from __future__ import annotations

import datetime as dt
import warnings

import numpy as np
import pandas as pd
import pytest
from numpy import array, nan

from xarray import DataArray, Dataset, cftime_range, concat
from xarray.core import dtypes, duck_array_ops
from xarray.core.duck_array_ops import (
    array_notnull_equiv,
    concatenate,
    count,
    first,
    gradient,
    last,
    least_squares,
    mean,
    np_timedelta64_to_float,
    pd_timedelta_to_float,
    push,
    py_timedelta_to_float,
    stack,
    timedelta_to_numeric,
    where,
)
from xarray.core.pycompat import array_type
from xarray.testing import assert_allclose, assert_equal, assert_identical
from xarray.tests import (
    arm_xfail,
    assert_array_equal,
    has_dask,
    has_scipy,
    raise_if_dask_computes,
    requires_bottleneck,
    requires_cftime,
    requires_dask,
)

dask_array_type = array_type("dask")


class TestOps:
    @pytest.fixture(autouse=True)
    def setUp(self):
        self.x = array(
            [
                [
                    [nan, nan, 2.0, nan],
                    [nan, 5.0, 6.0, nan],
                    [8.0, 9.0, 10.0, nan],
                ],
                [
                    [nan, 13.0, 14.0, 15.0],
                    [nan, 17.0, 18.0, nan],
                    [nan, 21.0, nan, nan],
                ],
            ]
        )

    def test_first(self):
        expected_results = [
            array([[nan, 13, 2, 15], [nan, 5, 6, nan], [8, 9, 10, nan]]),
            array([[8, 5, 2, nan], [nan, 13, 14, 15]]),
            array([[2, 5, 8], [13, 17, 21]]),
        ]
        for axis, expected in zip([0, 1, 2, -3, -2, -1], 2 * expected_results):
            actual = first(self.x, axis)
            assert_array_equal(expected, actual)

        expected = self.x[0]
        actual = first(self.x, axis=0, skipna=False)
        assert_array_equal(expected, actual)

        expected = self.x[..., 0]
        actual = first(self.x, axis=-1, skipna=False)
        assert_array_equal(expected, actual)

        with pytest.raises(IndexError, match=r"out of bounds"):
            first(self.x, 3)

    def test_last(self):
        expected_results = [
            array([[nan, 13, 14, 15], [nan, 17, 18, nan], [8, 21, 10, nan]]),
            array([[8, 9, 10, nan], [nan, 21, 18, 15]]),
            array([[2, 6, 10], [15, 18, 21]]),
        ]
        for axis, expected in zip([0, 1, 2, -3, -2, -1], 2 * expected_results):
            actual = last(self.x, axis)
            assert_array_equal(expected, actual)

        expected = self.x[-1]
        actual = last(self.x, axis=0, skipna=False)
        assert_array_equal(expected, actual)

        expected = self.x[..., -1]
        actual = last(self.x, axis=-1, skipna=False)
        assert_array_equal(expected, actual)

        with pytest.raises(IndexError, match=r"out of bounds"):
            last(self.x, 3)

    def test_count(self):
        assert 12 == count(self.x)

        expected = array([[1, 2, 3], [3, 2, 1]])
        assert_array_equal(expected, count(self.x, axis=-1))

        assert 1 == count(np.datetime64("2000-01-01"))

    def test_where_type_promotion(self):
        result = where([True, False], [1, 2], ["a", "b"])
        assert_array_equal(result, np.array([1, "b"], dtype=object))

        result = where([True, False], np.array([1, 2], np.float32), np.nan)
        assert result.dtype == np.float32
        assert_array_equal(result, np.array([1, np.nan], dtype=np.float32))

    def test_stack_type_promotion(self):
        result = stack([1, "b"])
        assert_array_equal(result, np.array([1, "b"], dtype=object))

    def test_concatenate_type_promotion(self):
        result = concatenate([[1], ["b"]])
        assert_array_equal(result, np.array([1, "b"], dtype=object))

    @pytest.mark.filterwarnings("error")
    def test_all_nan_arrays(self):
        assert np.isnan(mean([np.nan, np.nan]))


