New Config: worker_enable_prefetch_count_reduction. 
"""Custom maps, sets, sequences, and other data structures."""
import time
from collections import OrderedDict as _OrderedDict
from collections import deque
from collections.abc import Callable, Mapping, MutableMapping, MutableSet, Sequence
from heapq import heapify, heappop, heappush
from itertools import chain, count
from queue import Empty
from typing import Any, Dict, Iterable, List  # noqa

from .functional import first, uniq
from .text import match_case

try:
    # pypy: dicts are ordered in recent versions
    from __pypy__ import reversed_dict as _dict_is_ordered
except ImportError:
    _dict_is_ordered = None

try:
    from django.utils.functional import LazyObject, LazySettings
except ImportError:
    class LazyObject:
        pass
    LazySettings = LazyObject

__all__ = (
    'AttributeDictMixin', 'AttributeDict', 'BufferMap', 'ChainMap',
    'ConfigurationView', 'DictAttribute', 'Evictable',
    'LimitedSet', 'Messagebuffer', 'OrderedDict',
    'force_mapping', 'lpmerge',
)

REPR_LIMITED_SET = """\
<{name}({size}): maxlen={0.maxlen}, expires={0.expires}, minlen={0.minlen}>\
"""


def force_mapping(m):
    # type: (Any) -> Mapping
    """Wrap object into supporting the mapping interface if necessary."""
    if isinstance(m, (LazyObject, LazySettings)):
        m = m._wrapped
    return DictAttribute(m) if not isinstance(m, Mapping) else m


def lpmerge(L, R):
    # type: (Mapping, Mapping) -> Mapping
    """In place left precedent dictionary merge.

    Keeps values from `L`, if the value in `R` is :const:`None`.
    """
    setitem = L.__setitem__
    [setitem(k, v) for k, v in R.items() if v is not None]
    return L


class OrderedDict(_OrderedDict):
    """Dict where insertion order matters."""

    def _LRUkey(self):
        # type: () -> Any
        # return value of od.keys does not support __next__,
        # but this version will also not create a copy of the list.
        return next(iter(self.keys()))

    if not hasattr(_OrderedDict, 'move_to_end'):
        if _dict_is_ordered:  # pragma: no cover

            def move_to_end(self, key, last=True):
                # type: (Any, bool) -> None
                if not last:
                    # we don't use this argument, and the only way to
                    # implement this on PyPy seems to be O(n): creating a
                    # copy with the order changed, so we just raise.
                    raise NotImplementedError('no last=True on PyPy')
                self[key] = self.pop(key)

        else:

            def move_to_end(self, key, last=True):
                # type: (Any, bool) -> None
                link = self._OrderedDict__map[key]
                link_prev = link[0]
                link_next = link[1]
                link_prev[1] = link_next
                link_next[0] = link_prev
                root = self._OrderedDict__root
                if last:
                    last = root[0]
                    link[0] = last
                    link[1] = root
                    last[1] = root[0] = link
                else:
                    first_node = root[1]
                    link[0] = root
                    link[1] = first_node
                    root[1] = first_node[0] = link


class AttributeDictMixin:
    """Mixin for Mapping interface that adds attribute access.

    I.e., `d.key -> d[key]`).
    """

    def __getattr__(self, k):
        # type: (str) -> Any
        """`d.key -> d[key]`."""
        try:
            return self[k]
        except KeyError:
            raise AttributeError(
                f'{type(self).__name__!r} object has no attribute {k!r}')

    def __setattr__(self, key: str, value) -> None:
        """`d[key] = value -> d.key = value`."""
        self[key] = value


class AttributeDict(dict, AttributeDictMixin):
    """Dict subclass with attribute access."""


class DictAttribute:
    """Dict interface to attributes.

    `obj[k] -> obj.k`
    `obj[k] = val -> obj.k = val`
    """

    obj = None

    def __init__(self, obj):
        # type: (Any) -> None
        object.__setattr__(self, 'obj', obj)

    def __getattr__(self, key):
        # type: (Any) -> Any
        return getattr(self.obj, key)

    def __setattr__(self, key, value):
        # type: (Any, Any) -> None
        return setattr(self.obj, key, value)

    def get(self, key, default=None):
        # type: (Any, Any) -> Any
        try:
            return self[key]
        except KeyError:
            return default

    def setdefault(self, key, default=None):
        # type: (Any, Any) -> None
        if key not in self:
            self[key] = default

    def __getitem__(self, key):
        # type: (Any) -> Any
        try:
            return getattr(self.obj, key)
        except AttributeError:
            raise KeyError(key)

    def __setitem__(self, key, value):
        # type: (Any, Any) -> Any
        setattr(self.obj, key, value)

    def __contains__(self, key):
        # type: (Any) -> bool
        return hasattr(self.obj, key)

    def _iterate_keys(self):
        # type: () -> Iterable
        return iter(dir(self.obj))
    iterkeys = _iterate_keys

    def __iter__(self):
        # type: () -> Iterable
        return self._iterate_keys()

    def _iterate_items(self):
        # type: () -> Iterable
        for key in self._iterate_keys():
            yield key, getattr(self.obj, key)
    iteritems = _iterate_items

    def _iterate_values(self):
        # type: () -> Iterable
        for key in self._iterate_keys():
            yield getattr(self.obj, key)
    itervalues = _iterate_values

    items = _iterate_items
    keys = _iterate_keys
    values = _iterate_values


MutableMapping.register(DictAttribute)


class ChainMap(MutableMapping):
    """Key lookup on a sequence of maps."""

