"""Utilities for with-statement contexts. See PEP 343."""
import abc
import sys
import _collections_abc
from collections import deque
from functools import wraps
from types import MethodType

__all__ = ["asynccontextmanager", "contextmanager", "closing", "nullcontext",
 "AbstractContextManager", "AbstractAsyncContextManager",
 "AsyncExitStack", "ContextDecorator", "ExitStack",
 "redirect_stdout", "redirect_stderr", "suppress"]


class AbstractContextManager(abc.ABC):

 """An abstract base class for context managers."""

 def __enter__(self):
 """Return `self` upon entering the runtime context."""
 return self

 @abc.abstractmethod
 def __exit__(self, exc_type, exc_value, traceback):
 """Raise any exception triggered within the runtime context."""
 return None

 @classmethod
 def __subclasshook__(cls, C):
 if cls is AbstractContextManager:
 return _collections_abc._check_methods(C, "__enter__", "__exit__")
 return NotImplemented


class AbstractAsyncContextManager(abc.ABC):

 """An abstract base class for asynchronous context managers."""

 async def __aenter__(self):
 """Return `self` upon entering the runtime context."""
 return self

 @abc.abstractmethod
 async def __aexit__(self, exc_type, exc_value, traceback):
 """Raise any exception triggered within the runtime context."""
 return None

 @classmethod
 def __subclasshook__(cls, C):
 if cls is AbstractAsyncContextManager:
 return _collections_abc._check_methods(C, "__aenter__",
 "__aexit__")
 return NotImplemented


class ContextDecorator(object):
 "A base class or mixin that enables context managers to work as decorators."

 def _recreate_cm(self):
 """Return a recreated instance of self.

 Allows an otherwise one-shot context manager like
 _GeneratorContextManager to support use as
 a decorator via implicit recreation.

 This is a private interface just for _GeneratorContextManager.
 See issue #11647 for details.
 """
 return self

 def __call__(self, func):
 @wraps(func)
 def inner(*args, **kwds):
 with self._recreate_cm():
 return func(*args, **kwds)
 return inner


class _GeneratorContextManagerBase:
 """Shared functionality for @contextmanager and @asynccontextmanager."""

 def __init__(self, func, args, kwds):
 self.gen = func(*args, **kwds)
 self.func, self.args, self.kwds = func, args, kwds
 # Issue 19330: ensure context manager instances have good docstrings
 doc = getattr(func, "__doc__", None)
 if doc is None:
 doc = type(self).__doc__
 self.__doc__ = doc
 # Unfortunately, this still doesn't provide good help output when
 # inspecting the created context manager instances, since pydoc
 # currently bypasses the instance docstring and shows the docstring
 # for the class instead.
 # See http://bugs.python.org/issue19404 for more details.


class _GeneratorContextManager(_GeneratorContextManagerBase,
 AbstractContextManager,
 ContextDecorator):
 """Helper for @contextmanager decorator."""

 def _recreate_cm(self):
 # _GCM instances are one-shot context managers, so the
 # CM must be recreated each time a decorated function is
 # called
 return self.__class__(self.func, self.args, self.kwds)

 def __enter__(self):
 # do not keep args and kwds alive unnecessarily
 # they are only needed for recreation, which is not possible anymore
 del self.args, self.kwds, self.func
 try:
 return next(self.gen)
 except StopIteration:
 raise RuntimeError("generator didn't yield") from None