@requires_dask
class TestDaskOps(TestOps):
    @pytest.fixture(autouse=True)
    def setUp(self):
        import dask.array

        self.x = dask.array.from_array(
            [
                [
                    [nan, nan, 2.0, nan],
                    [nan, 5.0, 6.0, nan],
                    [8.0, 9.0, 10.0, nan],
                ],
                [
                    [nan, 13.0, 14.0, 15.0],
                    [nan, 17.0, 18.0, nan],
                    [nan, 21.0, nan, nan],
                ],
            ],
            chunks=(2, 1, 2),
        )


def test_cumsum_1d():
    inputs = np.array([0, 1, 2, 3])
    expected = np.array([0, 1, 3, 6])
    actual = duck_array_ops.cumsum(inputs)
    assert_array_equal(expected, actual)

    actual = duck_array_ops.cumsum(inputs, axis=0)
    assert_array_equal(expected, actual)

    actual = duck_array_ops.cumsum(inputs, axis=-1)
    assert_array_equal(expected, actual)

    actual = duck_array_ops.cumsum(inputs, axis=(0,))
    assert_array_equal(expected, actual)

    actual = duck_array_ops.cumsum(inputs, axis=())
    assert_array_equal(inputs, actual)


def test_cumsum_2d():
    inputs = np.array([[1, 2], [3, 4]])

    expected = np.array([[1, 3], [4, 10]])
    actual = duck_array_ops.cumsum(inputs)
    assert_array_equal(expected, actual)

    actual = duck_array_ops.cumsum(inputs, axis=(0, 1))
    assert_array_equal(expected, actual)

    actual = duck_array_ops.cumsum(inputs, axis=())
    assert_array_equal(inputs, actual)


def test_cumprod_2d():
    inputs = np.array([[1, 2], [3, 4]])

    expected = np.array([[1, 2], [3, 2 * 3 * 4]])
    actual = duck_array_ops.cumprod(inputs)
    assert_array_equal(expected, actual)

    actual = duck_array_ops.cumprod(inputs, axis=(0, 1))
    assert_array_equal(expected, actual)

    actual = duck_array_ops.cumprod(inputs, axis=())
    assert_array_equal(inputs, actual)


class TestArrayNotNullEquiv:
    @pytest.mark.parametrize(
        "arr1, arr2",
        [
            (np.array([1, 2, 3]), np.array([1, 2, 3])),
            (np.array([1, 2, np.nan]), np.array([1, np.nan, 3])),
            (np.array([np.nan, 2, np.nan]), np.array([1, np.nan, np.nan])),
        ],
    )
    def test_equal(self, arr1, arr2):
        assert array_notnull_equiv(arr1, arr2)

    def test_some_not_equal(self):
        a = np.array([1, 2, 4])
        b = np.array([1, np.nan, 3])
        assert not array_notnull_equiv(a, b)

    def test_wrong_shape(self):
        a = np.array([[1, np.nan, np.nan, 4]])
        b = np.array([[1, 2], [np.nan, 4]])
        assert not array_notnull_equiv(a, b)

    @pytest.mark.parametrize(
        "val1, val2, val3, null",
        [
            (
                np.datetime64("2000"),
                np.datetime64("2001"),
                np.datetime64("2002"),
                np.datetime64("NaT"),
            ),
            (1.0, 2.0, 3.0, np.nan),
            ("foo", "bar", "baz", None),
            ("foo", "bar", "baz", np.nan),
        ],
    )
    def test_types(self, val1, val2, val3, null):
        dtype = object if isinstance(val1, str) else None
        arr1 = np.array([val1, null, val3, null], dtype=dtype)
        arr2 = np.array([val1, val2, null, null], dtype=dtype)
        assert array_notnull_equiv(arr1, arr2)


def construct_dataarray(dim_num, dtype, contains_nan, dask):
    # dimnum <= 3
    rng = np.random.RandomState(0)
    shapes = [16, 8, 4][:dim_num]
    dims = ("x", "y", "z")[:dim_num]

    if np.issubdtype(dtype, np.floating):
        array = rng.randn(*shapes).astype(dtype)
    elif np.issubdtype(dtype, np.integer):
        array = rng.randint(0, 10, size=shapes).astype(dtype)
    elif np.issubdtype(dtype, np.bool_):
        array = rng.randint(0, 1, size=shapes).astype(dtype)
    elif dtype == str:
        array = rng.choice(["a", "b", "c", "d"], size=shapes)
    else:
        raise ValueError

