# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.

"""
Testing helpers related to the module system.
"""

from __future__ import division, absolute_import

__all__ = ['NoReactor', 'AlternateReactor']

import sys

import twisted.internet
from twisted.test.test_twisted import SetAsideModule



class NoReactor(SetAsideModule):
"""
Context manager that uninstalls the reactor, if any, and then restores it
afterwards.
"""

def __init__(self):
SetAsideModule.__init__(self, "twisted.internet.reactor")


def __enter__(self):
SetAsideModule.__enter__(self)
if "twisted.internet.reactor" in self.modules:
del twisted.internet.reactor


def __exit__(self, excType, excValue, traceback):
SetAsideModule.__exit__(self, excType, excValue, traceback)
# Clean up 'reactor' attribute that may have been set on
# twisted.internet:
reactor = self.modules.get("twisted.internet.reactor", None)
if reactor is not None:
twisted.internet.reactor = reactor
else:
try:
del twisted.internet.reactor
except AttributeError:
pass



class AlternateReactor(NoReactor):
"""
A context manager which temporarily installs a different object as the
global reactor.
"""

def __init__(self, reactor):
"""
@param reactor: Any object to install as the global reactor.
"""
NoReactor.__init__(self)
self.alternate = reactor


def __enter__(self):
NoReactor.__enter__(self)
twisted.internet.reactor = self.alternate
sys.modules['twisted.internet.reactor'] = self.alternate