##############################################################################
#
# Copyright (c) 2004 Zope Foundation and Contributors.
# All Rights Reserved.
#
# This software is subject to the provisions of the Zope Public License,
# Version 2.1 (ZPL).  A copy of the ZPL should accompany this distribution.
# THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED
# WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
# WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS
# FOR A PARTICULAR PURPOSE.
#
##############################################################################
"""Adapter management
"""
import itertools
import weakref

from zope.interface import implementer
from zope.interface import providedBy
from zope.interface import Interface
from zope.interface import ro
from zope.interface.interfaces import IAdapterRegistry

from zope.interface._compat import _normalize_name
from zope.interface._compat import STRING_TYPES
from zope.interface._compat import _use_c_impl

__all__ = [
    'AdapterRegistry',
    'VerifyingAdapterRegistry',
]

# In the CPython implementation,
# ``tuple`` and ``list`` cooperate so that ``tuple([some list])``
# directly allocates and iterates at the C level without using a
# Python iterator. That's not the case for
# ``tuple(generator_expression)`` or ``tuple(map(func, it))``.
##
# 3.8
# ``tuple([t for t in range(10)])``      -> 610ns
# ``tuple(t for t in range(10))``        -> 696ns
# ``tuple(map(lambda t: t, range(10)))`` -> 881ns
##
# 2.7
# ``tuple([t fon t in range(10)])``      -> 625ns
# ``tuple(t for t in range(10))``        -> 665ns
# ``tuple(map(lambda t: t, range(10)))`` -> 958ns
#
# All three have substantial variance.
##
# On PyPy, this is also the best option.
##
# PyPy 2.7.18-7.3.3
# ``tuple([t fon t in range(10)])``      -> 128ns
# ``tuple(t for t in range(10))``        -> 175ns
# ``tuple(map(lambda t: t, range(10)))`` -> 153ns
##
# PyPy 3.7.9 7.3.3-beta
# ``tuple([t fon t in range(10)])``      ->  82ns
# ``tuple(t for t in range(10))``        -> 177ns
# ``tuple(map(lambda t: t, range(10)))`` -> 168ns
#

class BaseAdapterRegistry(object):
    """
    A basic implementation of the data storage and algorithms required
    for a :class:`zope.interface.interfaces.IAdapterRegistry`.

    Subclasses can set the following attributes to control how the data
    is stored; in particular, these hooks can be helpful for ZODB
    persistence. They can be class attributes that are the named (or similar) type, or
    they can be methods that act as a constructor for an object that behaves
    like the types defined here; this object will not assume that they are type
    objects, but subclasses are free to do so:

    _sequenceType = list
      This is the type used for our two mutable top-level "byorder" sequences.
      Must support mutation operations like ``append()`` and ``del seq[index]``.
      These are usually small (< 10). Although at least one of them is
      accessed when performing lookups or queries on this object, the other
      is untouched. In many common scenarios, both are only required when
      mutating registrations and subscriptions (like what
      :meth:`zope.interface.interfaces.IComponents.registerUtility` does).
      This use pattern makes it an ideal candidate to be a
      :class:`~persistent.list.PersistentList`.
    _leafSequenceType = tuple
      This is the type used for the leaf sequences of subscribers.
      It could be set to a ``PersistentList`` to avoid many unnecessary data
      loads when subscribers aren't being used. Mutation operations are directed
      through :meth:`_addValueToLeaf` and :meth:`_removeValueFromLeaf`; if you use
      a mutable type, you'll need to override those.
    _mappingType = dict
      This is the mutable mapping type used for the keyed mappings.
      A :class:`~persistent.mapping.PersistentMapping`
      could be used to help reduce the number of data loads when the registry is large
      and parts of it are rarely used. Further reductions in data loads can come from
      using a :class:`~BTrees.OOBTree.OOBTree`, but care is required
      to be sure that all required/provided
      values are fully ordered (e.g., no required or provided values that are classes
      can be used).
    _providedType = dict
      This is the mutable mapping type used for the ``_provided`` mapping.
      This is separate from the generic mapping type because the values
      are always integers, so one might choose to use a more optimized data
      structure such as a :class:`~BTrees.OIBTree.OIBTree`.
      The same caveats regarding key types
      apply as for ``_mappingType``.