    if contains_nan:
        inds = rng.choice(range(array.size), int(array.size * 0.2))
        dtype, fill_value = dtypes.maybe_promote(array.dtype)
        array = array.astype(dtype)
        array.flat[inds] = fill_value

    da = DataArray(array, dims=dims, coords={"x": np.arange(16)}, name="da")

    if dask and has_dask:
        chunks = {d: 4 for d in dims}
        da = da.chunk(chunks)

    return da


def from_series_or_scalar(se):
    if isinstance(se, pd.Series):
        return DataArray.from_series(se)
    else:  # scalar case
        return DataArray(se)


def series_reduce(da, func, dim, **kwargs):
    """convert DataArray to pd.Series, apply pd.func, then convert back to
    a DataArray. Multiple dims cannot be specified."""

    # pd no longer accepts skipna=None https://github.com/pandas-dev/pandas/issues/44178
    if kwargs.get("skipna", True) is None:
        kwargs["skipna"] = True

    if dim is None or da.ndim == 1:
        se = da.to_series()
        return from_series_or_scalar(getattr(se, func)(**kwargs))
    else:
        da1 = []
        dims = list(da.dims)
        dims.remove(dim)
        d = dims[0]
        for i in range(len(da[d])):
            da1.append(series_reduce(da.isel(**{d: i}), func, dim, **kwargs))

        if d in da.coords:
            return concat(da1, dim=da[d])
        return concat(da1, dim=d)


def assert_dask_array(da, dask):
    if dask and da.ndim > 0:
        assert isinstance(da.data, dask_array_type)


@arm_xfail
@pytest.mark.filterwarnings("ignore:All-NaN .* encountered:RuntimeWarning")
@pytest.mark.parametrize("dask", [False, True] if has_dask else [False])
def test_datetime_mean(dask: bool) -> None:
    # Note: only testing numpy, as dask is broken upstream
    da = DataArray(
        np.array(["2010-01-01", "NaT", "2010-01-03", "NaT", "NaT"], dtype="M8[ns]"),
        dims=["time"],
    )
    if dask:
        # Trigger use case where a chunk is full of NaT
        da = da.chunk({"time": 3})

    expect = DataArray(np.array("2010-01-02", dtype="M8[ns]"))
    expect_nat = DataArray(np.array("NaT", dtype="M8[ns]"))

    actual = da.mean()
    if dask:
        assert actual.chunks is not None
    assert_equal(actual, expect)

    actual = da.mean(skipna=False)
    if dask:
        assert actual.chunks is not None
    assert_equal(actual, expect_nat)

    # tests for 1d array full of NaT
    assert_equal(da[[1]].mean(), expect_nat)
    assert_equal(da[[1]].mean(skipna=False), expect_nat)

    # tests for a 0d array
    assert_equal(da[0].mean(), da[0])
    assert_equal(da[0].mean(skipna=False), da[0])
    assert_equal(da[1].mean(), expect_nat)
    assert_equal(da[1].mean(skipna=False), expect_nat)


@requires_cftime
@pytest.mark.parametrize("dask", [False, True])
def test_cftime_datetime_mean(dask):
    if dask and not has_dask:
        pytest.skip("requires dask")

    times = cftime_range("2000", periods=4)
    da = DataArray(times, dims=["time"])
    da_2d = DataArray(times.values.reshape(2, 2))

    if dask:
        da = da.chunk({"time": 2})
        da_2d = da_2d.chunk({"dim_0": 2})

    expected = da.isel(time=0)
    # one compute needed to check the array contains cftime datetimes
    with raise_if_dask_computes(max_computes=1):
        result = da.isel(time=0).mean()
    assert_dask_array(result, dask)
    assert_equal(result, expected)

    expected = DataArray(times.date_type(2000, 1, 2, 12))
    with raise_if_dask_computes(max_computes=1):
        result = da.mean()
    assert_dask_array(result, dask)
    assert_equal(result, expected)

    with raise_if_dask_computes(max_computes=1):
        result = da_2d.mean()
    assert_dask_array(result, dask)
    assert_equal(result, expected)


