# (C) Copyright 2005-2020 Enthought, Inc., Austin, TX
# All rights reserved.
#
# This software is provided without warranty under the terms of the BSD
# license included in LICENSE.txt and may be redistributed only under
# the conditions described in the aforementioned license. The license
# is also available online at http://www.enthought.com/licenses/BSD.txt
#
# Thanks for using Enthought open source!

""" Test whether HasTraits objects with cycles can be garbage collected.
"""

import gc
import time
import unittest

# Enthought library imports
from traits.api import HasTraits, Any, DelegatesTo, Instance, Int


class TestCase(unittest.TestCase):
    def _simple_cycle_helper(self, foo_class):
        """ Can the garbage collector clean up a cycle with traits objects?
        """

        # Create two Foo objects that refer to each other.
        first = foo_class()
        second = foo_class(child=first)
        first.child = second

        # get their ids
        foo_ids = [id(first), id(second)]

        # delete the items so that they can be garbage collected
        del first, second

        # tell the garbage collector to pick up the litter.
        gc.collect()

        # Now grab all objects in the process and ask for their ids
        all_ids = [id(obj) for obj in gc.get_objects()]

        # Ensure that neither of the Foo object ids are in this list
        for foo_id in foo_ids:
            self.assertTrue(foo_id not in all_ids)

    def test_simple_cycle_oldstyle_class(self):
        """ Can the garbage collector clean up a cycle with old style class?
        """

        class Foo:
            def __init__(self, child=None):
                self.child = child

        self._simple_cycle_helper(Foo)

    def test_simple_cycle_newstyle_class(self):
        """ Can the garbage collector clean up a cycle with new style class?
        """

        class Foo(object):
            def __init__(self, child=None):
                self.child = child

        self._simple_cycle_helper(Foo)

    def test_simple_cycle_hastraits(self):
        """ Can the garbage collector clean up a cycle with traits objects?
        """

        class Foo(HasTraits):
            child = Any

        self._simple_cycle_helper(Foo)

    def test_reference_to_trait_dict(self):
        """ Does a HasTraits object refer to its __dict__ object?

            This test may point to why the previous one fails.  Even if it
            doesn't, the functionality is needed for detecting problems
            with memory in debug.memory_tracker
        """

        class Foo(HasTraits):
            child = Any

        foo = Foo()

        # It seems like foo sometimes has not finished construction yet, so
        # the frame found by referrers is not _exactly_ the same as Foo(). For
        # more information, see the gc doc: http://docs.python.org/lib/module-
        # gc.html
        #
        # The documentation says that this (get_referrers) should be used for
        # no purpose other than debugging, so this is really not a good way to
        # test the code.

        time.sleep(0.1)
        referrers = gc.get_referrers(foo.__dict__)

        self.assertTrue(len(referrers) > 0)
        self.assertTrue(foo in referrers)

    def test_delegates_to(self):
        """ Tests if an object that delegates to another is freed.
        """

        class Base(HasTraits):
            """ Object we are delegating to. """

            i = Int

        class Delegates(HasTraits):
            """ Object that delegates. """

            b = Instance(Base)

            i = DelegatesTo("b")

        # Make a pair of object
        b = Base()
        d = Delegates(b=b)

        # Delete d and thoroughly collect garbage
        del d
        for i in range(3):
            gc.collect(2)

        # See if we still have a Delegates
        ds = [obj for obj in gc.get_objects() if isinstance(obj, Delegates)]
        self.assertEqual(ds, [])
