"""Weak reference support for Python.

This module is an implementation of PEP 205:

http://www.python.org/dev/peps/pep-0205/
"""

# Naming convention: Variables named "wr" are weak reference objects;
# they are called this instead of "ref" to avoid name collisions with
# the module-global ref() function imported from _weakref.

from _weakref import (
 getweakrefcount,
 getweakrefs,
 ref,
 proxy,
 CallableProxyType,
 ProxyType,
 ReferenceType,
 _remove_dead_weakref)

from _weakrefset import WeakSet, _IterationGuard

import _collections_abc # Import after _weakref to avoid circular import.
import sys
import itertools

ProxyTypes = (ProxyType, CallableProxyType)

__all__ = ["ref", "proxy", "getweakrefcount", "getweakrefs",
 "WeakKeyDictionary", "ReferenceType", "ProxyType",
 "CallableProxyType", "ProxyTypes", "WeakValueDictionary",
 "WeakSet", "WeakMethod", "finalize"]


class WeakMethod(ref):
 """
 A custom `weakref.ref` subclass which simulates a weak reference to
 a bound method, working around the lifetime problem of bound methods.
 """

 __slots__ = "_func_ref", "_meth_type", "_alive", "__weakref__"

 def __new__(cls, meth, callback=None):
 try:
 obj = meth.__self__
 func = meth.__func__
 except AttributeError:
 raise TypeError("argument should be a bound method, not {}"
 .format(type(meth))) from None
 def _cb(arg):
 # The self-weakref trick is needed to avoid creating a reference
 # cycle.
 self = self_wr()
 if self._alive:
 self._alive = False
 if callback is not None:
 callback(self)
 self = ref.__new__(cls, obj, _cb)
 self._func_ref = ref(func, _cb)
 self._meth_type = type(meth)
 self._alive = True
 self_wr = ref(self)
 return self

 def __call__(self):
 obj = super().__call__()
 func = self._func_ref()
 if obj is None or func is None:
 return None
 return self._meth_type(func, obj)

 def __eq__(self, other):
 if isinstance(other, WeakMethod):
 if not self._alive or not other._alive:
 return self is other
 return ref.__eq__(self, other) and self._func_ref == other._func_ref
 return False

 def __ne__(self, other):
 if isinstance(other, WeakMethod):
 if not self._alive or not other._alive:
 return self is not other
 return ref.__ne__(self, other) or self._func_ref != other._func_ref
 return True

 __hash__ = ref.__hash__


class WeakValueDictionary(_collections_abc.MutableMapping):
 """Mapping class that references values weakly.

 Entries in the dictionary will be discarded when no strong
 reference to the value exists anymore
 """
 # We inherit the constructor without worrying about the input
 # dictionary; since it uses our .update() method, we get the right
 # checks (if the other dictionary is a WeakValueDictionary,
 # objects are unwrapped on the way out, and we always wrap on the
 # way in).

 def __init__(self, other=(), /, **kw):
 def remove(wr, selfref=ref(self), _atomic_removal=_remove_dead_weakref):
 self = selfref()
 if self is not None:
 if self._iterating:
 self._pending_removals.append(wr.key)
 else:
 # Atomic removal is necessary since this function
 # can be called asynchronously by the GC
 _atomic_removal(self.data, wr.key)
 self._remove = remove
 # A list of keys to be removed
 self._pending_removals = []
 self._iterating = set()
 self.data = {}
 self.update(other, **kw)

 def _commit_removals(self):
 l = self._pending_removals
 d = self.data
 # We shouldn't encounter any KeyError, because this method should
 # always be called *before* mutating the dict.
 while l:
 key = l.pop()
 _remove_dead_weakref(d, key)

 def __getitem__(self, key):
 if self._pending_removals:
 self._commit_removals()
 o = self.data[key]()
 if o is None:
 raise KeyError(key)
 else:
 return o

 def __delitem__(self, key):
 if self._pending_removals:
 self._commit_removals()
 del self.data[key]

 def __len__(self):
 if self._pending_removals:
 self._commit_removals()
 return len(self.data)

 def __contains__(self, key):
 if self._pending_removals:
 self._commit_removals()
 try:
 o = self.data[key]()
 except KeyError:
 return False
 return o is not None

 def __repr__(self):
 return "<%s at %#x>" % (self.__class__.__name__, id(self))

 def __setitem__(self, key, value):
 if self._pending_removals:
 self._commit_removals()
 self.data[key] = KeyedRef(value, self._remove, key)

 def copy(self):
 if self._pending_removals:
 self._commit_removals()
 new = WeakValueDictionary()
 with _IterationGuard(self):
 for key, wr in self.data.items():
 o = wr()
 if o is not None:
 new[key] = o
 return new

