()  # {cls}

        self._storage = SQLiteStorage(data_path)

        # We can't use the higher-level StoredState because it relies on events.
        self.register_type(StoredStateData, None, StoredStateData.handle_kind)
        stored_handle = Handle(None, StoredStateData.handle_kind, '_stored')
        try:
            self._stored = self.load_snapshot(stored_handle)
        except NoSnapshotError:
            self._stored = StoredStateData(self, '_stored')
            self._stored['event_count'] = 0

    def close(self):
        self._storage.close()

    def _track(self, obj):
        """Track object and ensure it is the only object created using its handle path."""
        if obj is self:
            # Framework objects don't track themselves
            return
        if obj.handle.path in self.framework._objects:
            raise RuntimeError(f"two objects claiming to be {obj.handle.path} have been created")
        self._objects[obj.handle.path] = obj

    def _forget(self, obj):
        """Stop tracking the given object. See also _track."""
        self._objects.pop(obj.handle.path, None)

    def commit(self):
        # Give a chance for objects to persist data they want to before a commit is made.
        self.on.pre_commit.emit()
        # Make sure snapshots are saved by instances of StoredStateData. Any possible state
        # modifications in on_commit handlers of instances of other classes will not be persisted.
        self.on.commit.emit()
        # Save our event count after all events have been emitted.
        self.save_snapshot(self._stored)
        self._storage.commit()

    def register_type(self, cls, parent, kind=None):
        if parent and not isinstance(parent, Handle):
            parent = parent.handle
        if parent:
            parent_path = parent.path
        else:
            parent_path = None
        if not kind:
            kind = cls.handle_kind
        self._type_registry[(parent_path, kind)] = cls
        self._type_known.add(cls)

    def save_snapshot(self, value):
        """Save a persistent snapshot of the provided value.

        The provided value must implement the following interface:

        value.handle = Handle(...)
        value.snapshot() => {...}  # Simple builtin types only.
        value.restore(snapshot)    # Restore custom state from prior snapshot.
        """
        if type(value) not in self._type_known:
            raise RuntimeError(f"cannot save {type(value).__name__} values before registering that type")
        data = value.snapshot()
        # Use marshal as a validator, enforcing the use of simple types.
        marshal.dumps(data)
        # Use pickle for serialization, so the value remains portable.
        raw_data = pickle.dumps(data)
        self._storage.save_snapshot(value.handle.path, raw_data)

    def load_snapshot(self, handle):
        parent_path = None
        if handle.parent:
            parent_path = handle.parent.path
        cls = self._type_registry.get((parent_path, handle.kind))
        if not cls:
            raise NoTypeError(handle.path)
        raw_data = self._storage.load_snapshot(handle.path)
        if not raw_data:
            raise NoSnapshotError(handle.path)
        data = pickle.loads(raw_data)
        obj = cls.__new__(cls)
        obj.framework = self
        obj.handle = handle
        obj.restore(data)
        self._track(obj)
        return obj

    def drop_snapshot(self, handle):
        self._storage.drop_snapshot(handle.path)

    def observe(self, bound_event, observer):
        """Register observer to be called when bound_event is emitted.

        The bound_event is generally provided as an attribute of the object that emits
        the event, and is created in this style:

            class SomeObject:
                something_happened = Event(SomethingHappened)

        That event may be observed as:

            framework.observe(someobj.something_happened, self.on_something_happened)

        If the method to be called follows the name convention "on_<event name>", it
        may be omitted from the observe call. That means the above is equivalent to:

            framework.observe(someobj.something_happened, self)

        """
        if not isinstance(bound_event, BoundEvent):
            raise RuntimeError(f'Framework.observe requires a BoundEvent as second parameter, got {bound_event}')

        event_type = bound_event.event_type
        event_kind = bound_event.event_kind
        emitter = bound_event.emitter

        self.register_type(event_type, emitter, event_kind)

        if hasattr(emitter, "handle"):
            emitter_path = emitter.handle.path
        else:
            raise RuntimeError(f'event emitter {type(emitter).__name__} must have a "handle" attribute')

        method_name = None
        if isinstance(observer, types.MethodType):
            method_name = observer.__name__
            observer = observer.__self__
        else:
            method_name = "on_" + event_kind
            if not hasattr(observer, method_name):
                raise RuntimeError(f'Observer method not provided explicitly and {type(observer).__name__} type has no "{method_name}" method')

        # Validate that the method has an acceptable call signature.
        sig = inspect.signature(getattr(observer, method_name))
        # Self isn't included in the params list, so the first arg will be the event.
        extra_params = list(sig.parameters.values())[1:]
        if not sig.parameters:
            raise TypeError(f'{type(observer).__name__}.{method_name} must accept event parameter')
        elif any(param.default is inspect.Parameter.empty for param in extra_params):
            # Allow for additional optional params, since there's no reason to exclude them, but
            # required params will break.
            raise TypeError(f'{type(observer).__name__}.{method_name} has extra required parameter')

        # TODO Prevent the exact same parameters from being registered more than once.

        self._observer[observer.handle.path] = observer
        self._observers.append((observer.handle.path, method_name, emitter_path, event_kind))

    def _next_event_key(self):
        """Return the next event key that should be used, incrementing the internal counter."""
        # Increment the count first; this means the keys will start at 1, and 0 means no events have been emitted.
        self._stored['event_count'] += 1
        return str(self._stored['event_count'])

    def _emit(self, event):
        """See BoundEvent.emit for the public way to call this."""

