"""
Class for wrapping sys.modules to detect http://bugs.python.org/issue14847
"""
from __future__ import print_function, unicode_literals

import sys
import functools
import traceback
import inspect


class DelWrapper(object):
    """
    Object to delegate for sys.modules, but print the stack when a del
    operation occurs on specific keys.
    """

    def __init__(self):
        self.orig = sys.modules
        sys.modules = self

    def __delitem__(self, item):
        if item.startswith('encodings.'):
            msg = "*** deletion of {item} detected ***".format(**vars())
            print(msg, file=sys.stderr)
            frame = inspect.currentframe().f_back
            traceback.print_stack(frame)
            print("*" * len(msg))
            # suppress the deletion
            return
        del self.orig[item]

    def __getattr__(self, attr):
        return getattr(self.orig, attr)

    # need to delegate all of the private methods, as __getattr__ will not
    def __iter__(self):
        return iter(self.orig)

    def __getitem__(self, item):
        return self.orig[item]

    def __setitem__(self, item, value):
        self.orig[item] = value

    def __len__(self):
        return len(self.orig)

    # create a context manager
    def __enter__(self):
        return self

    def __exit__(self, type, val, tb):
        sys.modules = self.orig

    @classmethod
    def decorate(cls, func):
        @functools.wraps(func)
        def wrapper(*args, **kwargs):
            with cls():
                return func(*args, **kwargs)
        return wrapper


@DelWrapper.decorate
def test_protect_failure():
    """
    Using DelWrapper should prevent .decode from causing errors.
    """
    b'x'.decode('utf-8')
    del __import__('locale').encodings
    del sys.modules['encodings.utf_8'], sys.modules['encodings']
    b'x'.decode('utf-8')


@DelWrapper.decorate
def test_iterable():
    """
    sys.modules needs to be iterable
    """
    iter(sys.modules)


@DelWrapper.decorate
def test_dunder_import():
    __import__('collections')
    assert 'collections' in sys.modules


@DelWrapper.decorate
def test_private_methods():
    __import__('abc')
    sys.modules.__getitem__('abc')
    sys.modules['abc']
    sys.modules['foo'] = None
    assert 'foo' in sys.modules
    assert 'foo' in sys.modules.orig
    del sys.modules['foo']
    assert 'foo' not in sys.modules
    assert 'foo' not in sys.modules.orig
    assert len(sys.modules) == len(sys.modules.orig)

if __name__ == '__main__':
    test_protect_failure()
    test_iterable()
    test_dunder_import()
    test_private_methods()