@requires_cftime
@requires_dask
def test_mean_over_non_time_dim_of_dataset_with_dask_backed_cftime_data():
    # Regression test for part two of GH issue 5897: averaging over a non-time
    # dimension still fails if the time variable is dask-backed.
    ds = Dataset(
        {
            "var1": (("time",), cftime_range("2021-10-31", periods=10, freq="D")),
            "var2": (("x",), list(range(10))),
        }
    )
    expected = ds.mean("x")
    result = ds.chunk({}).mean("x")
    assert_equal(result, expected)


@requires_cftime
def test_cftime_datetime_mean_long_time_period():
    import cftime

    times = np.array(
        [
            [
                cftime.DatetimeNoLeap(400, 12, 31, 0, 0, 0, 0),
                cftime.DatetimeNoLeap(520, 12, 31, 0, 0, 0, 0),
            ],
            [
                cftime.DatetimeNoLeap(520, 12, 31, 0, 0, 0, 0),
                cftime.DatetimeNoLeap(640, 12, 31, 0, 0, 0, 0),
            ],
            [
                cftime.DatetimeNoLeap(640, 12, 31, 0, 0, 0, 0),
                cftime.DatetimeNoLeap(760, 12, 31, 0, 0, 0, 0),
            ],
        ]
    )

    da = DataArray(times, dims=["time", "d2"])
    result = da.mean("d2")
    expected = DataArray(
        [
            cftime.DatetimeNoLeap(460, 12, 31, 0, 0, 0, 0),
            cftime.DatetimeNoLeap(580, 12, 31, 0, 0, 0, 0),
            cftime.DatetimeNoLeap(700, 12, 31, 0, 0, 0, 0),
        ],
        dims=["time"],
    )
    assert_equal(result, expected)


def test_empty_axis_dtype():
    ds = Dataset()
    ds["pos"] = [1, 2, 3]
    ds["data"] = ("pos", "time"), [[1.0, 2.0], [3.0, 4.0], [5.0, 6.0]]
    ds["var"] = "pos", [2, 3, 4]
    assert_identical(ds.mean(dim="time")["var"], ds["var"])
    assert_identical(ds.max(dim="time")["var"], ds["var"])
    assert_identical(ds.min(dim="time")["var"], ds["var"])
    assert_identical(ds.sum(dim="time")["var"], ds["var"])


@pytest.mark.parametrize("dim_num", [1, 2])
@pytest.mark.parametrize("dtype", [float, int, np.float32, np.bool_])
@pytest.mark.parametrize("dask", [False, True])
@pytest.mark.parametrize("func", ["sum", "min", "max", "mean", "var"])
# TODO test cumsum, cumprod
@pytest.mark.parametrize("skipna", [False, True])
@pytest.mark.parametrize("aggdim", [None, "x"])
def test_reduce(dim_num, dtype, dask, func, skipna, aggdim):
    if aggdim == "y" and dim_num < 2:
        pytest.skip("dim not in this test")

    if dtype == np.bool_ and func == "mean":
        pytest.skip("numpy does not support this")

    if dask and not has_dask:
        pytest.skip("requires dask")

    if dask and skipna is False and dtype in [np.bool_]:
        pytest.skip("dask does not compute object-typed array")

    rtol = 1e-04 if dtype == np.float32 else 1e-05

    da = construct_dataarray(dim_num, dtype, contains_nan=True, dask=dask)
    axis = None if aggdim is None else da.get_axis_num(aggdim)

    # TODO: remove these after resolving
    # https://github.com/dask/dask/issues/3245
    with warnings.catch_warnings():
        warnings.filterwarnings("ignore", "Mean of empty slice")
        warnings.filterwarnings("ignore", "All-NaN slice")
        warnings.filterwarnings("ignore", "invalid value encountered in")

        if da.dtype.kind == "O" and skipna:
            # Numpy < 1.13 does not handle object-type array.
            try:
                if skipna:
                    expected = getattr(np, f"nan{func}")(da.values, axis=axis)
                else:
                    expected = getattr(np, func)(da.values, axis=axis)

                actual = getattr(da, func)(skipna=skipna, dim=aggdim)
                assert_dask_array(actual, dask)
                np.testing.assert_allclose(
                    actual.values, np.array(expected), rtol=1.0e-4, equal_nan=True
                )
            except (TypeError, AttributeError, ZeroDivisionError):
                # TODO currently, numpy does not support some methods such as
                # nanmean for object dtype
                pass

        actual = getattr(da, func)(skipna=skipna, dim=aggdim)