    key_t = None
    changes = None
    defaults = None
    maps = None
    _observers = ()

    def __init__(self, *maps, **kwargs):
        # type: (*Mapping, **Any) -> None
        maps = list(maps or [{}])
        self.__dict__.update(
            key_t=kwargs.get('key_t'),
            maps=maps,
            changes=maps[0],
            defaults=maps[1:],
            _observers=[],
        )

    def add_defaults(self, d):
        # type: (Mapping) -> None
        d = force_mapping(d)
        self.defaults.insert(0, d)
        self.maps.insert(1, d)

    def pop(self, key, *default):
        # type: (Any, *Any) -> Any
        try:
            return self.maps[0].pop(key, *default)
        except KeyError:
            raise KeyError(
                f'Key not found in the first mapping: {key!r}')

    def __missing__(self, key):
        # type: (Any) -> Any
        raise KeyError(key)

    def _key(self, key):
        # type: (Any) -> Any
        return self.key_t(key) if self.key_t is not None else key

    def __getitem__(self, key):
        # type: (Any) -> Any
        _key = self._key(key)
        for mapping in self.maps:
            try:
                return mapping[_key]
            except KeyError:
                pass
        return self.__missing__(key)

    def __setitem__(self, key, value):
        # type: (Any, Any) -> None
        self.changes[self._key(key)] = value

    def __delitem__(self, key):
        # type: (Any) -> None
        try:
            del self.changes[self._key(key)]
        except KeyError:
            raise KeyError(f'Key not found in first mapping: {key!r}')

    def clear(self):
        # type: () -> None
        self.changes.clear()

    def get(self, key, default=None):
        # type: (Any, Any) -> Any
        try:
            return self[self._key(key)]
        except KeyError:
            return default

    def __len__(self):
        # type: () -> int
        return len(set().union(*self.maps))

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

    def __contains__(self, key):
        # type: (Any) -> bool
        key = self._key(key)
        return any(key in m for m in self.maps)

    def __bool__(self):
        # type: () -> bool
        return any(self.maps)
    __nonzero__ = __bool__  # Py2

    def setdefault(self, key, default=None):
        # type: (Any, Any) -> None
        key = self._key(key)
        if key not in self:
            self[key] = default

    def update(self, *args, **kwargs):
        # type: (*Any, **Any) -> Any
        result = self.changes.update(*args, **kwargs)
        for callback in self._observers:
            callback(*args, **kwargs)
        return result

    def __repr__(self):
        # type: () -> str
        return '{0.__class__.__name__}({1})'.format(
            self, ', '.join(map(repr, self.maps)))

    @classmethod
    def fromkeys(cls, iterable, *args):
        # type: (type, Iterable, *Any) -> 'ChainMap'
        """Create a ChainMap with a single dict created from the iterable."""
        return cls(dict.fromkeys(iterable, *args))

    def copy(self):
        # type: () -> 'ChainMap'
        return self.__class__(self.maps[0].copy(), *self.maps[1:])
    __copy__ = copy  # Py2

    def _iter(self, op):
        # type: (Callable) -> Iterable
        # defaults must be first in the stream, so values in
        # changes take precedence.
        # pylint: disable=bad-reversed-sequence
        #   Someone should teach pylint about properties.
        return chain(*(op(d) for d in reversed(self.maps)))

    def _iterate_keys(self):
        # type: () -> Iterable
        return uniq(self._iter(lambda d: d.keys()))
    iterkeys = _iterate_keys

    def _iterate_items(self):
        # type: () -> Iterable
        return ((key, self[key]) for key in self)
    iteritems = _iterate_items

    def _iterate_values(self):
        # type: () -> Iterable
        return (self[key] for key in self)
    itervalues = _iterate_values

    def bind_to(self, callback):
        self._observers.append(callback)

    keys = _iterate_keys
    items = _iterate_items
    values = _iterate_values


class ConfigurationView(ChainMap, AttributeDictMixin):
    """A view over an applications configuration dictionaries.

    Custom (but older) version of :class:`collections.ChainMap`.

    If the key does not exist in ``changes``, the ``defaults``
    dictionaries are consulted.

    Arguments:
        changes (Mapping): Map of configuration changes.
        defaults (List[Mapping]): List of dictionaries containing
            the default configuration.
    """

    def __init__(self, changes, defaults=None, keys=None, prefix=None):
        # type: (Mapping, Mapping, List[str], str) -> None
        defaults = [] if defaults is None else defaults
        super().__init__(changes, *defaults)
        self.__dict__.update(
            prefix=prefix.rstrip('_') + '_' if prefix else prefix,
            _keys=keys,
        )

    def _to_keys(self, key):
        # type: (str) -> Sequence[str]
        prefix = self.prefix
        if prefix:
            pkey = prefix + key if not key.startswith(prefix) else key
            return match_case(pkey, prefix), key
        return key,

    def __getitem__(self, key):
        # type: (str) -> Any
        keys = self._to_keys(key)
        getitem = super().__getitem__
        for k in keys + (
                tuple(f(key) for f in self._keys) if self._keys else ()):
            try:
                return getitem(k)
            except KeyError:
                pass
        try:
            # support subclasses implementing __missing__
            return self.__missing__(key)
        except KeyError:
            if len(keys) > 1:
                raise KeyError(
                    'Key not found: {0!r} (with prefix: {0!r})'.format(*keys))
            raise

    def __setitem__(self, key, value):
        # type: (str, Any) -> Any
        self.changes[self._key(key)] = value

    def first(self, *keys):
        # type: (*str) -> Any
        return first(None, (self.get(key) for key in keys))

    def get(self, key, default=None):
        # type: (str, Any) -> Any
        try:
            return self[key]
        except KeyError:
            return default

    def clear(self):
        # type: () -> None
        """Remove all changes, but keep defaults."""
        self.changes.clear()

    def __contains__(self, key):
        # type: (str) -> bool
        keys = self._to_keys(key)
        return any(any(k in m for k in keys) for m in self.maps)

    def swap_with(self, other):
        # type: (ConfigurationView) -> None
        changes = other.__dict__['changes']
        defaults = other.__dict__['defaults']
        self.__dict__.update(
            changes=changes,
            defaults=defaults,
            key_t=other.__dict__['key_t'],
            prefix=other.__dict__['prefix'],
            maps=[changes] + defaults
        )


class LimitedSet:
    """Kind-of Set (or priority queue) with limitations.