 def __exit__(self, type, value, traceback):
 if type is None:
 try:
 next(self.gen)
 except StopIteration:
 return False
 else:
 raise RuntimeError("generator didn't stop")
 else:
 if value is None:
 # Need to force instantiation so we can reliably
 # tell if we get the same exception back
 value = type()
 try:
 self.gen.throw(type, value, traceback)
 except StopIteration as exc:
 # Suppress StopIteration *unless* it's the same exception that
 # was passed to throw(). This prevents a StopIteration
 # raised inside the "with" statement from being suppressed.
 return exc is not value
 except RuntimeError as exc:
 # Don't re-raise the passed in exception. (issue27122)
 if exc is value:
 return False
 # Likewise, avoid suppressing if a StopIteration exception
 # was passed to throw() and later wrapped into a RuntimeError
 # (see PEP 479).
 if type is StopIteration and exc.__cause__ is value:
 return False
 raise
 except:
 # only re-raise if it's *not* the exception that was
 # passed to throw(), because __exit__() must not raise
 # an exception unless __exit__() itself failed. But throw()
 # has to raise the exception to signal propagation, so this
 # fixes the impedance mismatch between the throw() protocol
 # and the __exit__() protocol.
 #
 # This cannot use 'except BaseException as exc' (as in the
 # async implementation) to maintain compatibility with
 # Python 2, where old-style class exceptions are not caught
 # by 'except BaseException'.
 if sys.exc_info()[1] is value:
 return False
 raise
 raise RuntimeError("generator didn't stop after throw()")


class _AsyncGeneratorContextManager(_GeneratorContextManagerBase,
 AbstractAsyncContextManager):
 """Helper for @asynccontextmanager."""

 async def __aenter__(self):
 try:
 return await self.gen.__anext__()
 except StopAsyncIteration:
 raise RuntimeError("generator didn't yield") from None

 async def __aexit__(self, typ, value, traceback):
 if typ is None:
 try:
 await self.gen.__anext__()
 except StopAsyncIteration:
 return
 else:
 raise RuntimeError("generator didn't stop")
 else:
 if value is None:
 value = typ()
 # See _GeneratorContextManager.__exit__ for comments on subtleties
 # in this implementation
 try:
 await self.gen.athrow(typ, value, traceback)
 raise RuntimeError("generator didn't stop after athrow()")
 except StopAsyncIteration as exc:
 return exc is not value
 except RuntimeError as exc:
 if exc is value:
 return False
 # Avoid suppressing if a StopIteration exception
 # was passed to throw() and later wrapped into a RuntimeError
 # (see PEP 479 for sync generators; async generators also
 # have this behavior). But do this only if the exception wrapped
 # by the RuntimeError is actully Stop(Async)Iteration (see
 # issue29692).
 if isinstance(value, (StopIteration, StopAsyncIteration)):
 if exc.__cause__ is value:
 return False
 raise
 except BaseException as exc:
 if exc is not value:
 raise


def contextmanager(func):
 """@contextmanager decorator.

 Typical usage:

 @contextmanager
 def some_generator(<arguments>):
 <setup>
 try:
 yield <value>
 finally:
 <cleanup>

 This makes this:

 with some_generator(<arguments>) as <variable>:
 <body>

 equivalent to this:

 <setup>
 try:
 <variable> = <value>
 <body>
 finally:
 <cleanup>
 """
 @wraps(func)
 def helper(*args, **kwds):
 return _GeneratorContextManager(func, args, kwds)
 return helper


def asynccontextmanager(func):
 """@asynccontextmanager decorator.

 Typical usage:

 @asynccontextmanager
 async def some_async_generator(<arguments>):
 <setup>
 try:
 yield <value>
 finally:
 <cleanup>

 This makes this:

 async with some_async_generator(<arguments>) as <variable>:
 <body>

 equivalent to this:

 <setup>
 try:
 <variable> = <value>
 <body>
 finally:
 <cleanup>
 """
 @wraps(func)
 def helper(*args, **kwds):
 return _AsyncGeneratorContextManager(func, args, kwds)
 return helper


class closing(AbstractContextManager):
 """Context to automatically close something at the end of a block.

 Code like this:

 with closing(<module>.open(<arguments>)) as f:
 <block>

 is equivalent to this:

 f = <module>.open(<arguments>)
 try:
 <block>
 finally:
 f.close()

 """
 def __init__(self, thing):
 self.thing = thing
 def __enter__(self):
 return self.thing
 def __exit__(self, *exc_info):
 self.thing.close()


class _RedirectStream(AbstractContextManager):

 _stream = None

 def __init__(self, new_target):
 self._new_target = new_target
 # We use a list of old targets to make this CM re-entrant
 self._old_targets = []

 def __enter__(self):
 self._old_targets.append(getattr(sys, self._stream))
 setattr(sys, self._stream, self._new_target)
 return self._new_target

 def __exit__(self, exctype, excinst, exctb):
 setattr(sys, self._stream, self._old_targets.pop())


class redirect_stdout(_RedirectStream):
 """Context manager for temporarily redirecting stdout to another file.