        # for dask case, make sure the result is the same for numpy backend
        expected = getattr(da.compute(), func)(skipna=skipna, dim=aggdim)
        assert_allclose(actual, expected, rtol=rtol)

        # make sure the compatiblility with pandas' results.
        if func in ["var", "std"]:
            expected = series_reduce(da, func, skipna=skipna, dim=aggdim, ddof=0)
            assert_allclose(actual, expected, rtol=rtol)
            # also check ddof!=0 case
            actual = getattr(da, func)(skipna=skipna, dim=aggdim, ddof=5)
            if dask:
                assert isinstance(da.data, dask_array_type)
            expected = series_reduce(da, func, skipna=skipna, dim=aggdim, ddof=5)
            assert_allclose(actual, expected, rtol=rtol)
        else:
            expected = series_reduce(da, func, skipna=skipna, dim=aggdim)
            assert_allclose(actual, expected, rtol=rtol)

        # make sure the dtype argument
        if func not in ["max", "min"]:
            actual = getattr(da, func)(skipna=skipna, dim=aggdim, dtype=float)
            assert_dask_array(actual, dask)
            assert actual.dtype == float

        # without nan
        da = construct_dataarray(dim_num, dtype, contains_nan=False, dask=dask)
        actual = getattr(da, func)(skipna=skipna)
        if dask:
            assert isinstance(da.data, dask_array_type)
        expected = getattr(np, f"nan{func}")(da.values)
        if actual.dtype == object:
            assert actual.values == np.array(expected)
        else:
            assert np.allclose(actual.values, np.array(expected), rtol=rtol)


@pytest.mark.parametrize("dim_num", [1, 2])
@pytest.mark.parametrize("dtype", [float, int, np.float32, np.bool_, str])
@pytest.mark.parametrize("contains_nan", [True, False])
@pytest.mark.parametrize("dask", [False, True])
@pytest.mark.parametrize("func", ["min", "max"])
@pytest.mark.parametrize("skipna", [False, True])
@pytest.mark.parametrize("aggdim", ["x", "y"])
def test_argmin_max(dim_num, dtype, contains_nan, dask, func, skipna, aggdim):
    # pandas-dev/pandas#16830, we do not check consistency with pandas but
    # just make sure da[da.argmin()] == da.min()

    if aggdim == "y" and dim_num < 2:
        pytest.skip("dim not in this test")

    if dask and not has_dask:
        pytest.skip("requires dask")

    if contains_nan:
        if not skipna:
            pytest.skip("numpy's argmin (not nanargmin) does not handle object-dtype")
        if skipna and np.dtype(dtype).kind in "iufc":
            pytest.skip("numpy's nanargmin raises ValueError for all nan axis")
    da = construct_dataarray(dim_num, dtype, contains_nan=contains_nan, dask=dask)

    with warnings.catch_warnings():
        warnings.filterwarnings("ignore", "All-NaN slice")

        actual = da.isel(
            **{aggdim: getattr(da, "arg" + func)(dim=aggdim, skipna=skipna).compute()}
        )
        expected = getattr(da, func)(dim=aggdim, skipna=skipna)
        assert_allclose(
            actual.drop_vars(list(actual.coords)),
            expected.drop_vars(list(expected.coords)),
        )


def test_argmin_max_error():
    da = construct_dataarray(2, np.bool_, contains_nan=True, dask=False)
    da[0] = np.nan
    with pytest.raises(ValueError):
        da.argmin(dim="y")


@pytest.mark.parametrize(
    "array",
    [
        np.array([np.datetime64("2000-01-01"), np.datetime64("NaT")]),
        np.array([np.timedelta64(1, "h"), np.timedelta64("NaT")]),
        np.array([0.0, np.nan]),
        np.array([1j, np.nan]),
        np.array(["foo", np.nan], dtype=object),
    ],
)
def test_isnull(array):
    expected = np.array([False, True])
    actual = duck_array_ops.isnull(array)
    np.testing.assert_equal(expected, actual)