        # Save the event for all known observers before the first notification
        # takes place, so that either everyone interested sees it, or nobody does.
        self.save_snapshot(event)
        event_path = event.handle.path
        event_kind = event.handle.kind
        parent_path = event.handle.parent.path
        # TODO Track observers by (parent_path, event_kind) rather than as a list of all observers. Avoiding linear search through all observers for every event
        for observer_path, method_name, _parent_path, _event_kind in self._observers:
            if _parent_path != parent_path:
                continue
            if _event_kind and _event_kind != event_kind:
                continue
            # Again, only commit this after all notices are saved.
            self._storage.save_notice(event_path, observer_path, method_name)
        self._reemit(event_path)

    def reemit(self):
        """Reemit previously deferred events to the observers that deferred them.

        Only the specific observers that have previously deferred the event will be
        notified again. Observers that asked to be notified about events after it's
        been first emitted won't be notified, as that would mean potentially observing
        events out of order.
        """
        self._reemit()

    def _reemit(self, single_event_path=None):
        last_event_path = None
        deferred = True
        for event_path, observer_path, method_name in self._storage.notices(single_event_path):
            event_handle = Handle.from_path(event_path)

            if last_event_path != event_path:
                if not deferred:
                    self._storage.drop_snapshot(last_event_path)
                last_event_path = event_path
                deferred = False

            try:
                event = self.load_snapshot(event_handle)
            except NoTypeError:
                self._storage.drop_notice(event_path, observer_path, method_name)
                continue

            event.deferred = False
            observer = self._observer.get(observer_path)
            if observer:
                custom_handler = getattr(observer, method_name, None)
                if custom_handler:
                    custom_handler(event)

            if event.deferred:
                deferred = True
            else:
                self._storage.drop_notice(event_path, observer_path, method_name)
            # We intentionally consider this event to be dead and reload it from scratch in the next path.
            self.framework._forget(event)

        if not deferred:
            self._storage.drop_snapshot(last_event_path)


class StoredStateChanged(EventBase):
    pass


class StoredStateEvents(EventsBase):
    changed = EventSource(StoredStateChanged)


class StoredStateData(Object):

    on = StoredStateEvents()

    def __init__(self, parent, attr_name):
        super().__init__(parent, attr_name)
        self._cache = {}
        self.dirty = False

    def __getitem__(self, key):
        return self._cache.get(key)

    def __setitem__(self, key, value):
        self._cache[key] = value
        self.dirty = True

    def __contains__(self, key):
        return key in self._cache

    def snapshot(self):
        return self._cache

    def restore(self, snapshot):
        self._cache = snapshot
        self.dirty = False

    def on_commit(self, event):
        if self.dirty:
            self.framework.save_snapshot(self)
            self.dirty = False


class BoundStoredState:

    def __init__(self, parent, attr_name):
        parent.framework.register_type(StoredStateData, parent)

        handle = Handle(parent, StoredStateData.handle_kind, attr_name)
        try:
            data = parent.framework.load_snapshot(handle)
        except NoSnapshotError:
            data = StoredStateData(parent, attr_name)

        # __dict__ is used to avoid infinite recursion.
        self.__dict__["_data"] = data
        self.__dict__["_attr_name"] = attr_name

        parent.framework.observe(parent.framework.on.commit, self._data)

    def __getattr__(self, key):
        # "on" is the only reserved key that can't be used in the data map.
        if key == "on":
            return self._data.on
        if key not in self._data:
            raise AttributeError(f"attribute '{key}' is not stored")
        return _wrap_stored(self._data, self._data[key])

    def __setattr__(self, key, value):
        if key == "on":
            raise AttributeError(f"attribute 'on' is reserved and cannot be set")

        value = _unwrap_stored(self._data, value)

        if not isinstance(value, (type(None), int, str, bytes, list, dict, set)):
            raise AttributeError(f"attribute '{key}' cannot be set to {type(value).__name__}: must be int/dict/list/etc")

        self._data[key] = _unwrap_stored(self._data, value)
        self.on.changed.emit()

    def set_default(self, **kwargs):
        """"Set the value of any given key if it has not already been set"""
        for k, v in kwargs.items():
            if k not in self._data:
                self._data[k] = v


class StoredState:

    def __init__(self):
        self.parent_type = None
        self.attr_name = None

    def __get__(self, parent, parent_type=None):
        if self.parent_type is None:
            self.parent_type = parent_type
        elif self.parent_type is not parent_type:
            raise RuntimeError("StoredState shared by {} and {}".format(self.parent_type.__name__, parent_type.__name__))