 # How to send help() to stderr
 with redirect_stdout(sys.stderr):
 help(dir)

 # How to write help() to a file
 with open('help.txt', 'w') as f:
 with redirect_stdout(f):
 help(pow)
 """

 _stream = "stdout"


class redirect_stderr(_RedirectStream):
 """Context manager for temporarily redirecting stderr to another file."""

 _stream = "stderr"


class suppress(AbstractContextManager):
 """Context manager to suppress specified exceptions

 After the exception is suppressed, execution proceeds with the next
 statement following the with statement.

 with suppress(FileNotFoundError):
 os.remove(somefile)
 # Execution still resumes here if the file was already removed
 """

 def __init__(self, *exceptions):
 self._exceptions = exceptions

 def __enter__(self):
 pass

 def __exit__(self, exctype, excinst, exctb):
 # Unlike isinstance and issubclass, CPython exception handling
 # currently only looks at the concrete type hierarchy (ignoring
 # the instance and subclass checking hooks). While Guido considers
 # that a bug rather than a feature, it's a fairly hard one to fix
 # due to various internal implementation details. suppress provides
 # the simpler issubclass based semantics, rather than trying to
 # exactly reproduce the limitations of the CPython interpreter.
 #
 # See http://bugs.python.org/issue12029 for more details
 return exctype is not None and issubclass(exctype, self._exceptions)


class _BaseExitStack:
 """A base class for ExitStack and AsyncExitStack."""

 @staticmethod
 def _create_exit_wrapper(cm, cm_exit):
 return MethodType(cm_exit, cm)

 @staticmethod
 def _create_cb_wrapper(callback, /, *args, **kwds):
 def _exit_wrapper(exc_type, exc, tb):
 callback(*args, **kwds)
 return _exit_wrapper

 def __init__(self):
 self._exit_callbacks = deque()

 def pop_all(self):
 """Preserve the context stack by transferring it to a new instance."""
 new_stack = type(self)()
 new_stack._exit_callbacks = self._exit_callbacks
 self._exit_callbacks = deque()
 return new_stack

 def push(self, exit):
 """Registers a callback with the standard __exit__ method signature.

 Can suppress exceptions the same way __exit__ method can.
 Also accepts any object with an __exit__ method (registering a call
 to the method instead of the object itself).
 """
 # We use an unbound method rather than a bound method to follow
 # the standard lookup behaviour for special methods.
 _cb_type = type(exit)

 try:
 exit_method = _cb_type.__exit__
 except AttributeError:
 # Not a context manager, so assume it's a callable.
 self._push_exit_callback(exit)
 else:
 self._push_cm_exit(exit, exit_method)
 return exit # Allow use as a decorator.

 def enter_context(self, cm):
 """Enters the supplied context manager.

 If successful, also pushes its __exit__ method as a callback and
 returns the result of the __enter__ method.
 """
 # We look up the special methods on the type to match the with
 # statement.
 _cm_type = type(cm)
 _exit = _cm_type.__exit__
 result = _cm_type.__enter__(cm)
 self._push_cm_exit(cm, _exit)
 return result

 def callback(*args, **kwds):
 """Registers an arbitrary callback and arguments.

 Cannot suppress exceptions.
 """
 if len(args) >= 2:
 self, callback, *args = args
 elif not args:
 raise TypeError("descriptor 'callback' of '_BaseExitStack' object "
 "needs an argument")
 elif 'callback' in kwds:
 callback = kwds.pop('callback')
 self, *args = args
 import warnings
 warnings.warn("Passing 'callback' as keyword argument is deprecated",
 DeprecationWarning, stacklevel=2)
 else:
 raise TypeError('callback expected at least 1 positional argument, '
 'got %d' % (len(args)-1))

 _exit_wrapper = self._create_cb_wrapper(callback, *args, **kwds)