@requires_dask
def test_isnull_with_dask():
    da = construct_dataarray(2, np.float32, contains_nan=True, dask=True)
    assert isinstance(da.isnull().data, dask_array_type)
    assert_equal(da.isnull().load(), da.load().isnull())


@pytest.mark.skipif(not has_dask, reason="This is for dask.")
@pytest.mark.parametrize("axis", [0, -1, 1])
@pytest.mark.parametrize("edge_order", [1, 2])
def test_dask_gradient(axis, edge_order):
    import dask.array as da

    array = np.array(np.random.randn(100, 5, 40))
    x = np.exp(np.linspace(0, 1, array.shape[axis]))

    darray = da.from_array(array, chunks=[(6, 30, 30, 20, 14), 5, 8])
    expected = gradient(array, x, axis=axis, edge_order=edge_order)
    actual = gradient(darray, x, axis=axis, edge_order=edge_order)

    assert isinstance(actual, da.Array)
    assert_array_equal(actual, expected)


@pytest.mark.parametrize("dim_num", [1, 2])
@pytest.mark.parametrize("dtype", [float, int, np.float32, np.bool_])
@pytest.mark.parametrize("dask", [False, True])
@pytest.mark.parametrize("func", ["sum", "prod"])
@pytest.mark.parametrize("aggdim", [None, "x"])
@pytest.mark.parametrize("contains_nan", [True, False])
@pytest.mark.parametrize("skipna", [True, False, None])
def test_min_count(dim_num, dtype, dask, func, aggdim, contains_nan, skipna):
    if dask and not has_dask:
        pytest.skip("requires dask")

    da = construct_dataarray(dim_num, dtype, contains_nan=contains_nan, dask=dask)
    min_count = 3

    # If using Dask, the function call should be lazy.
    with raise_if_dask_computes():
        actual = getattr(da, func)(dim=aggdim, skipna=skipna, min_count=min_count)

    expected = series_reduce(da, func, skipna=skipna, dim=aggdim, min_count=min_count)
    assert_allclose(actual, expected)
    assert_dask_array(actual, dask)


@pytest.mark.parametrize("dtype", [float, int, np.float32, np.bool_])
@pytest.mark.parametrize("dask", [False, True])
@pytest.mark.parametrize("func", ["sum", "prod"])
def test_min_count_nd(dtype, dask, func):
    if dask and not has_dask:
        pytest.skip("requires dask")

    min_count = 3
    dim_num = 3
    da = construct_dataarray(dim_num, dtype, contains_nan=True, dask=dask)

    # If using Dask, the function call should be lazy.
    with raise_if_dask_computes():
        actual = getattr(da, func)(
            dim=["x", "y", "z"], skipna=True, min_count=min_count
        )

    # Supplying all dims is equivalent to supplying `...` or `None`
    expected = getattr(da, func)(dim=..., skipna=True, min_count=min_count)

    assert_allclose(actual, expected)
    assert_dask_array(actual, dask)


@pytest.mark.parametrize("dask", [False, True])
@pytest.mark.parametrize("func", ["sum", "prod"])
@pytest.mark.parametrize("dim", [None, "a", "b"])
def test_min_count_specific(dask, func, dim):
    if dask and not has_dask:
        pytest.skip("requires dask")

    # Simple array with four non-NaN values.
    da = DataArray(np.ones((6, 6), dtype=np.float64) * np.nan, dims=("a", "b"))
    da[0][0] = 2
    da[0][3] = 2
    da[3][0] = 2
    da[3][3] = 2
    if dask:
        da = da.chunk({"a": 3, "b": 3})

    # Expected result if we set min_count to the number of non-NaNs in a
    # row/column/the entire array.
    if dim:
        min_count = 2
        expected = DataArray(
            [4.0, np.nan, np.nan] * 2, dims=("a" if dim == "b" else "b",)
        )
    else:
        min_count = 4
        expected = DataArray(8.0 if func == "sum" else 16.0)

    # Check for that min_count.
    with raise_if_dask_computes():
        actual = getattr(da, func)(dim, skipna=True, min_count=min_count)
    assert_dask_array(actual, dask)
    assert_allclose(actual, expected)