    It is possible to also set these on an instance, but because of the need to
    potentially also override :meth:`_addValueToLeaf` and :meth:`_removeValueFromLeaf`,
    this may be less useful in a persistent scenario; using a subclass is recommended.

    .. versionchanged:: 5.3.0
        Add support for customizing the way internal data
        structures are created.
    .. versionchanged:: 5.3.0
        Add methods :meth:`rebuild`, :meth:`allRegistrations`
        and :meth:`allSubscriptions`.
    """

    # List of methods copied from lookup sub-objects:
    _delegated = ('lookup', 'queryMultiAdapter', 'lookup1', 'queryAdapter',
                  'adapter_hook', 'lookupAll', 'names',
                  'subscriptions', 'subscribers')

    # All registries maintain a generation that can be used by verifying
    # registries
    _generation = 0

    def __init__(self, bases=()):

        # The comments here could be improved. Possibly this bit needs
        # explaining in a separate document, as the comments here can
        # be quite confusing. /regebro

        # {order -> {required -> {provided -> {name -> value}}}}
        # Here "order" is actually an index in a list, "required" and
        # "provided" are interfaces, and "required" is really a nested
        # key.  So, for example:
        # for order == 0 (that is, self._adapters[0]), we have:
        #   {provided -> {name -> value}}
        # but for order == 2 (that is, self._adapters[2]), we have:
        #   {r1 -> {r2 -> {provided -> {name -> value}}}}
        #
        self._adapters = self._sequenceType()

        # {order -> {required -> {provided -> {name -> [value]}}}}
        # where the remarks about adapters above apply
        self._subscribers = self._sequenceType()

        # Set, with a reference count, keeping track of the interfaces
        # for which we have provided components:
        self._provided = self._providedType()

        # Create ``_v_lookup`` object to perform lookup.  We make this a
        # separate object to to make it easier to implement just the
        # lookup functionality in C.  This object keeps track of cache
        # invalidation data in two kinds of registries.

        #   Invalidating registries have caches that are invalidated
        #     when they or their base registies change.  An invalidating
        #     registry can only have invalidating registries as bases.
        #     See LookupBaseFallback below for the pertinent logic.

        #   Verifying registies can't rely on getting invalidation messages,
        #     so have to check the generations of base registries to determine
        #     if their cache data are current.  See VerifyingBasePy below
        #     for the pertinent object.
        self._createLookup()

        # Setting the bases causes the registries described above
        # to be initialized (self._setBases -> self.changed ->
        # self._v_lookup.changed).

        self.__bases__ = bases

    def _setBases(self, bases):
        """
        If subclasses need to track when ``__bases__`` changes, they
        can override this method.

        Subclasses must still call this method.
        """
        self.__dict__['__bases__'] = bases
        self.ro = ro.ro(self)
        self.changed(self)

    __bases__ = property(lambda self: self.__dict__['__bases__'],
                         lambda self, bases: self._setBases(bases),
                         )

    def _createLookup(self):
        self._v_lookup = self.LookupClass(self)
        for name in self._delegated:
            self.__dict__[name] = getattr(self._v_lookup, name)

    # Hooks for subclasses to define the types of objects used in
    # our data structures.
    # These have to be documented in the docstring, instead of local
    # comments, because Sphinx autodoc ignores the comment and just writes
    # "alias of list"
    _sequenceType = list
    _leafSequenceType = tuple
    _mappingType = dict
    _providedType = dict

    def _addValueToLeaf(self, existing_leaf_sequence, new_item):
        """
        Add the value *new_item* to the *existing_leaf_sequence*, which may
        be ``None``.

        Subclasses that redefine `_leafSequenceType` should override this method.

        :param existing_leaf_sequence:
            If *existing_leaf_sequence* is not *None*, it will be an instance
            of `_leafSequenceType`. (Unless the object has been unpickled
            from an old pickle and the class definition has changed, in which case
            it may be an instance of a previous definition, commonly a `tuple`.)

        :return:
           This method returns the new value to be stored. It may mutate the
           sequence in place if it was not ``None`` and the type is mutable, but
           it must also return it.