 __copy__ = copy

 def __deepcopy__(self, memo):
 from copy import deepcopy
 if self._pending_removals:
 self._commit_removals()
 new = self.__class__()
 with _IterationGuard(self):
 for key, wr in self.data.items():
 o = wr()
 if o is not None:
 new[deepcopy(key, memo)] = o
 return new

 def get(self, key, default=None):
 if self._pending_removals:
 self._commit_removals()
 try:
 wr = self.data[key]
 except KeyError:
 return default
 else:
 o = wr()
 if o is None:
 # This should only happen
 return default
 else:
 return o

 def items(self):
 if self._pending_removals:
 self._commit_removals()
 with _IterationGuard(self):
 for k, wr in self.data.items():
 v = wr()
 if v is not None:
 yield k, v

 def keys(self):
 if self._pending_removals:
 self._commit_removals()
 with _IterationGuard(self):
 for k, wr in self.data.items():
 if wr() is not None:
 yield k

 __iter__ = keys

 def itervaluerefs(self):
 """Return an iterator that yields the weak references to the values.

 The references are not guaranteed to be 'live' at the time
 they are used, so the result of calling the references needs
 to be checked before being used. This can be used to avoid
 creating references that will cause the garbage collector to
 keep the values around longer than needed.

 """
 if self._pending_removals:
 self._commit_removals()
 with _IterationGuard(self):
 yield from self.data.values()

 def values(self):
 if self._pending_removals:
 self._commit_removals()
 with _IterationGuard(self):
 for wr in self.data.values():
 obj = wr()
 if obj is not None:
 yield obj

 def popitem(self):
 if self._pending_removals:
 self._commit_removals()
 while True:
 key, wr = self.data.popitem()
 o = wr()
 if o is not None:
 return key, o

 def pop(self, key, *args):
 if self._pending_removals:
 self._commit_removals()
 try:
 o = self.data.pop(key)()
 except KeyError:
 o = None
 if o is None:
 if args:
 return args[0]
 else:
 raise KeyError(key)
 else:
 return o

 def setdefault(self, key, default=None):
 try:
 o = self.data[key]()
 except KeyError:
 o = None
 if o is None:
 if self._pending_removals:
 self._commit_removals()
 self.data[key] = KeyedRef(default, self._remove, key)
 return default
 else:
 return o

 def update(self, other=None, /, **kwargs):
 if self._pending_removals:
 self._commit_removals()
 d = self.data
 if other is not None:
 if not hasattr(other, "items"):
 other = dict(other)
 for key, o in other.items():
 d[key] = KeyedRef(o, self._remove, key)
 for key, o in kwargs.items():
 d[key] = KeyedRef(o, self._remove, key)

 def valuerefs(self):
 """Return a list of weak references to the values.

 The references are not guaranteed to be 'live' at the time
 they are used, so the result of calling the references needs
 to be checked before being used. This can be used to avoid
 creating references that will cause the garbage collector to
 keep the values around longer than needed.

 """
 if self._pending_removals:
 self._commit_removals()
 return list(self.data.values())


class KeyedRef(ref):
 """Specialized reference that includes a key corresponding to the value.

 This is used in the WeakValueDictionary to avoid having to create
 a function object for each key stored in the mapping. A shared
 callback object can use the 'key' attribute of a KeyedRef instead
 of getting a reference to the key from an enclosing scope.

 """

 __slots__ = "key",

 def __new__(type, ob, callback, key):
 self = ref.__new__(type, ob, callback)
 self.key = key
 return self

 def __init__(self, ob, callback, key):
 super().__init__(ob, callback)


class WeakKeyDictionary(_collections_abc.MutableMapping):
 """ Mapping class that references keys weakly.

