import sys
# Block C implementation
sys.modules['_functools'] = None

import collections.abc
import functools
import unittest


class TestSingleDispatch(unittest.TestCase):

    def test_mro_conflicts(self):
        c = collections.abc
        @functools.singledispatch
        def g(arg):
            return "base"
        class O(c.Sized):
            def __len__(self):
                return 0
        o = O()
        self.assertEqual(g(o), "base")
        g.register(c.Iterable, lambda arg: "iterable")
        g.register(c.Container, lambda arg: "container")
        g.register(c.Sized, lambda arg: "sized")
        g.register(c.Set, lambda arg: "set")
        self.assertEqual(g(o), "sized")
        c.Iterable.register(O)
        self.assertEqual(g(o), "sized")   # because it's explicitly in __mro__
        c.Container.register(O)
        self.assertEqual(g(o), "sized")   # see above: Sized is in __mro__
        c.Set.register(O)
        self.assertEqual(g(o), "set")     # because c.Set is a subclass of
                                          # c.Sized and c.Container
        class P:
            pass
        p = P()
        self.assertEqual(g(p), "base")
        c.Iterable.register(P)
        self.assertEqual(g(p), "iterable")
        c.Container.register(P)
        with self.assertRaises(RuntimeError) as re_one:
            g(p)
        self.assertIn(
            str(re_one.exception),
            (("Ambiguous dispatch: <class 'collections.abc.Container'> "
              "or <class 'collections.abc.Iterable'>"),
             ("Ambiguous dispatch: <class 'collections.abc.Iterable'> "
              "or <class 'collections.abc.Container'>")),
        )
        class Q(c.Sized):
            def __len__(self):
                return 0
        q = Q()
        self.assertEqual(g(q), "sized")
        c.Iterable.register(Q)
        self.assertEqual(g(q), "sized")   # because it's explicitly in __mro__
        c.Set.register(Q)
        self.assertEqual(g(q), "set")     # because c.Set is a subclass of
                                          # c.Sized and c.Iterable
        @functools.singledispatch
        def h(arg):
            return "base"
        @h.register(c.Sized)
        def _(arg):
            return "sized"
        @h.register(c.Container)
        def _(arg):
            return "container"
        # Even though Sized and Container are explicit bases of MutableMapping,
        # this ABC is implicitly registered on defaultdict which makes all of
        # MutableMapping's bases implicit as well from defaultdict's
        # perspective.
        with self.assertRaises(RuntimeError) as re_two:
            h(collections.defaultdict(lambda: 0))
        self.assertIn(
            str(re_two.exception),
            (("Ambiguous dispatch: <class 'collections.abc.Container'> "
              "or <class 'collections.abc.Sized'>"),
             ("Ambiguous dispatch: <class 'collections.abc.Sized'> "
              "or <class 'collections.abc.Container'>")),
        )
        class R(collections.defaultdict):
            pass
        c.MutableSequence.register(R)
        @functools.singledispatch
        def i(arg):
            return "base"
        @i.register(c.MutableMapping)
        def _(arg):
            return "mapping"
        @i.register(c.MutableSequence)
        def _(arg):
            return "sequence"
        r = R()
        self.assertEqual(i(r), "sequence")
        class S:
            pass
        class T(S, c.Sized):
            def __len__(self):
                return 0
        t = T()
        self.assertEqual(h(t), "sized")
        c.Container.register(T)