    Good for when you need to test for membership (`a in set`),
    but the set should not grow unbounded.

    ``maxlen`` is enforced at all times, so if the limit is reached
    we'll also remove non-expired items.

    You can also configure ``minlen``: this is the minimal residual size
    of the set.

    All arguments are optional, and no limits are enabled by default.

    Arguments:
        maxlen (int): Optional max number of items.
            Adding more items than ``maxlen`` will result in immediate
            removal of items sorted by oldest insertion time.

        expires (float): TTL for all items.
            Expired items are purged as keys are inserted.

        minlen (int): Minimal residual size of this set.
            .. versionadded:: 4.0

            Value must be less than ``maxlen`` if both are configured.

            Older expired items will be deleted, only after the set
            exceeds ``minlen`` number of items.

        data (Sequence): Initial data to initialize set with.
            Can be an iterable of ``(key, value)`` pairs,
            a dict (``{key: insertion_time}``), or another instance
            of :class:`LimitedSet`.

    Example:
        >>> s = LimitedSet(maxlen=50000, expires=3600, minlen=4000)
        >>> for i in range(60000):
        ...     s.add(i)
        ...     s.add(str(i))
        ...
        >>> 57000 in s  # last 50k inserted values are kept
        True
        >>> '10' in s  # '10' did expire and was purged from set.
        False
        >>> len(s)  # maxlen is reached
        50000
        >>> s.purge(now=time.monotonic() + 7200)  # clock + 2 hours
        >>> len(s)  # now only minlen items are cached
        4000
        >>>> 57000 in s  # even this item is gone now
        False
    """

    max_heap_percent_overload = 15

    def __init__(self, maxlen=0, expires=0, data=None, minlen=0):
        # type: (int, float, Mapping, int) -> None
        self.maxlen = 0 if maxlen is None else maxlen
        self.minlen = 0 if minlen is None else minlen
        self.expires = 0 if expires is None else expires
        self._data = {}
        self._heap = []

        if data:
            # import items from data
            self.update(data)

        if not self.maxlen >= self.minlen >= 0:
            raise ValueError(
                'minlen must be a positive number, less or equal to maxlen.')
        if self.expires < 0:
            raise ValueError('expires cannot be negative!')

    def _refresh_heap(self):
        # type: () -> None
        """Time consuming recreating of heap.  Don't run this too often."""
        self._heap[:] = [entry for entry in self._data.values()]
        heapify(self._heap)

    def _maybe_refresh_heap(self):
        # type: () -> None
        if self._heap_overload >= self.max_heap_percent_overload:
            self._refresh_heap()

    def clear(self):
        # type: () -> None
        """Clear all data, start from scratch again."""
        self._data.clear()
        self._heap[:] = []

    def add(self, item, now=None):
        # type: (Any, float) -> None
        """Add a new item, or reset the expiry time of an existing item."""
        now = now or time.monotonic()
        if item in self._data:
            self.discard(item)
        entry = (now, item)
        self._data[item] = entry
        heappush(self._heap, entry)
        if self.maxlen and len(self._data) >= self.maxlen:
            self.purge()

    def update(self, other):
        # type: (Iterable) -> None
        """Update this set from other LimitedSet, dict or iterable."""
        if not other:
            return
        if isinstance(other, LimitedSet):
            self._data.update(other._data)
            self._refresh_heap()
            self.purge()
        elif isinstance(other, dict):
            # revokes are sent as a dict
            for key, inserted in other.items():
                if isinstance(inserted, (tuple, list)):
                    # in case someone uses ._data directly for sending update
                    inserted = inserted[0]
                if not isinstance(inserted, float):
                    raise ValueError(
                        'Expecting float timestamp, got type '
                        f'{type(inserted)!r} with value: {inserted}')
                self.add(key, inserted)
        else:
            # XXX AVOID THIS, it could keep old data if more parties
            # exchange them all over and over again
            for obj in other:
                self.add(obj)

    def discard(self, item):
        # type: (Any) -> None
        # mark an existing item as removed.  If KeyError is not found, pass.
        self._data.pop(item, None)
        self._maybe_refresh_heap()
    pop_value = discard

    def purge(self, now=None):
        # type: (float) -> None
        """Check oldest items and remove them if needed.

        Arguments:
            now (float): Time of purging -- by default right now.
                This can be useful for unit testing.
        """
        now = now or time.monotonic()
        now = now() if isinstance(now, Callable) else now
        if self.maxlen:
            while len(self._data) > self.maxlen:
                self.pop()
        # time based expiring:
        if self.expires:
            while len(self._data) > self.minlen >= 0:
                inserted_time, _ = self._heap[0]
                if inserted_time + self.expires > now:
                    break  # oldest item hasn't expired yet
                self.pop()

    def pop(self, default: Any = None) -> Any:
        """Remove and return the oldest item, or :const:`None` when empty."""
        while self._heap:
            _, item = heappop(self._heap)
            try:
                self._data.pop(item)
            except KeyError:
                pass
            else:
                return item
        return default

    def as_dict(self):
        # type: () -> Dict
        """Whole set as serializable dictionary.