 Entries in the dictionary will be discarded when there is no
 longer a strong reference to the key. This can be used to
 associate additional data with an object owned by other parts of
 an application without adding attributes to those objects. This
 can be especially useful with objects that override attribute
 accesses.
 """

 def __init__(self, dict=None):
 self.data = {}
 def remove(k, selfref=ref(self)):
 self = selfref()
 if self is not None:
 if self._iterating:
 self._pending_removals.append(k)
 else:
 del self.data[k]
 self._remove = remove
 # A list of dead weakrefs (keys to be removed)
 self._pending_removals = []
 self._iterating = set()
 self._dirty_len = False
 if dict is not None:
 self.update(dict)

 def _commit_removals(self):
 # NOTE: We don't need to call this method before mutating the dict,
 # because a dead weakref never compares equal to a live weakref,
 # even if they happened to refer to equal objects.
 # However, it means keys may already have been removed.
 l = self._pending_removals
 d = self.data
 while l:
 try:
 del d[l.pop()]
 except KeyError:
 pass

 def _scrub_removals(self):
 d = self.data
 self._pending_removals = [k for k in self._pending_removals if k in d]
 self._dirty_len = False

 def __delitem__(self, key):
 self._dirty_len = True
 del self.data[ref(key)]

 def __getitem__(self, key):
 return self.data[ref(key)]

 def __len__(self):
 if self._dirty_len and self._pending_removals:
 # self._pending_removals may still contain keys which were
 # explicitly removed, we have to scrub them (see issue #21173).
 self._scrub_removals()
 return len(self.data) - len(self._pending_removals)

 def __repr__(self):
 return "<%s at %#x>" % (self.__class__.__name__, id(self))

 def __setitem__(self, key, value):
 self.data[ref(key, self._remove)] = value

 def copy(self):
 new = WeakKeyDictionary()
 with _IterationGuard(self):
 for key, value in self.data.items():
 o = key()
 if o is not None:
 new[o] = value
 return new

 __copy__ = copy

 def __deepcopy__(self, memo):
 from copy import deepcopy
 new = self.__class__()
 with _IterationGuard(self):
 for key, value in self.data.items():
 o = key()
 if o is not None:
 new[o] = deepcopy(value, memo)
 return new

 def get(self, key, default=None):
 return self.data.get(ref(key),default)

 def __contains__(self, key):
 try:
 wr = ref(key)
 except TypeError:
 return False
 return wr in self.data

 def items(self):
 with _IterationGuard(self):
 for wr, value in self.data.items():
 key = wr()
 if key is not None:
 yield key, value

 def keys(self):
 with _IterationGuard(self):
 for wr in self.data:
 obj = wr()
 if obj is not None:
 yield obj

 __iter__ = keys

 def values(self):
 with _IterationGuard(self):
 for wr, value in self.data.items():
 if wr() is not None:
 yield value

 def keyrefs(self):
 """Return a list of weak references to the keys.

 The references are not guaranteed to be 'live' at the time
 they are used, so the result of calling the references needs
 to be checked before being used. This can be used to avoid
 creating references that will cause the garbage collector to
 keep the keys around longer than needed.

 """
 return list(self.data)

 def popitem(self):
 self._dirty_len = True
 while True:
 key, value = self.data.popitem()
 o = key()
 if o is not None:
 return o, value

 def pop(self, key, *args):
 self._dirty_len = True
 return self.data.pop(ref(key), *args)

 def setdefault(self, key, default=None):
 return self.data.setdefault(ref(key, self._remove),default)

 def update(self, dict=None, /, **kwargs):
 d = self.data
 if dict is not None:
 if not hasattr(dict, "items"):
 dict = type({})(dict)
 for key, value in dict.items():
 d[ref(key, self._remove)] = value
 if len(kwargs):
 self.update(kwargs)


class finalize:
 """Class for finalization of weakrefable objects

 finalize(obj, func, *args, **kwargs) returns a callable finalizer
 object which will be called when obj is garbage collected. The
 first time the finalizer is called it evaluates func(*arg, **kwargs)
 and returns the result. After this the finalizer is dead, and
 calling it just returns None.

 When the program exits any remaining finalizers for which the
 atexit attribute is true will be run in reverse order of creation.
 By default atexit is true.
 """

 # Finalizer objects don't have any state of their own. They are
 # just used as keys to lookup _Info objects in the registry. This
 # ensures that they cannot be part of a ref-cycle.