        .. versionadded:: 5.3.0
        """
        if existing_leaf_sequence is None:
            return (new_item,)
        return existing_leaf_sequence + (new_item,)

    def _removeValueFromLeaf(self, existing_leaf_sequence, to_remove):
        """
        Remove the item *to_remove* from the (non-``None``, non-empty)
        *existing_leaf_sequence* and return the mutated sequence.

        If there is more than one item that is equal to *to_remove*
        they must all be removed.

        Subclasses that redefine `_leafSequenceType` should override
        this method. Note that they can call this method to help
        in their implementation; this implementation will always
        return a new tuple constructed by iterating across
        the *existing_leaf_sequence* and omitting items equal to *to_remove*.

        :param existing_leaf_sequence:
           As for `_addValueToLeaf`, probably an instance of
           `_leafSequenceType` but possibly an older type; never `None`.
        :return:
           A version of *existing_leaf_sequence* with all items equal to
           *to_remove* removed. Must not return `None`. However,
           returning an empty
           object, even of another type such as the empty tuple, ``()`` is
           explicitly allowed; such an object will never be stored.

        .. versionadded:: 5.3.0
        """
        return tuple([v for v in existing_leaf_sequence if v != to_remove])

    def changed(self, originally_changed):
        self._generation += 1
        self._v_lookup.changed(originally_changed)

    def register(self, required, provided, name, value):
        if not isinstance(name, STRING_TYPES):
            raise ValueError('name is not a string')
        if value is None:
            self.unregister(required, provided, name, value)
            return

        required = tuple([_convert_None_to_Interface(r) for r in required])
        name = _normalize_name(name)
        order = len(required)
        byorder = self._adapters
        while len(byorder) <= order:
            byorder.append(self._mappingType())
        components = byorder[order]
        key = required + (provided,)

        for k in key:
            d = components.get(k)
            if d is None:
                d = self._mappingType()
                components[k] = d
            components = d

        if components.get(name) is value:
            return

        components[name] = value

        n = self._provided.get(provided, 0) + 1
        self._provided[provided] = n
        if n == 1:
            self._v_lookup.add_extendor(provided)

        self.changed(self)

    def _find_leaf(self, byorder, required, provided, name):
        # Find the leaf value, if any, in the *byorder* list
        # for the interface sequence *required* and the interface
        # *provided*, given the already normalized *name*.
        #
        # If no such leaf value exists, returns ``None``
        required = tuple([_convert_None_to_Interface(r) for r in required])
        order = len(required)
        if len(byorder) <= order:
            return None

        components = byorder[order]
        key = required + (provided,)

        for k in key:
            d = components.get(k)
            if d is None:
                return None
            components = d

        return components.get(name)

    def registered(self, required, provided, name=u''):
        return self._find_leaf(
            self._adapters,
            required,
            provided,
            _normalize_name(name)
        )

    @classmethod
    def _allKeys(cls, components, i, parent_k=()):
        if i == 0:
            for k, v in components.items():
                yield parent_k + (k,), v
        else:
            for k, v in components.items():
                new_parent_k = parent_k + (k,)
                for x, y in cls._allKeys(v, i - 1, new_parent_k):
                    yield x, y

    def _all_entries(self, byorder):
        # Recurse through the mapping levels of the `byorder` sequence,
        # reconstructing a flattened sequence of ``(required, provided, name, value)``
        # tuples that can be used to reconstruct the sequence with the appropriate
        # registration methods.
        #
        # Locally reference the `byorder` data; it might be replaced while
        # this method is running (see ``rebuild``).
        for i, components in enumerate(byorder):
            # We will have *i* levels of dictionaries to go before
            # we get to the leaf.
            for key, value in self._allKeys(components, i + 1):
                assert len(key) == i + 2
                required = key[:i]
                provided = key[-2]
                name = key[-1]
                yield (required, provided, name, value)

    def allRegistrations(self):
        """
        Yields tuples ``(required, provided, name, value)`` for all
        the registrations that this object holds.

        These tuples could be passed as the arguments to the
        :meth:`register` method on another adapter registry to
        duplicate the registrations this object holds.