        Example:
            >>> s = LimitedSet(maxlen=200)
            >>> r = LimitedSet(maxlen=200)
            >>> for i in range(500):
            ...     s.add(i)
            ...
            >>> r.update(s.as_dict())
            >>> r == s
            True
        """
        return {key: inserted for inserted, key in self._data.values()}

    def __eq__(self, other):
        # type: (Any) -> bool
        return self._data == other._data

    def __repr__(self):
        # type: () -> str
        return REPR_LIMITED_SET.format(
            self, name=type(self).__name__, size=len(self),
        )

    def __iter__(self):
        # type: () -> Iterable
        return (i for _, i in sorted(self._data.values()))

    def __len__(self):
        # type: () -> int
        return len(self._data)

    def __contains__(self, key):
        # type: (Any) -> bool
        return key in self._data

    def __reduce__(self):
        # type: () -> Any
        return self.__class__, (
            self.maxlen, self.expires, self.as_dict(), self.minlen)

    def __bool__(self):
        # type: () -> bool
        return bool(self._data)
    __nonzero__ = __bool__  # Py2

    @property
    def _heap_overload(self):
        # type: () -> float
        """Compute how much is heap bigger than data [percents]."""
        return len(self._heap) * 100 / max(len(self._data), 1) - 100


MutableSet.register(LimitedSet)


class Evictable:
    """Mixin for classes supporting the ``evict`` method."""

    Empty = Empty

    def evict(self) -> None:
        """Force evict until maxsize is enforced."""
        self._evict(range=count)

    def _evict(self, limit: int = 100, range=range) -> None:
        try:
            [self._evict1() for _ in range(limit)]
        except IndexError:
            pass

    def _evict1(self) -> None:
        if self._evictcount <= self.maxsize:
            raise IndexError()
        try:
            self._pop_to_evict()
        except self.Empty:
            raise IndexError()


class Messagebuffer(Evictable):
    """A buffer of pending messages."""

    Empty = Empty

    def __init__(self, maxsize, iterable=None, deque=deque):
        # type: (int, Iterable, Any) -> None
        self.maxsize = maxsize
        self.data = deque(iterable or [])
        self._append = self.data.append
        self._pop = self.data.popleft
        self._len = self.data.__len__
        self._extend = self.data.extend

    def put(self, item):
        # type: (Any) -> None
        self._append(item)
        self.maxsize and self._evict()

    def extend(self, it):
        # type: (Iterable) -> None
        self._extend(it)
        self.maxsize and self._evict()

    def take(self, *default):
        # type: (*Any) -> Any
        try:
            return self._pop()
        except IndexError:
            if default:
                return default[0]
            raise self.Empty()

    def _pop_to_evict(self):
        # type: () -> None
        return self.take()

    def __repr__(self):
        # type: () -> str
        return f'<{type(self).__name__}: {len(self)}/{self.maxsize}>'

    def __iter__(self):
        # type: () -> Iterable
        while 1:
            try:
                yield self._pop()
            except IndexError:
                break

    def __len__(self):
        # type: () -> int
        return self._len()

    def __contains__(self, item) -> bool:
        return item in self.data

    def __reversed__(self):
        # type: () -> Iterable
        return reversed(self.data)

    def __getitem__(self, index):
        # type: (Any) -> Any
        return self.data[index]

    @property
    def _evictcount(self):
        # type: () -> int
        return len(self)


Sequence.register(Messagebuffer)


class BufferMap(OrderedDict, Evictable):
    """Map of buffers."""

    Buffer = Messagebuffer
    Empty = Empty

    maxsize = None
    total = 0
    bufmaxsize = None

    def __init__(self, maxsize, iterable=None, bufmaxsize=1000):
        # type: (int, Iterable, int) -> None
        super().__init__()
        self.maxsize = maxsize
        self.bufmaxsize = 1000
        if iterable:
            self.update(iterable)
        self.total = sum(len(buf) for buf in self.items())

    def put(self, key, item):
        # type: (Any, Any) -> None
        self._get_or_create_buffer(key).put(item)
        self.total += 1
        self.move_to_end(key)   # least recently used.
        self.maxsize and self._evict()

    def extend(self, key, it):
        # type: (Any, Iterable) -> None
        self._get_or_create_buffer(key).extend(it)
        self.total += len(it)
        self.maxsize and self._evict()

    def take(self, key, *default):
        # type: (Any, *Any) -> Any
        item, throw = None, False
        try:
            buf = self[key]
        except KeyError:
            throw = True
        else:
            try:
                item = buf.take()
                self.total -= 1
            except self.Empty:
                throw = True
            else:
                self.move_to_end(key)  # mark as LRU

        if throw:
            if default:
                return default[0]
            raise self.Empty()
        return item

    def _get_or_create_buffer(self, key):
        # type: (Any) -> Messagebuffer
        try:
            return self[key]
        except KeyError:
            buf = self[key] = self._new_buffer()
            return buf

    def _new_buffer(self):
        # type: () -> Messagebuffer
        return self.Buffer(maxsize=self.bufmaxsize)

    def _LRUpop(self, *default):
        # type: (*Any) -> Any
        return self[self._LRUkey()].take(*default)

    def _pop_to_evict(self):
        # type: () -> None
        for _ in range(100):
            key = self._LRUkey()
            buf = self[key]
            try:
                buf.take()
            except (IndexError, self.Empty):
                # buffer empty, remove it from mapping.
                self.pop(key)
            else:
                # we removed one item
                self.total -= 1
                # if buffer is empty now, remove it from mapping.
                if not len(buf):
                    self.pop(key)
                else:
                    # move to least recently used.
                    self.move_to_end(key)
                break

    def __repr__(self):
        # type: () -> str
        return f'<{type(self).__name__}: {self.total}/{self.maxsize}>'

    @property
    def _evictcount(self):
        # type: () -> int
        return self.total