    # With min_count being one higher, should get all NaN.
    min_count += 1
    expected *= np.nan
    with raise_if_dask_computes():
        actual = getattr(da, func)(dim, skipna=True, min_count=min_count)
    assert_dask_array(actual, dask)
    assert_allclose(actual, expected)


@pytest.mark.parametrize("func", ["sum", "prod"])
def test_min_count_dataset(func):
    da = construct_dataarray(2, dtype=float, contains_nan=True, dask=False)
    ds = Dataset({"var1": da}, coords={"scalar": 0})
    actual = getattr(ds, func)(dim="x", skipna=True, min_count=3)["var1"]
    expected = getattr(ds["var1"], func)(dim="x", skipna=True, min_count=3)
    assert_allclose(actual, expected)


@pytest.mark.parametrize("dtype", [float, int, np.float32, np.bool_])
@pytest.mark.parametrize("dask", [False, True])
@pytest.mark.parametrize("skipna", [False, True])
@pytest.mark.parametrize("func", ["sum", "prod"])
def test_multiple_dims(dtype, dask, skipna, func):
    if dask and not has_dask:
        pytest.skip("requires dask")
    da = construct_dataarray(3, dtype, contains_nan=True, dask=dask)

    actual = getattr(da, func)(("x", "y"), skipna=skipna)
    expected = getattr(getattr(da, func)("x", skipna=skipna), func)("y", skipna=skipna)
    assert_allclose(actual, expected)


@pytest.mark.parametrize("dask", [True, False])
def test_datetime_to_numeric_datetime64(dask):
    if dask and not has_dask:
        pytest.skip("requires dask")

    times = pd.date_range("2000", periods=5, freq="7D").values
    if dask:
        import dask.array

        times = dask.array.from_array(times, chunks=-1)

    with raise_if_dask_computes():
        result = duck_array_ops.datetime_to_numeric(times, datetime_unit="h")
    expected = 24 * np.arange(0, 35, 7)
    np.testing.assert_array_equal(result, expected)

    offset = times[1]
    with raise_if_dask_computes():
        result = duck_array_ops.datetime_to_numeric(
            times, offset=offset, datetime_unit="h"
        )
    expected = 24 * np.arange(-7, 28, 7)
    np.testing.assert_array_equal(result, expected)

    dtype = np.float32
    with raise_if_dask_computes():
        result = duck_array_ops.datetime_to_numeric(
            times, datetime_unit="h", dtype=dtype
        )
    expected = 24 * np.arange(0, 35, 7).astype(dtype)
    np.testing.assert_array_equal(result, expected)


@requires_cftime
@pytest.mark.parametrize("dask", [True, False])
def test_datetime_to_numeric_cftime(dask):
    if dask and not has_dask:
        pytest.skip("requires dask")

    times = cftime_range("2000", periods=5, freq="7D", calendar="standard").values
    if dask:
        import dask.array

        times = dask.array.from_array(times, chunks=-1)
    with raise_if_dask_computes():
        result = duck_array_ops.datetime_to_numeric(times, datetime_unit="h", dtype=int)
    expected = 24 * np.arange(0, 35, 7)
    np.testing.assert_array_equal(result, expected)

    offset = times[1]
    with raise_if_dask_computes():
        result = duck_array_ops.datetime_to_numeric(
            times, offset=offset, datetime_unit="h", dtype=int
        )
    expected = 24 * np.arange(-7, 28, 7)
    np.testing.assert_array_equal(result, expected)

    dtype = np.float32
    with raise_if_dask_computes():
        result = duck_array_ops.datetime_to_numeric(
            times, datetime_unit="h", dtype=dtype
        )
    expected = 24 * np.arange(0, 35, 7).astype(dtype)
    np.testing.assert_array_equal(result, expected)

    with raise_if_dask_computes():
        if dask:
            time = dask.array.asarray(times[1])
        else:
            time = np.asarray(times[1])
        result = duck_array_ops.datetime_to_numeric(
            time, offset=times[0], datetime_unit="h", dtype=int
        )
    expected = np.array(24 * 7).astype(int)
    np.testing.assert_array_equal(result, expected)


