import contextlib

import pytest

import pandas as pd
import pandas.util.testing as tm


@contextlib.contextmanager
def ensure_removed(obj, attr):
    """Ensure that an attribute added to 'obj' during the test is
    removed when we're done"""
    try:
        yield
    finally:
        try:
            delattr(obj, attr)
        except AttributeError:
            pass
        obj._accessors.discard(attr)


class MyAccessor(object):

    def __init__(self, obj):
        self.obj = obj
        self.item = 'item'

    @property
    def prop(self):
        return self.item

    def method(self):
        return self.item


@pytest.mark.parametrize('obj, registrar', [
    (pd.Series, pd.api.extensions.register_series_accessor),
    (pd.DataFrame, pd.api.extensions.register_dataframe_accessor),
    (pd.Index, pd.api.extensions.register_index_accessor)
])
def test_register(obj, registrar):
    with ensure_removed(obj, 'mine'):
        before = set(dir(obj))
        registrar('mine')(MyAccessor)
        assert obj([]).mine.prop == 'item'
        after = set(dir(obj))
        assert (before ^ after) == {'mine'}
        assert 'mine' in obj._accessors


def test_accessor_works():
    with ensure_removed(pd.Series, 'mine'):
        pd.api.extensions.register_series_accessor('mine')(MyAccessor)

        s = pd.Series([1, 2])
        assert s.mine.obj is s

        assert s.mine.prop == 'item'
        assert s.mine.method() == 'item'


def test_overwrite_warns():
    # Need to restore mean
    mean = pd.Series.mean
    try:
        with tm.assert_produces_warning(UserWarning) as w:
            pd.api.extensions.register_series_accessor('mean')(MyAccessor)
            s = pd.Series([1, 2])
            assert s.mean.prop == 'item'
        msg = str(w[0].message)
        assert 'mean' in msg
        assert 'MyAccessor' in msg
        assert 'Series' in msg
    finally:
        pd.Series.mean = mean


def test_raises_attribute_error():

    with ensure_removed(pd.Series, 'bad'):

        @pd.api.extensions.register_series_accessor("bad")
        class Bad(object):
            def __init__(self, data):
                raise AttributeError("whoops")

        with pytest.raises(AttributeError, match="whoops"):
            pd.Series([]).bad