"""Custom maps, sets, sequences, and other data structures."""
import time
from collections import OrderedDict as _OrderedDict
from collections import deque
from collections.abc import Callable, Mapping, MutableMapping, MutableSet, Sequence
from heapq import heapify, heappop, heappush
from itertools import chain, count
from queue import Empty
from typing import Any, Dict, Iterable, List  # noqa

from .functional import first, uniq
from .text import match_case

try:
    # pypy: dicts are ordered in recent versions
    from __pypy__ import reversed_dict as _dict_is_ordered
except ImportError:
    _dict_is_ordered = None

try:
    from django.utils.functional import LazyObject, LazySettings
except ImportError:
    class LazyObject:
        pass
    LazySettings = LazyObject

__all__ = (
    'AttributeDictMixin', 'AttributeDict', 'BufferMap', 'ChainMap',
    'ConfigurationView', 'DictAttribute', 'Evictable',
    'LimitedSet', 'Messagebuffer', 'OrderedDict',
    'force_mapping', 'lpmerge',
)

REPR_LIMITED_SET = """\
<{name}({size}): maxlen={0.maxlen}, expires={0.expires}, minlen={0.minlen}>\
"""


def force_mapping(m):
    # type: (Any) -> Mapping
    """Wrap object into supporting the mapping interface if necessary."""
    if isinstance(m, (LazyObject, LazySettings)):
        m = m._wrapped
    return DictAttribute(m) if not isinstance(m, Mapping) else m


def lpmerge(L, R):
    # type: (Mapping, Mapping) -> Mapping
    """In place left precedent dictionary merge.

    Keeps values from `L`, if the value in `R` is :const:`None`.
    """
    setitem = L.__setitem__
    [setitem(k, v) for k, v in R.items() if v is not None]
    return L


class OrderedDict(_OrderedDict):
    """Dict where insertion order matters."""

    def _LRUkey(self):
        # type: () -> Any
        # return value of od.keys does not support __next__,
        # but this version will also not create a copy of the list.
        return next(iter(self.keys()))

    if not hasattr(_OrderedDict, 'move_to_end'):
        if _dict_is_ordered:  # pragma: no cover

            def move_to_end(self, key, last=True):
                # type: (Any, bool) -> None
                if not last:
                    # we don't use this argument, and the only way to
                    # implement this on PyPy seems to be O(n): creating a
                    # copy with the order changed, so we just raise.
                    raise NotImplementedError('no last=True on PyPy')
                self[key] = self.pop(key)

        else:

            def move_to_end(self, key, last=True):
                # type: (Any, bool) -> None
                link = self._OrderedDict__map[key]
                link_prev = link[0]
                link_next = link[1]
                link_prev[1] = link_next
                link_next[0] = link_prev
                root = self._OrderedDict__root
                if last:
                    last = root[0]
                    link[0] = last
                    link[1] = root
                    last[1] = root[0] = link
                else:
                    first_node = root[1]
                    link[0] = root
                    link[1] = first_node
                    root[1] = first_node[0] = link


class AttributeDictMixin:
    """Mixin for Mapping interface that adds attribute access.

    I.e., `d.key -> d[key]`).
    """

    def __getattr__(self, k):
        # type: (str) -> Any
        """`d.key -> d[key]`."""
        try:
            return self[k]
        except KeyError:
            raise AttributeError(
                f'{type(self).__name__!r} object has no attribute {k!r}')

    def __setattr__(self, key: str, value) -> None:
        """`d[key] = value -> d.key = value`."""
        self[key] = value


class AttributeDict(dict, AttributeDictMixin):
    """Dict subclass with attribute access."""


class DictAttribute:
    """Dict interface to attributes.

    `obj[k] -> obj.k`
    `obj[k] = val -> obj.k = val`
    """

    obj = None

    def __init__(self, obj):
        # type: (Any) -> None
        object.__setattr__(self, 'obj', obj)

    def __getattr__(self, key):
        # type: (Any) -> Any
        return getattr(self.obj, key)

    def __setattr__(self, key, value):
        # type: (Any, Any) -> None
        return setattr(self.obj, key, value)

    def get(self, key, default=None):
        # type: (Any, Any) -> Any
        try:
            return self[key]
        except KeyError:
            return default

    def setdefault(self, key, default=None):
        # type: (Any, Any) -> None
        if key not in self:
            self[key] = default

    def __getitem__(self, key):
        # type: (Any) -> Any
        try:
            return getattr(self.obj, key)
        except AttributeError:
            raise KeyError(key)

    def __setitem__(self, key, value):
        # type: (Any, Any) -> Any
        setattr(self.obj, key, value)

    def __contains__(self, key):
        # type: (Any) -> bool
        return hasattr(self.obj, key)

    def _iterate_keys(self):
        # type: () -> Iterable
        return iter(dir(self.obj))
    iterkeys = _iterate_keys

    def __iter__(self):
        # type: () -> Iterable
        return self._iterate_keys()

    def _iterate_items(self):
        # type: () -> Iterable
        for key in self._iterate_keys():
            yield key, getattr(self.obj, key)
    iteritems = _iterate_items

    def _iterate_values(self):
        # type: () -> Iterable
        for key in self._iterate_keys():
            yield getattr(self.obj, key)
    itervalues = _iterate_values

    items = _iterate_items
    keys = _iterate_keys
    values = _iterate_values


MutableMapping.register(DictAttribute)


class ChainMap(MutableMapping):
    """Key lookup on a sequence of maps."""