        .. versionadded:: 5.3.0
        """
        for t in self._all_entries(self._adapters):
            yield t

    def unregister(self, required, provided, name, value=None):
        required = tuple([_convert_None_to_Interface(r) for r in required])
        order = len(required)
        byorder = self._adapters
        if order >= len(byorder):
            return False
        components = byorder[order]
        key = required + (provided,)

        # Keep track of how we got to `components`:
        lookups = []
        for k in key:
            d = components.get(k)
            if d is None:
                return
            lookups.append((components, k))
            components = d

        old = components.get(name)
        if old is None:
            return
        if (value is not None) and (old is not value):
            return

        del components[name]
        if not components:
            # Clean out empty containers, since we don't want our keys
            # to reference global objects (interfaces) unnecessarily.
            # This is often a problem when an interface is slated for
            # removal; a hold-over entry in the registry can make it
            # difficult to remove such interfaces.
            for comp, k in reversed(lookups):
                d = comp[k]
                if d:
                    break
                else:
                    del comp[k]
            while byorder and not byorder[-1]:
                del byorder[-1]
        n = self._provided[provided] - 1
        if n == 0:
            del self._provided[provided]
            self._v_lookup.remove_extendor(provided)
        else:
            self._provided[provided] = n

        self.changed(self)

    def subscribe(self, required, provided, value):
        required = tuple([_convert_None_to_Interface(r) for r in required])
        name = u''
        order = len(required)
        byorder = self._subscribers
        while len(byorder) <= order:
            byorder.append(self._mappingType())
        components = byorder[order]
        key = required + (provided,)

        for k in key:
            d = components.get(k)
            if d is None:
                d = self._mappingType()
                components[k] = d
            components = d

        components[name] = self._addValueToLeaf(components.get(name), value)

        if provided is not None:
            n = self._provided.get(provided, 0) + 1
            self._provided[provided] = n
            if n == 1:
                self._v_lookup.add_extendor(provided)

        self.changed(self)

    def subscribed(self, required, provided, subscriber):
        subscribers = self._find_leaf(
            self._subscribers,
            required,
            provided,
            u''
        ) or ()
        return subscriber if subscriber in subscribers else None

    def allSubscriptions(self):
        """
        Yields tuples ``(required, provided, value)`` for all the
        subscribers that this object holds.

        These tuples could be passed as the arguments to the
        :meth:`subscribe` method on another adapter registry to
        duplicate the registrations this object holds.

        .. versionadded:: 5.3.0
        """
        for required, provided, _name, value in self._all_entries(self._subscribers):
            for v in value:
                yield (required, provided, v)

    def unsubscribe(self, required, provided, value=None):
        required = tuple([_convert_None_to_Interface(r) for r in required])
        order = len(required)
        byorder = self._subscribers
        if order >= len(byorder):
            return
        components = byorder[order]
        key = required + (provided,)

        # Keep track of how we got to `components`:
        lookups = []
        for k in key:
            d = components.get(k)
            if d is None:
                return
            lookups.append((components, k))
            components = d

        old = components.get(u'')
        if not old:
            # this is belt-and-suspenders against the failure of cleanup below
            return  # pragma: no cover
        len_old = len(old)
        if value is None:
            # Removing everything; note that the type of ``new`` won't
            # necessarily match the ``_leafSequenceType``, but that's
            # OK because we're about to delete the entire entry
            # anyway.
            new = ()
        else:
            new = self._removeValueFromLeaf(old, value)
        # ``new`` may be the same object as ``old``, just mutated in place,
        # so we cannot compare it to ``old`` to check for changes. Remove
        # our reference to it now to avoid trying to do so below.
        del old

        if len(new) == len_old:
            # No changes, so nothing could have been removed.
            return

        if new:
            components[u''] = new
        else:
            # Instead of setting components[u''] = new, we clean out
            # empty containers, since we don't want our keys to
            # reference global objects (interfaces) unnecessarily.  This
            # is often a problem when an interface is slated for
            # removal; a hold-over entry in the registry can make it
            # difficult to remove such interfaces.
            del components[u'']
            for comp, k in reversed(lookups):
                d = comp[k]
                if d:
                    break
                else:
                    del comp[k]
            while byorder and not byorder[-1]:
                del byorder[-1]

        if provided is not None:
            n = self._provided[provided] + len(new) - len_old
            if n == 0:
                del self._provided[provided]
                self._v_lookup.remove_extendor(provided)
            else:
                self._provided[provided] = n

        self.changed(self)

    def rebuild(self):
        """
        Rebuild (and replace) all the internal data structures of this
        object.

