from datetime import datetime

import numpy as np
import pytest
from pytz import UTC

from pandas._libs.tslib import iNaT
from pandas._libs.tslibs import conversion, timezones, tzconversion

from pandas import Timestamp, date_range
import pandas._testing as tm


def _compare_utc_to_local(tz_didx):
    def f(x):
        return conversion.tz_convert_single(x, UTC, tz_didx.tz)

    result = tzconversion.tz_convert(tz_didx.asi8, UTC, tz_didx.tz)
    expected = np.vectorize(f)(tz_didx.asi8)

    tm.assert_numpy_array_equal(result, expected)


def _compare_local_to_utc(tz_didx, utc_didx):
    def f(x):
        return conversion.tz_convert_single(x, tz_didx.tz, UTC)

    result = tzconversion.tz_convert(utc_didx.asi8, tz_didx.tz, UTC)
    expected = np.vectorize(f)(utc_didx.asi8)

    tm.assert_numpy_array_equal(result, expected)


def test_tz_convert_single_matches_tz_convert_hourly(tz_aware_fixture):
    tz = tz_aware_fixture
    tz_didx = date_range("2014-03-01", "2015-01-10", freq="H", tz=tz)
    utc_didx = date_range("2014-03-01", "2015-01-10", freq="H")

    _compare_utc_to_local(tz_didx)
    _compare_local_to_utc(tz_didx, utc_didx)


@pytest.mark.parametrize("freq", ["D", "A"])
def test_tz_convert_single_matches_tz_convert(tz_aware_fixture, freq):
    tz = tz_aware_fixture
    tz_didx = date_range("2000-01-01", "2020-01-01", freq=freq, tz=tz)
    utc_didx = date_range("2000-01-01", "2020-01-01", freq=freq)

    _compare_utc_to_local(tz_didx)
    _compare_local_to_utc(tz_didx, utc_didx)


@pytest.mark.parametrize(
    "arr",
    [
        pytest.param(np.array([], dtype=np.int64), id="empty"),
        pytest.param(np.array([iNaT], dtype=np.int64), id="all_nat"),
    ],
)
def test_tz_convert_corner(arr):
    result = tzconversion.tz_convert(
        arr, timezones.maybe_get_tz("US/Eastern"), timezones.maybe_get_tz("Asia/Tokyo")
    )
    tm.assert_numpy_array_equal(result, arr)


@pytest.mark.parametrize("copy", [True, False])
@pytest.mark.parametrize("dtype", ["M8[ns]", "M8[s]"])
def test_length_zero_copy(dtype, copy):
    arr = np.array([], dtype=dtype)
    result = conversion.ensure_datetime64ns(arr, copy=copy)
    assert result.base is (None if copy else arr)


class SubDatetime(datetime):
    pass


@pytest.mark.parametrize(
    "dt, expected",
    [
        pytest.param(
            Timestamp("2000-01-01"), Timestamp("2000-01-01", tz=UTC), id="timestamp"
        ),
        pytest.param(
            datetime(2000, 1, 1), datetime(2000, 1, 1, tzinfo=UTC), id="datetime"
        ),
        pytest.param(
            SubDatetime(2000, 1, 1),
            SubDatetime(2000, 1, 1, tzinfo=UTC),
            id="subclassed_datetime",
        ),
    ],
)
def test_localize_pydatetime_dt_types(dt, expected):
    # GH 25851
    # ensure that subclassed datetime works with
    # localize_pydatetime
    result = conversion.localize_pydatetime(dt, UTC)
    assert result == expected