    key_t = None
    changes = None
    defaults = None
    maps = None
    _observers = ()

    def __init__(self, *maps, **kwargs):
        # type: (*Mapping, **Any) -> None
        maps = list(maps or [{}])
        self.__dict__.update(
            key_t=kwargs.get('key_t'),
            maps=maps,
            changes=maps[0],
            defaults=maps[1:],
            _observers=[],
        )

    def add_defaults(self, d):
        # type: (Mapping) -> None
        d = force_mapping(d)
        self.defaults.insert(0, d)
        self.maps.insert(1, d)

    def pop(self, key, *default):
        # type: (Any, *Any) -> Any
        try:
            return self.maps[0].pop(key, *default)
        except KeyError:
            raise KeyError(
                f'Key not found in the first mapping: {key!r}')

    def __missing__(self, key):
        # type: (Any) -> Any
        raise KeyError(key)

    def _key(self, key):
        # type: (Any) -> Any
        return self.key_t(key) if self.key_t is not None else key

    def __getitem__(self, key):
        # type: (Any) -> Any
        _key = self._key(key)
        for mapping in self.maps:
            try:
                return mapping[_key]
            except KeyError:
                pass
        return self.__missing__(key)

    def __setitem__(self, key, value):
        # type: (Any, Any) -> None
        self.changes[self._key(key)] = value

    def __delitem__(self, key):
        # type: (Any) -> None
        try:
            del self.changes[self._key(key)]
        except KeyError:
            raise KeyError(f'Key not found in first mapping: {key!r}')

    def clear(self):
        # type: () -> None
        self.changes.clear()

    def get(self, key, default=None):
        # type: (Any, Any) -> Any
        try:
            return self[self._key(key)]
        except KeyError:
            return default

    def __len__(self):
        # type: () -> int
        return len(set().union(*self.maps))

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

    def __contains__(self, key):
        # type: (Any) -> bool
        key = self._key(key)
        return any(key in m for m in self.maps)

    def __bool__(self):
        # type: () -> bool
        return any(self.maps)
    __nonzero__ = __bool__  # Py2

    def setdefault(self, key, default=None):
        # type: (Any, Any) -> None
        key = self._key(key)
        if key not in self:
            self[key] = default

    def update(self, *args, **kwargs):
        # type: (*Any, **Any) -> Any
        result = self.changes.update(*args, **kwargs)
        for callback in self._observers:
            callback(*args, **kwargs)
        return result

    def __repr__(self):
        # type: () -> str
        return '{0.__class__.__name__}({1})'.format(
            self, ', '.join(map(repr, self.maps)))

    @classmethod
    def fromkeys(cls, iterable, *args):
        # type: (type, Iterable, *Any) -> 'ChainMap'
        """Create a ChainMap with a single dict created from the iterable."""
        return cls(dict.fromkeys(iterable, *args))

    def copy(self):
        # type: () -> 'ChainMap'
        return self.__class__(self.maps[0].copy(), *self.maps[1:])
    __copy__ = copy  # Py2

    def _iter(self, op):
        # type: (Callable) -> Iterable
        # defaults must be first in the stream, so values in
        # changes take precedence.
        # pylint: disable=bad-reversed-sequence
        #   Someone should teach pylint about properties.
        return chain(*(op(d) for d in reversed(self.maps)))

    def _iterate_keys(self):
        # type: () -> Iterable
        return uniq(self._iter(lambda d: d.keys()))
    iterkeys = _iterate_keys

    def _iterate_items(self):
        # type: () -> Iterable
        return ((key, self[key]) for key in self)
    iteritems = _iterate_items

    def _iterate_values(self):
        # type: () -> Iterable
        return (self[key] for key in self)
    itervalues = _iterate_values

    def bind_to(self, callback):
        self._observers.append(callback)

    keys = _iterate_keys
    items = _iterate_items
    values = _iterate_values


class ConfigurationView(ChainMap, AttributeDictMixin):
    """A view over an applications configuration dictionaries.

    Custom (but older) version of :class:`collections.ChainMap`.

    If the key does not exist in ``changes``, the ``defaults``
    dictionaries are consulted.

    Arguments:
        changes (Mapping): Map of configuration changes.
        defaults (List[Mapping]): List of dictionaries containing
            the default configuration.
    """

    def __init__(self, changes, defaults=None, keys=None, prefix=None):
        # type: (Mapping, Mapping, List[str], str) -> None
        defaults = [] if defaults is None else defaults
        super().__init__(changes, *defaults)
        self.__dict__.update(
            prefix=prefix.rstrip('_') + '_' if prefix else prefix,
            _keys=keys,
        )

    def _to_keys(self, key):
        # type: (str) -> Sequence[str]
        prefix = self.prefix
        if prefix:
            pkey = prefix + key if not key.startswith(prefix) else key
            return match_case(pkey, prefix), key
        return key,

    def __getitem__(self, key):
        # type: (str) -> Any
        keys = self._to_keys(key)
        getitem = super().__getitem__
        for k in keys + (
                tuple(f(key) for f in self._keys) if self._keys else ()):
            try:
                return getitem(k)
            except KeyError:
                pass
        try:
            # support subclasses implementing __missing__
            return self.__missing__(key)
        except KeyError:
            if len(keys) > 1:
                raise KeyError(
                    'Key not found: {0!r} (with prefix: {0!r})'.format(*keys))
            raise

    def __setitem__(self, key, value):
        # type: (str, Any) -> Any
        self.changes[self._key(key)] = value

    def first(self, *keys):
        # type: (*str) -> Any
        return first(None, (self.get(key) for key in keys))

    def get(self, key, default=None):
        # type: (str, Any) -> Any
        try:
            return self[key]
        except KeyError:
            return default

    def clear(self):
        # type: () -> None
        """Remove all changes, but keep defaults."""
        self.changes.clear()

    def __contains__(self, key):
        # type: (str) -> bool
        keys = self._to_keys(key)
        return any(any(k in m for k in keys) for m in self.maps)

    def swap_with(self, other):
        # type: (ConfigurationView) -> None
        changes = other.__dict__['changes']
        defaults = other.__dict__['defaults']
        self.__dict__.update(
            changes=changes,
            defaults=defaults,
            key_t=other.__dict__['key_t'],
            prefix=other.__dict__['prefix'],
            maps=[changes] + defaults
        )


class LimitedSet:
    """Kind-of Set (or priority queue) with limitations.