 # We changed the signature, so using @wraps is not appropriate, but
 # setting __wrapped__ may still help with introspection.
 _exit_wrapper.__wrapped__ = callback
 self._push_exit_callback(_exit_wrapper)
 return callback # Allow use as a decorator
 callback.__text_signature__ = '($self, callback, /, *args, **kwds)'

 def _push_cm_exit(self, cm, cm_exit):
 """Helper to correctly register callbacks to __exit__ methods."""
 _exit_wrapper = self._create_exit_wrapper(cm, cm_exit)
 self._push_exit_callback(_exit_wrapper, True)

 def _push_exit_callback(self, callback, is_sync=True):
 self._exit_callbacks.append((is_sync, callback))


# Inspired by discussions on http://bugs.python.org/issue13585
class ExitStack(_BaseExitStack, AbstractContextManager):
 """Context manager for dynamic management of a stack of exit callbacks.

 For example:
 with ExitStack() as stack:
 files = [stack.enter_context(open(fname)) for fname in filenames]
 # All opened files will automatically be closed at the end of
 # the with statement, even if attempts to open files later
 # in the list raise an exception.
 """

 def __enter__(self):
 return self

 def __exit__(self, *exc_details):
 received_exc = exc_details[0] is not None

 # We manipulate the exception state so it behaves as though
 # we were actually nesting multiple with statements
 frame_exc = sys.exc_info()[1]
 def _fix_exception_context(new_exc, old_exc):
 # Context may not be correct, so find the end of the chain
 while 1:
 exc_context = new_exc.__context__
 if exc_context is old_exc:
 # Context is already set correctly (see issue 20317)
 return
 if exc_context is None or exc_context is frame_exc:
 break
 new_exc = exc_context
 # Change the end of the chain to point to the exception
 # we expect it to reference
 new_exc.__context__ = old_exc

 # Callbacks are invoked in LIFO order to match the behaviour of
 # nested context managers
 suppressed_exc = False
 pending_raise = False
 while self._exit_callbacks:
 is_sync, cb = self._exit_callbacks.pop()
 assert is_sync
 try:
 if cb(*exc_details):
 suppressed_exc = True
 pending_raise = False
 exc_details = (None, None, None)
 except:
 new_exc_details = sys.exc_info()
 # simulate the stack of exceptions by setting the context
 _fix_exception_context(new_exc_details[1], exc_details[1])
 pending_raise = True
 exc_details = new_exc_details
 if pending_raise:
 try:
 # bare "raise exc_details[1]" replaces our carefully
 # set-up context
 fixed_ctx = exc_details[1].__context__
 raise exc_details[1]
 except BaseException:
 exc_details[1].__context__ = fixed_ctx
 raise
 return received_exc and suppressed_exc

 def close(self):
 """Immediately unwind the context stack."""
 self.__exit__(None, None, None)


# Inspired by discussions on https://bugs.python.org/issue29302
class AsyncExitStack(_BaseExitStack, AbstractAsyncContextManager):
 """Async context manager for dynamic management of a stack of exit
 callbacks.

 For example:
 async with AsyncExitStack() as stack:
 connections = [await stack.enter_async_context(get_connection())
 for i in range(5)]
 # All opened connections will automatically be released at the
 # end of the async with statement, even if attempts to open a
 # connection later in the list raise an exception.
 """

 @staticmethod
 def _create_async_exit_wrapper(cm, cm_exit):
 return MethodType(cm_exit, cm)

 @staticmethod
 def _create_async_cb_wrapper(callback, /, *args, **kwds):
 async def _exit_wrapper(exc_type, exc, tb):
 await callback(*args, **kwds)
 return _exit_wrapper

 async def enter_async_context(self, cm):
 """Enters the supplied async context manager.

 If successful, also pushes its __aexit__ method as a callback and
 returns the result of the __aenter__ method.
 """
 _cm_type = type(cm)
 _exit = _cm_type.__aexit__
 result = await _cm_type.__aenter__(cm)
 self._push_async_cm_exit(cm, _exit)
 return result

 def push_async_exit(self, exit):
 """Registers a coroutine function with the standard __aexit__ method
 signature.