        This is useful, especially for persistent implementations, if
        you suspect an issue with reference counts keeping interfaces
        alive even though they are no longer used.

        It is also useful if you or a subclass change the data types
        (``_mappingType`` and friends) that are to be used.

        This method replaces all internal data structures with new objects;
        it specifically does not re-use any storage.

        .. versionadded:: 5.3.0
        """

        # Grab the iterators, we're about to discard their data.
        registrations = self.allRegistrations()
        subscriptions = self.allSubscriptions()

        def buffer(it):
            # The generator doesn't actually start running until we
            # ask for its next(), by which time the attributes will change
            # unless we do so before calling __init__.
            try:
                first = next(it)
            except StopIteration:
                return iter(())

            return itertools.chain((first,), it)

        registrations = buffer(registrations)
        subscriptions = buffer(subscriptions)


        # Replace the base data structures as well as _v_lookup.
        self.__init__(self.__bases__)
        # Re-register everything previously registered and subscribed.
        #
        # XXX: This is going to call ``self.changed()`` a lot, all of
        # which is unnecessary (because ``self.__init__`` just
        # re-created those dependent objects and also called
        # ``self.changed()``). Is this a bottleneck that needs fixed?
        # (We could do ``self.changed = lambda _: None`` before
        # beginning and remove it after to disable the presumably expensive
        # part of passing that notification to the change of objects.)
        for args in registrations:
            self.register(*args)
        for args in subscriptions:
            self.subscribe(*args)

    # XXX hack to fake out twisted's use of a private api.  We need to get them
    # to use the new registered method.
    def get(self, _): # pragma: no cover
        class XXXTwistedFakeOut:
            selfImplied = {}
        return XXXTwistedFakeOut


_not_in_mapping = object()

@_use_c_impl
class LookupBase(object):

    def __init__(self):
        self._cache = {}
        self._mcache = {}
        self._scache = {}

    def changed(self, ignored=None):
        self._cache.clear()
        self._mcache.clear()
        self._scache.clear()

    def _getcache(self, provided, name):
        cache = self._cache.get(provided)
        if cache is None:
            cache = {}
            self._cache[provided] = cache
        if name:
            c = cache.get(name)
            if c is None:
                c = {}
                cache[name] = c
            cache = c
        return cache

    def lookup(self, required, provided, name=u'', default=None):
        if not isinstance(name, STRING_TYPES):
            raise ValueError('name is not a string')
        cache = self._getcache(provided, name)
        required = tuple(required)
        if len(required) == 1:
            result = cache.get(required[0], _not_in_mapping)
        else:
            result = cache.get(tuple(required), _not_in_mapping)

        if result is _not_in_mapping:
            result = self._uncached_lookup(required, provided, name)
            if len(required) == 1:
                cache[required[0]] = result
            else:
                cache[tuple(required)] = result

        if result is None:
            return default

        return result

    def lookup1(self, required, provided, name=u'', default=None):
        if not isinstance(name, STRING_TYPES):
            raise ValueError('name is not a string')
        cache = self._getcache(provided, name)
        result = cache.get(required, _not_in_mapping)
        if result is _not_in_mapping:
            return self.lookup((required, ), provided, name, default)

        if result is None:
            return default

        return result

    def queryAdapter(self, object, provided, name=u'', default=None):
        return self.adapter_hook(provided, object, name, default)

    def adapter_hook(self, provided, object, name=u'', default=None):
        if not isinstance(name, STRING_TYPES):
            raise ValueError('name is not a string')
        required = providedBy(object)
        cache = self._getcache(provided, name)
        factory = cache.get(required, _not_in_mapping)
        if factory is _not_in_mapping:
            factory = self.lookup((required, ), provided, name)

        if factory is not None:
            if isinstance(object, super):
                object = object.__self__
            result = factory(object)
            if result is not None:
                return result

        return default

    def lookupAll(self, required, provided):
        cache = self._mcache.get(provided)
        if cache is None:
            cache = {}
            self._mcache[provided] = cache

        required = tuple(required)
        result = cache.get(required, _not_in_mapping)
        if result is _not_in_mapping:
            result = self._uncached_lookupAll(required, provided)
            cache[required] = result

        return result


    def subscriptions(self, required, provided):
        cache = self._scache.get(provided)
        if cache is None:
            cache = {}
            self._scache[provided] = cache