@requires_cftime
def test_datetime_to_numeric_potential_overflow():
    import cftime

    times = pd.date_range("2000", periods=5, freq="7D").values.astype("datetime64[us]")
    cftimes = cftime_range(
        "2000", periods=5, freq="7D", calendar="proleptic_gregorian"
    ).values

    offset = np.datetime64("0001-01-01")
    cfoffset = cftime.DatetimeProlepticGregorian(1, 1, 1)

    result = duck_array_ops.datetime_to_numeric(
        times, offset=offset, datetime_unit="D", dtype=int
    )
    cfresult = duck_array_ops.datetime_to_numeric(
        cftimes, offset=cfoffset, datetime_unit="D", dtype=int
    )

    expected = 730119 + np.arange(0, 35, 7)

    np.testing.assert_array_equal(result, expected)
    np.testing.assert_array_equal(cfresult, expected)


def test_py_timedelta_to_float():
    assert py_timedelta_to_float(dt.timedelta(days=1), "ns") == 86400 * 1e9
    assert py_timedelta_to_float(dt.timedelta(days=1e6), "ps") == 86400 * 1e18
    assert py_timedelta_to_float(dt.timedelta(days=1e6), "ns") == 86400 * 1e15
    assert py_timedelta_to_float(dt.timedelta(days=1e6), "us") == 86400 * 1e12
    assert py_timedelta_to_float(dt.timedelta(days=1e6), "ms") == 86400 * 1e9
    assert py_timedelta_to_float(dt.timedelta(days=1e6), "s") == 86400 * 1e6
    assert py_timedelta_to_float(dt.timedelta(days=1e6), "D") == 1e6


@pytest.mark.parametrize(
    "td, expected",
    ([np.timedelta64(1, "D"), 86400 * 1e9], [np.timedelta64(1, "ns"), 1.0]),
)
def test_np_timedelta64_to_float(td, expected):
    out = np_timedelta64_to_float(td, datetime_unit="ns")
    np.testing.assert_allclose(out, expected)
    assert isinstance(out, float)

    out = np_timedelta64_to_float(np.atleast_1d(td), datetime_unit="ns")
    np.testing.assert_allclose(out, expected)


@pytest.mark.parametrize(
    "td, expected", ([pd.Timedelta(1, "D"), 86400 * 1e9], [pd.Timedelta(1, "ns"), 1.0])
)
def test_pd_timedelta_to_float(td, expected):
    out = pd_timedelta_to_float(td, datetime_unit="ns")
    np.testing.assert_allclose(out, expected)
    assert isinstance(out, float)


@pytest.mark.parametrize(
    "td", [dt.timedelta(days=1), np.timedelta64(1, "D"), pd.Timedelta(1, "D"), "1 day"]
)
def test_timedelta_to_numeric(td):
    # Scalar input
    out = timedelta_to_numeric(td, "ns")
    np.testing.assert_allclose(out, 86400 * 1e9)
    assert isinstance(out, float)


@pytest.mark.parametrize("use_dask", [True, False])
@pytest.mark.parametrize("skipna", [True, False])
def test_least_squares(use_dask, skipna):
    if use_dask and (not has_dask or not has_scipy):
        pytest.skip("requires dask and scipy")
    lhs = np.array([[1, 2], [1, 2], [3, 2]])
    rhs = DataArray(np.array([3, 5, 7]), dims=("y",))

    if use_dask:
        rhs = rhs.chunk({"y": 1})

    coeffs, residuals = least_squares(lhs, rhs.data, skipna=skipna)

    np.testing.assert_allclose(coeffs, [1.5, 1.25])
    np.testing.assert_allclose(residuals, [2.0])


@requires_dask
@requires_bottleneck
def test_push_dask():
    import bottleneck
    import dask.array

    array = np.array([np.nan, 1, 2, 3, np.nan, np.nan, np.nan, np.nan, 4, 5, np.nan, 6])

    for n in [None, 1, 2, 3, 4, 5, 11]:
        expected = bottleneck.push(array, axis=0, n=n)
        for c in range(1, 11):
            with raise_if_dask_computes():
                actual = push(dask.array.from_array(array, chunks=c), axis=0, n=n)
            np.testing.assert_equal(actual, expected)

        # some chunks of size-1 with NaN
        with raise_if_dask_computes():
            actual = push(
                dask.array.from_array(array, chunks=(1, 2, 3, 2, 2, 1, 1)), axis=0, n=n
            )
        np.testing.assert_equal(actual, expected)