    Good for when you need to test for membership (`a in set`),
    but the set should not grow unbounded.

    ``maxlen`` is enforced at all times, so if the limit is reached
    we'll also remove non-expired items.

    You can also configure ``minlen``: this is the minimal residual size
    of the set.

    All arguments are optional, and no limits are enabled by default.

    Arguments:
        maxlen (int): Optional max number of items.
            Adding more items than ``maxlen`` will result in immediate
            removal of items sorted by oldest insertion time.

        expires (float): TTL for all items.
            Expired items are purged as keys are inserted.

        minlen (int): Minimal residual size of this set.
            .. versionadded:: 4.0

            Value must be less than ``maxlen`` if both are configured.

            Older expired items will be deleted, only after the set
            exceeds ``minlen`` number of items.

        data (Sequence): Initial data to initialize set with.
            Can be an iterable of ``(key, value)`` pairs,
            a dict (``{key: insertion_time}``), or another instance
            of :class:`LimitedSet`.

    Example:
        >>> s = LimitedSet(maxlen=50000, expires=3600, minlen=4000)
        >>> for i in range(60000):
        ...     s.add(i)
        ...     s.add(str(i))
        ...
        >>> 57000 in s  # last 50k inserted values are kept
        True
        >>> '10' in s  # '10' did expire and was purged from set.
        False
        >>> len(s)  # maxlen is reached
        50000
        >>> s.purge(now=time.monotonic() + 7200)  # clock + 2 hours
        >>> len(s)  # now only minlen items are cached
        4000
        >>>> 57000 in s  # even this item is gone now
        False
    """

    max_heap_percent_overload = 15

    def __init__(self, maxlen=0, expires=0, data=None, minlen=0):
        # type: (int, float, Mapping, int) -> None
        self.maxlen = 0 if maxlen is None else maxlen
        self.minlen = 0 if minlen is None else minlen
        self.expires = 0 if expires is None else expires
        self._data = {}
        self._heap = []

        if data:
            # import items from data
            self.update(data)

        if not self.maxlen >= self.minlen >= 0:
            raise ValueError(
                'minlen must be a positive number, less or equal to maxlen.')
        if self.expires < 0:
            raise ValueError('expires cannot be negative!')

    def _refresh_heap(self):
        # type: () -> None
        """Time consuming recreating of heap.  Don't run this too often."""
        self._heap[:] = [entry for entry in self._data.values()]
        heapify(self._heap)

    def _maybe_refresh_heap(self):
        # type: () -> None
        if self._heap_overload >= self.max_heap_percent_overload:
            self._refresh_heap()

    def clear(self):
        # type: () -> None
        """Clear all data, start from scratch again."""
        self._data.clear()
        self._heap[:] = []

    def add(self, item, now=None):
        # type: (Any, float) -> None
        """Add a new item, or reset the expiry time of an existing item."""
        now = now or time.monotonic()
        if item in self._data:
            self.discard(item)
        entry = (now, item)
        self._data[item] = entry
        heappush(self._heap, entry)
        if self.maxlen and len(self._data) >= self.maxlen:
            self.purge()

    def update(self, other):
        # type: (Iterable) -> None
        """Update this set from other LimitedSet, dict or iterable."""
        if not other:
            return
        if isinstance(other, LimitedSet):
            self._data.update(other._data)
            self._refresh_heap()
            self.purge()
        elif isinstance(other, dict):
            # revokes are sent as a dict
            for key, inserted in other.items():
                if isinstance(inserted, (tuple, list)):
                    # in case someone uses ._data directly for sending update
                    inserted = inserted[0]
                if not isinstance(inserted, float):
                    raise ValueError(
                        'Expecting float timestamp, got type '
                        f'{type(inserted)!r} with value: {inserted}')
                self.add(key, inserted)
        else:
            # XXX AVOID THIS, it could keep old data if more parties
            # exchange them all over and over again
            for obj in other:
                self.add(obj)

    def discard(self, item):
        # type: (Any) -> None
        # mark an existing item as removed.  If KeyError is not found, pass.
        self._data.pop(item, None)
        self._maybe_refresh_heap()
    pop_value = discard

    def purge(self, now=None):
        # type: (float) -> None
        """Check oldest items and remove them if needed.

        Arguments:
            now (float): Time of purging -- by default right now.
                This can be useful for unit testing.
        """
        now = now or time.monotonic()
        now = now() if isinstance(now, Callable) else now
        if self.maxlen:
            while len(self._data) > self.maxlen:
                self.pop()
        # time based expiring:
        if self.expires:
            while len(self._data) > self.minlen >= 0:
                inserted_time, _ = self._heap[0]
                if inserted_time + self.expires > now:
                    break  # oldest item hasn't expired yet
                self.pop()

    def pop(self, default: Any = None) -> Any:
        """Remove and return the oldest item, or :const:`None` when empty."""
        while self._heap:
            _, item = heappop(self._heap)
            try:
                self._data.pop(item)
            except KeyError:
                pass
            else:
                return item
        return default

    def as_dict(self):
        # type: () -> Dict
        """Whole set as serializable dictionary.