 __slots__ = ()
 _registry = {}
 _shutdown = False
 _index_iter = itertools.count()
 _dirty = False
 _registered_with_atexit = False

 class _Info:
 __slots__ = ("weakref", "func", "args", "kwargs", "atexit", "index")

 def __init__(*args, **kwargs):
 if len(args) >= 3:
 self, obj, func, *args = args
 elif not args:
 raise TypeError("descriptor '__init__' of 'finalize' object "
 "needs an argument")
 else:
 if 'func' not in kwargs:
 raise TypeError('finalize expected at least 2 positional '
 'arguments, got %d' % (len(args)-1))
 func = kwargs.pop('func')
 if len(args) >= 2:
 self, obj, *args = args
 import warnings
 warnings.warn("Passing 'func' as keyword argument is deprecated",
 DeprecationWarning, stacklevel=2)
 else:
 if 'obj' not in kwargs:
 raise TypeError('finalize expected at least 2 positional '
 'arguments, got %d' % (len(args)-1))
 obj = kwargs.pop('obj')
 self, *args = args
 import warnings
 warnings.warn("Passing 'obj' as keyword argument is deprecated",
 DeprecationWarning, stacklevel=2)
 args = tuple(args)

 if not self._registered_with_atexit:
 # We may register the exit function more than once because
 # of a thread race, but that is harmless
 import atexit
 atexit.register(self._exitfunc)
 finalize._registered_with_atexit = True
 info = self._Info()
 info.weakref = ref(obj, self)
 info.func = func
 info.args = args
 info.kwargs = kwargs or None
 info.atexit = True
 info.index = next(self._index_iter)
 self._registry[self] = info
 finalize._dirty = True
 __init__.__text_signature__ = '($self, obj, func, /, *args, **kwargs)'

 def __call__(self, _=None):
 """If alive then mark as dead and return func(*args, **kwargs);
 otherwise return None"""
 info = self._registry.pop(self, None)
 if info and not self._shutdown:
 return info.func(*info.args, **(info.kwargs or {}))

 def detach(self):
 """If alive then mark as dead and return (obj, func, args, kwargs);
 otherwise return None"""
 info = self._registry.get(self)
 obj = info and info.weakref()
 if obj is not None and self._registry.pop(self, None):
 return (obj, info.func, info.args, info.kwargs or {})

 def peek(self):
 """If alive then return (obj, func, args, kwargs);
 otherwise return None"""
 info = self._registry.get(self)
 obj = info and info.weakref()
 if obj is not None:
 return (obj, info.func, info.args, info.kwargs or {})

 @property
 def alive(self):
 """Whether finalizer is alive"""
 return self in self._registry

 @property
 def atexit(self):
 """Whether finalizer should be called at exit"""
 info = self._registry.get(self)
 return bool(info) and info.atexit

 @atexit.setter
 def atexit(self, value):
 info = self._registry.get(self)
 if info:
 info.atexit = bool(value)

 def __repr__(self):
 info = self._registry.get(self)
 obj = info and info.weakref()
 if obj is None:
 return '<%s object at %#x; dead>' % (type(self).__name__, id(self))
 else:
 return '<%s object at %#x; for %r at %#x>' % \
 (type(self).__name__, id(self), type(obj).__name__, id(obj))

 @classmethod
 def _select_for_exit(cls):
 # Return live finalizers marked for exit, oldest first
 L = [(f,i) for (f,i) in cls._registry.items() if i.atexit]
 L.sort(key=lambda item:item[1].index)
 return [f for (f,i) in L]

 @classmethod
 def _exitfunc(cls):
 # At shutdown invoke finalizers for which atexit is true.
 # This is called once all other non-daemonic threads have been
 # joined.
 reenable_gc = False
 try:
 if cls._registry:
 import gc
 if gc.isenabled():
 reenable_gc = True
 gc.disable()
 pending = None
 while True:
 if pending is None or finalize._dirty:
 pending = cls._select_for_exit()
 finalize._dirty = False
 if not pending:
 break
 f = pending.pop()
 try:
 # gc is disabled, so (assuming no daemonic
 # threads) the following is the only line in
 # this function which might trigger creation
 # of a new finalizer
 f()
 except Exception:
 sys.excepthook(*sys.exc_info())
 assert f not in cls._registry
 finally:
 # prevent any more finalizers from executing during shutdown
 finalize._shutdown = True
 if reenable_gc:
 gc.enable()