        if parent is None:
            return self

        bound = parent.__dict__.get(self.attr_name)
        if bound is None:
            for attr_name, attr_value in parent_type.__dict__.items():
                if attr_value is self:
                    if self.attr_name and attr_name != self.attr_name:
                        parent_tname = parent_type.__name__
                        raise RuntimeError(f"StoredState shared by {parent_tname}.{self.attr_name} and {parent_tname}.{attr_name}")
                    self.attr_name = attr_name
                    bound = BoundStoredState(parent, attr_name)
                    parent.__dict__[attr_name] = bound
                    break
            else:
                raise RuntimeError("cannot find StoredVariable attribute in type {}".format(parent_type.__name__))

        return bound


def _wrap_stored(parent_data, value):
    t = type(value)
    if t is dict:
        return StoredDict(parent_data, value)
    if t is list:
        return StoredList(parent_data, value)
    if t is set:
        return StoredSet(parent_data, value)
    return value


def _unwrap_stored(parent_data, value):
    t = type(value)
    if t is StoredDict or t is StoredList or t is StoredSet:
        return value._under
    return value


class StoredDict(collections.abc.MutableMapping):

    def __init__(self, stored_data, under):
        self._stored_data = stored_data
        self._under = under

    def __getitem__(self, key):
        return _wrap_stored(self._stored_data, self._under[key])

    def __setitem__(self, key, value):
        self._under[key] = _unwrap_stored(self._stored_data, value)
        self._stored_data.dirty = True

    def __delitem__(self, key):
        del self._under[key]
        self._stored_data.dirty = True

    def __iter__(self):
        return self._under.__iter__()

    def __len__(self):
        return len(self._under)

    def __eq__(self, other):
        if isinstance(other, StoredDict):
            return self._under == other._under
        elif isinstance(other, collections.abc.Mapping):
            return self._under == other
        else:
            return NotImplemented


class StoredList(collections.abc.MutableSequence):

    def __init__(self, stored_data, under):
        self._stored_data = stored_data
        self._under = under

    def __getitem__(self, index):
        return _wrap_stored(self._stored_data, self._under[index])

    def __setitem__(self, index, value):
        self._under[index] = _unwrap_stored(self._stored_data, value)
        self._stored_data.dirty = True

    def __delitem__(self, index):
        del self._under[index]
        self._stored_data.dirty = True

    def __len__(self):
        return len(self._under)

    def insert(self, index, value):
        self._under.insert(index, value)
        self._stored_data.dirty = True

    def append(self, value):
        self._under.append(value)
        self._stored_data.dirty = True

    def __eq__(self, other):
        if isinstance(other, StoredList):
            return self._under == other._under
        elif isinstance(other, collections.abc.Sequence):
            return self._under == other
        else:
            return NotImplemented

    def __lt__(self, other):
        if isinstance(other, StoredList):
            return self._under < other._under
        elif isinstance(other, collections.abc.Sequence):
            return self._under < other
        else:
            return NotImplemented

    def __le__(self, other):
        if isinstance(other, StoredList):
            return self._under <= other._under
        elif isinstance(other, collections.abc.Sequence):
            return self._under <= other
        else:
            return NotImplemented

    def __gt__(self, other):
        if isinstance(other, StoredList):
            return self._under > other._under
        elif isinstance(other, collections.abc.Sequence):
            return self._under > other
        else:
            return NotImplemented

    def __ge__(self, other):
        if isinstance(other, StoredList):
            return self._under >= other._under
        elif isinstance(other, collections.abc.Sequence):
            return self._under >= other
        else:
            return NotImplemented


class StoredSet(collections.abc.MutableSet):

    def __init__(self, stored_data, under):
        self._stored_data = stored_data
        self._under = under

    def add(self, key):
        self._under.add(key)
        self._stored_data.dirty = True

    def discard(self, key):
        self._under.discard(key)
        self._stored_data.dirty = True

    def __contains__(self, key):
        return key in self._under

    def __iter__(self):
        return self._under.__iter__()

    def __len__(self):
        return len(self._under)

    @classmethod
    def _from_iterable(cls, it):
        """Construct an instance of the class from any iterable input.

        Per https://docs.python.org/3/library/collections.abc.html
        if the Set mixin is being used in a class with a different constructor signature,
        you will need to override _from_iterable() with a classmethod that can construct
        new instances from an iterable argument.
        """
        return set(it)

    def __le__(self, other):
        if isinstance(other, StoredSet):
            return self._under <= other._under
        elif isinstance(other, collections.abc.Set):
            return self._under <= other
        else:
            return NotImplemented

    def __ge__(self, other):
        if isinstance(other, StoredSet):
            return self._under >= other._under
        elif isinstance(other, collections.abc.Set):
            return self._under >= other
        else:
            return NotImplemented

    def __eq__(self, other):
        if isinstance(other, StoredSet):
            return self._under == other._under
        elif isinstance(other, collections.abc.Set):
            return self._under == other
        else:
            return NotImplemented