        Example:
            >>> s = LimitedSet(maxlen=200)
            >>> r = LimitedSet(maxlen=200)
            >>> for i in range(500):
            ...     s.add(i)
            ...
            >>> r.update(s.as_dict())
            >>> r == s
            True
        """
        return {key: inserted for inserted, key in self._data.values()}

    def __eq__(self, other):
        # type: (Any) -> bool
        return self._data == other._data

    def __repr__(self):
        # type: () -> str
        return REPR_LIMITED_SET.format(
            self, name=type(self).__name__, size=len(self),
        )

    def __iter__(self):
        # type: () -> Iterable
        return (i for _, i in sorted(self._data.values()))

    def __len__(self):
        # type: () -> int
        return len(self._data)

    def __contains__(self, key):
        # type: (Any) -> bool
        return key in self._data

    def __reduce__(self):
        # type: () -> Any
        return self.__class__, (
            self.maxlen, self.expires, self.as_dict(), self.minlen)

    def __bool__(self):
        # type: () -> bool
        return bool(self._data)
    __nonzero__ = __bool__  # Py2

    @property
    def _heap_overload(self):
        # type: () -> float
        """Compute how much is heap bigger than data [percents]."""
        return len(self._heap) * 100 / max(len(self._data), 1) - 100


MutableSet.register(LimitedSet)


class Evictable:
    """Mixin for classes supporting the ``evict`` method."""

    Empty = Empty

    def evict(self) -> None:
        """Force evict until maxsize is enforced."""
        self._evict(range=count)

    def _evict(self, limit: int = 100, range=range) -> None:
        try:
            [self._evict1() for _ in range(limit)]
        except IndexError:
            pass

    def _evict1(self) -> None:
        if self._evictcount <= self.maxsize:
            raise IndexError()
        try:
            self._pop_to_evict()
        except self.Empty:
            raise IndexError()


class Messagebuffer(Evictable):
    """A buffer of pending messages."""

    Empty = Empty

    def __init__(self, maxsize, iterable=None, deque=deque):
        # type: (int, Iterable, Any) -> None
        self.maxsize = maxsize
        self.data = deque(iterable or [])
        self._append = self.data.append
        self._pop = self.data.popleft
        self._len = self.data.__len__
        self._extend = self.data.extend

    def put(self, item):
        # type: (Any) -> None
        self._append(item)
        self.maxsize and self._evict()

    def extend(self, it):
        # type: (Iterable) -> None
        self._extend(it)
        self.maxsize and self._evict()

    def take(self, *default):
        # type: (*Any) -> Any
        try:
            return self._pop()
        except IndexError:
            if default:
                return default[0]
            raise self.Empty()

    def _pop_to_evict(self):
        # type: () -> None
        return self.take()

    def __repr__(self):
        # type: () -> str
        return f'<{type(self).__name__}: {len(self)}/{self.maxsize}>'

    def __iter__(self):
        # type: () -> Iterable
        while 1:
            try:
                yield self._pop()
            except IndexError:
                break

    def __len__(self):
        # type: () -> int
        return self._len()

    def __contains__(self, item) -> bool:
        return item in self.data

    def __reversed__(self):
        # type: () -> Iterable
        return reversed(self.data)

    def __getitem__(self, index):
        # type: (Any) -> Any
        return self.data[index]

    @property
    def _evictcount(self):
        # type: () -> int
        return len(self)


Sequence.register(Messagebuffer)


class BufferMap(OrderedDict, Evictable):
    """Map of buffers."""

    Buffer = Messagebuffer
    Empty = Empty

    maxsize = None
    total = 0
    bufmaxsize = None

    def __init__(self, maxsize, iterable=None, bufmaxsize=1000):
        # type: (int, Iterable, int) -> None
        super().__init__()
        self.maxsize = maxsize
        self.bufmaxsize = 1000
        if iterable:
            self.update(iterable)
        self.total = sum(len(buf) for buf in self.items())

    def put(self, key, item):
        # type: (Any, Any) -> None
        self._get_or_create_buffer(key).put(item)
        self.total += 1
        self.move_to_end(key)   # least recently used.
        self.maxsize and self._evict()

    def extend(self, key, it):
        # type: (Any, Iterable) -> None
        self._get_or_create_buffer(key).extend(it)
        self.total += len(it)
        self.maxsize and self._evict()

    def take(self, key, *default):
        # type: (Any, *Any) -> Any
        item, throw = None, False
        try:
            buf = self[key]
        except KeyError:
            throw = True
        else:
            try:
                item = buf.take()
                self.total -= 1
            except self.Empty:
                throw = True
            else:
                self.move_to_end(key)  # mark as LRU

        if throw:
            if default:
                return default[0]
            raise self.Empty()
        return item

    def _get_or_create_buffer(self, key):
        # type: (Any) -> Messagebuffer
        try:
            return self[key]
        except KeyError:
            buf = self[key] = self._new_buffer()
            return buf

    def _new_buffer(self):
        # type: () -> Messagebuffer
        return self.Buffer(maxsize=self.bufmaxsize)

    def _LRUpop(self, *default):
        # type: (*Any) -> Any
        return self[self._LRUkey()].take(*default)

    def _pop_to_evict(self):
        # type: () -> None
        for _ in range(100):
            key = self._LRUkey()
            buf = self[key]
            try:
                buf.take()
            except (IndexError, self.Empty):
                # buffer empty, remove it from mapping.
                self.pop(key)
            else:
                # we removed one item
                self.total -= 1
                # if buffer is empty now, remove it from mapping.
                if not len(buf):
                    self.pop(key)
                else:
                    # move to least recently used.
                    self.move_to_end(key)
                break

    def __repr__(self):
        # type: () -> str
        return f'<{type(self).__name__}: {self.total}/{self.maxsize}>'

    @property
    def _evictcount(self):
        # type: () -> int
        return self.total