        required = tuple(required)
        result = cache.get(required, _not_in_mapping)
        if result is _not_in_mapping:
            result = self._uncached_subscriptions(required, provided)
            cache[required] = result

        return result


@_use_c_impl
class VerifyingBase(LookupBaseFallback):
    # Mixin for lookups against registries which "chain" upwards, and
    # whose lookups invalidate their own caches whenever a parent registry
    # bumps its own '_generation' counter.  E.g., used by
    # zope.component.persistentregistry

    def changed(self, originally_changed):
        LookupBaseFallback.changed(self, originally_changed)
        self._verify_ro = self._registry.ro[1:]
        self._verify_generations = [r._generation for r in self._verify_ro]

    def _verify(self):
        if ([r._generation for r in self._verify_ro]
            != self._verify_generations):
            self.changed(None)

    def _getcache(self, provided, name):
        self._verify()
        return LookupBaseFallback._getcache(self, provided, name)

    def lookupAll(self, required, provided):
        self._verify()
        return LookupBaseFallback.lookupAll(self, required, provided)

    def subscriptions(self, required, provided):
        self._verify()
        return LookupBaseFallback.subscriptions(self, required, provided)


class AdapterLookupBase(object):

    def __init__(self, registry):
        self._registry = registry
        self._required = {}
        self.init_extendors()
        super(AdapterLookupBase, self).__init__()

    def changed(self, ignored=None):
        super(AdapterLookupBase, self).changed(None)
        for r in self._required.keys():
            r = r()
            if r is not None:
                r.unsubscribe(self)
        self._required.clear()


    # Extendors
    # ---------

    # When given an target interface for an adapter lookup, we need to consider
    # adapters for interfaces that extend the target interface.  This is
    # what the extendors dictionary is about.  It tells us all of the
    # interfaces that extend an interface for which there are adapters
    # registered.

    # We could separate this by order and name, thus reducing the
    # number of provided interfaces to search at run time.  The tradeoff,
    # however, is that we have to store more information.  For example,
    # if the same interface is provided for multiple names and if the
    # interface extends many interfaces, we'll have to keep track of
    # a fair bit of information for each name.  It's better to
    # be space efficient here and be time efficient in the cache
    # implementation.

    # TODO: add invalidation when a provided interface changes, in case
    # the interface's __iro__ has changed.  This is unlikely enough that
    # we'll take our chances for now.

    def init_extendors(self):
        self._extendors = {}
        for p in self._registry._provided:
            self.add_extendor(p)

    def add_extendor(self, provided):
        _extendors = self._extendors
        for i in provided.__iro__:
            extendors = _extendors.get(i, ())
            _extendors[i] = (
                [e for e in extendors if provided.isOrExtends(e)]
                +
                [provided]
                +
                [e for e in extendors if not provided.isOrExtends(e)]
                )

    def remove_extendor(self, provided):
        _extendors = self._extendors
        for i in provided.__iro__:
            _extendors[i] = [e for e in _extendors.get(i, ())
                             if e != provided]


    def _subscribe(self, *required):
        _refs = self._required
        for r in required:
            ref = r.weakref()
            if ref not in _refs:
                r.subscribe(self)
                _refs[ref] = 1

    def _uncached_lookup(self, required, provided, name=u''):
        required = tuple(required)
        result = None
        order = len(required)
        for registry in self._registry.ro:
            byorder = registry._adapters
            if order >= len(byorder):
                continue

            extendors = registry._v_lookup._extendors.get(provided)
            if not extendors:
                continue

            components = byorder[order]
            result = _lookup(components, required, extendors, name, 0,
                             order)
            if result is not None:
                break

        self._subscribe(*required)

        return result

    def queryMultiAdapter(self, objects, provided, name=u'', default=None):
        factory = self.lookup([providedBy(o) for o in objects], provided, name)
        if factory is None:
            return default

        result = factory(*[o.__self__ if isinstance(o, super) else o for o in objects])
        if result is None:
            return default

        return result

    def _uncached_lookupAll(self, required, provided):
        required = tuple(required)
        order = len(required)
        result = {}
        for registry in reversed(self._registry.ro):
            byorder = registry._adapters
            if order >= len(byorder):
                continue
            extendors = registry._v_lookup._extendors.get(provided)
            if not extendors:
                continue
            components = byorder[order]
            _lookupAll(components, required, extendors, result, 0, order)