 Can suppress exceptions the same way __aexit__ method can.
 Also accepts any object with an __aexit__ method (registering a call
 to the method instead of the object itself).
 """
 _cb_type = type(exit)
 try:
 exit_method = _cb_type.__aexit__
 except AttributeError:
 # Not an async context manager, so assume it's a coroutine function
 self._push_exit_callback(exit, False)
 else:
 self._push_async_cm_exit(exit, exit_method)
 return exit # Allow use as a decorator

 def push_async_callback(*args, **kwds):
 """Registers an arbitrary coroutine function and arguments.

 Cannot suppress exceptions.
 """
 if len(args) >= 2:
 self, callback, *args = args
 elif not args:
 raise TypeError("descriptor 'push_async_callback' of "
 "'AsyncExitStack' object needs an argument")
 elif 'callback' in kwds:
 callback = kwds.pop('callback')
 self, *args = args
 import warnings
 warnings.warn("Passing 'callback' as keyword argument is deprecated",
 DeprecationWarning, stacklevel=2)
 else:
 raise TypeError('push_async_callback expected at least 1 '
 'positional argument, got %d' % (len(args)-1))

 _exit_wrapper = self._create_async_cb_wrapper(callback, *args, **kwds)

 # We changed the signature, so using @wraps is not appropriate, but
 # setting __wrapped__ may still help with introspection.
 _exit_wrapper.__wrapped__ = callback
 self._push_exit_callback(_exit_wrapper, False)
 return callback # Allow use as a decorator
 push_async_callback.__text_signature__ = '($self, callback, /, *args, **kwds)'

 async def aclose(self):
 """Immediately unwind the context stack."""
 await self.__aexit__(None, None, None)

 def _push_async_cm_exit(self, cm, cm_exit):
 """Helper to correctly register coroutine function to __aexit__
 method."""
 _exit_wrapper = self._create_async_exit_wrapper(cm, cm_exit)
 self._push_exit_callback(_exit_wrapper, False)

 async def __aenter__(self):
 return self

 async def __aexit__(self, *exc_details):
 received_exc = exc_details[0] is not None

 # We manipulate the exception state so it behaves as though
 # we were actually nesting multiple with statements
 frame_exc = sys.exc_info()[1]
 def _fix_exception_context(new_exc, old_exc):
 # Context may not be correct, so find the end of the chain
 while 1:
 exc_context = new_exc.__context__
 if exc_context is old_exc:
 # Context is already set correctly (see issue 20317)
 return
 if exc_context is None or exc_context is frame_exc:
 break
 new_exc = exc_context
 # Change the end of the chain to point to the exception
 # we expect it to reference
 new_exc.__context__ = old_exc

 # Callbacks are invoked in LIFO order to match the behaviour of
 # nested context managers
 suppressed_exc = False
 pending_raise = False
 while self._exit_callbacks:
 is_sync, cb = self._exit_callbacks.pop()
 try:
 if is_sync:
 cb_suppress = cb(*exc_details)
 else:
 cb_suppress = await cb(*exc_details)

 if cb_suppress:
 suppressed_exc = True
 pending_raise = False
 exc_details = (None, None, None)
 except:
 new_exc_details = sys.exc_info()
 # simulate the stack of exceptions by setting the context
 _fix_exception_context(new_exc_details[1], exc_details[1])
 pending_raise = True
 exc_details = new_exc_details
 if pending_raise:
 try:
 # bare "raise exc_details[1]" replaces our carefully
 # set-up context
 fixed_ctx = exc_details[1].__context__
 raise exc_details[1]
 except BaseException:
 exc_details[1].__context__ = fixed_ctx
 raise
 return received_exc and suppressed_exc


class nullcontext(AbstractContextManager):
 """Context manager that does no additional processing.

 Used as a stand-in for a normal context manager, when a particular
 block of code is only sometimes used with a normal context manager:

 cm = optional_cm if condition else nullcontext()
 with cm:
 # Perform operation, using optional_cm if condition is True
 """

 def __init__(self, enter_result=None):
 self.enter_result = enter_result

 def __enter__(self):
 return self.enter_result

 def __exit__(self, *excinfo):
 pass