# -*- test-case-name: twisted.test.test_monkey -*-

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

from __future__ import division, absolute_import


class MonkeyPatcher(object):
"""
Cover up attributes with new objects. Neat for monkey-patching things for
unit-testing purposes.
"""

def __init__(self, *patches):
# List of patches to apply in (obj, name, value).
self._patchesToApply = []
# List of the original values for things that have been patched.
# (obj, name, value) format.
self._originals = []
for patch in patches:
self.addPatch(*patch)


def addPatch(self, obj, name, value):
"""
Add a patch so that the attribute C{name} on C{obj} will be assigned to
C{value} when C{patch} is called or during C{runWithPatches}.

You can restore the original values with a call to restore().
"""
self._patchesToApply.append((obj, name, value))


def _alreadyPatched(self, obj, name):
"""
Has the C{name} attribute of C{obj} already been patched by this
patcher?
"""
for o, n, v in self._originals:
if (o, n) == (obj, name):
return True
return False


def patch(self):
"""
Apply all of the patches that have been specified with L{addPatch}.
Reverse this operation using L{restore}.
"""
for obj, name, value in self._patchesToApply:
if not self._alreadyPatched(obj, name):
self._originals.append((obj, name, getattr(obj, name)))
setattr(obj, name, value)


def restore(self):
"""
Restore all original values to any patched objects.
"""
while self._originals:
obj, name, value = self._originals.pop()
setattr(obj, name, value)


def runWithPatches(self, f, *args, **kw):
"""
Apply each patch already specified. Then run the function f with the
given args and kwargs. Restore everything when done.
"""
self.patch()
try:
return f(*args, **kw)
finally:
self.restore()