        self._subscribe(*required)

        return tuple(result.items())

    def names(self, required, provided):
        return [c[0] for c in self.lookupAll(required, provided)]

    def _uncached_subscriptions(self, required, provided):
        required = tuple(required)
        order = len(required)
        result = []
        for registry in reversed(self._registry.ro):
            byorder = registry._subscribers
            if order >= len(byorder):
                continue

            if provided is None:
                extendors = (provided, )
            else:
                extendors = registry._v_lookup._extendors.get(provided)
                if extendors is None:
                    continue

            _subscriptions(byorder[order], required, extendors, u'',
                           result, 0, order)

        self._subscribe(*required)

        return result

    def subscribers(self, objects, provided):
        subscriptions = self.subscriptions([providedBy(o) for o in objects], provided)
        if provided is None:
            result = ()
            for subscription in subscriptions:
                subscription(*objects)
        else:
            result = []
            for subscription in subscriptions:
                subscriber = subscription(*objects)
                if subscriber is not None:
                    result.append(subscriber)
        return result

class AdapterLookup(AdapterLookupBase, LookupBase):
    pass

@implementer(IAdapterRegistry)
class AdapterRegistry(BaseAdapterRegistry):
    """
    A full implementation of ``IAdapterRegistry`` that adds support for
    sub-registries.
    """

    LookupClass = AdapterLookup

    def __init__(self, bases=()):
        # AdapterRegisties are invalidating registries, so
        # we need to keep track of our invalidating subregistries.
        self._v_subregistries = weakref.WeakKeyDictionary()

        super(AdapterRegistry, self).__init__(bases)

    def _addSubregistry(self, r):
        self._v_subregistries[r] = 1

    def _removeSubregistry(self, r):
        if r in self._v_subregistries:
            del self._v_subregistries[r]

    def _setBases(self, bases):
        old = self.__dict__.get('__bases__', ())
        for r in old:
            if r not in bases:
                r._removeSubregistry(self)
        for r in bases:
            if r not in old:
                r._addSubregistry(self)

        super(AdapterRegistry, self)._setBases(bases)

    def changed(self, originally_changed):
        super(AdapterRegistry, self).changed(originally_changed)

        for sub in self._v_subregistries.keys():
            sub.changed(originally_changed)


class VerifyingAdapterLookup(AdapterLookupBase, VerifyingBase):
    pass

@implementer(IAdapterRegistry)
class VerifyingAdapterRegistry(BaseAdapterRegistry):
    """
    The most commonly-used adapter registry.
    """

    LookupClass = VerifyingAdapterLookup

def _convert_None_to_Interface(x):
    if x is None:
        return Interface
    else:
        return x

def _lookup(components, specs, provided, name, i, l):
    # this function is called very often.
    # The components.get in loops is executed 100 of 1000s times.
    # by loading get into a local variable the bytecode
    # "LOAD_FAST 0 (components)" in the loop can be eliminated.
    components_get = components.get
    if i < l:
        for spec in specs[i].__sro__:
            comps = components_get(spec)
            if comps:
                r = _lookup(comps, specs, provided, name, i+1, l)
                if r is not None:
                    return r
    else:
        for iface in provided:
            comps = components_get(iface)
            if comps:
                r = comps.get(name)
                if r is not None:
                    return r

    return None

def _lookupAll(components, specs, provided, result, i, l):
    components_get = components.get  # see _lookup above
    if i < l:
        for spec in reversed(specs[i].__sro__):
            comps = components_get(spec)
            if comps:
                _lookupAll(comps, specs, provided, result, i+1, l)
    else:
        for iface in reversed(provided):
            comps = components_get(iface)
            if comps:
                result.update(comps)

def _subscriptions(components, specs, provided, name, result, i, l):
    components_get = components.get  # see _lookup above
    if i < l:
        for spec in reversed(specs[i].__sro__):
            comps = components_get(spec)
            if comps:
                _subscriptions(comps, specs, provided, name, result, i+1, l)
    else:
        for iface in reversed(provided):
            comps = components_get(iface)
            if comps:
                comps = comps.get(name)
                if comps:
                    result.extend(comps)
