# Licensed under a 3-clause BSD style license - see LICENSE.rst
import operator

import numpy as np
import pytest
from numpy.testing import assert_array_equal

from astropy import units as u
from astropy.coordinates import Angle
from astropy.tests.helper import assert_quantity_allclose
from astropy.uncertainty import distributions as ds
from astropy.uncertainty.core import Distribution
from astropy.utils import NumpyRNGContext
from astropy.utils.compat.numpycompat import NUMPY_LT_1_23
from astropy.utils.compat.optional_deps import HAS_SCIPY

if HAS_SCIPY:
    from scipy.stats import norm  # pylint: disable=W0611

    SMAD_FACTOR = 1 / norm.ppf(0.75)


class TestInit:
    @classmethod
    def setup_class(self):
        self.rates = np.array([1, 5, 30, 400])[:, np.newaxis]
        self.parr = np.random.poisson(self.rates, (4, 1000))
        self.parr_t = np.random.poisson(self.rates.squeeze(), (1000, 4))

    def test_numpy_init(self):
        # Test that we can initialize directly from a Numpy array
        Distribution(self.parr)

    def test_numpy_init_T(self):
        Distribution(self.parr_t.T)

    def test_quantity_init(self):
        # Test that we can initialize directly from a Quantity
        pq = self.parr << u.ct
        pqd = Distribution(pq)
        assert isinstance(pqd, u.Quantity)
        assert isinstance(pqd, Distribution)
        assert isinstance(pqd.value, Distribution)
        assert_array_equal(pqd.value.distribution, self.parr)

    def test_quantity_init_T(self):
        # Test that we can initialize directly from a Quantity
        pq = self.parr_t << u.ct
        Distribution(pq.T)

    def test_quantity_init_with_distribution(self):
        # Test that we can initialize a Quantity from a Distribution.
        pd = Distribution(self.parr)
        qpd = pd << u.ct
        assert isinstance(qpd, u.Quantity)
        assert isinstance(qpd, Distribution)
        assert qpd.unit == u.ct
        assert_array_equal(qpd.value.distribution, pd.distribution.astype(float))


def test_init_scalar():
    parr = np.random.poisson(np.array([1, 5, 30, 400])[:, np.newaxis], (4, 1000))
    with pytest.raises(
        TypeError, match=r"Attempted to initialize a Distribution with a scalar"
    ):
        Distribution(parr.ravel()[0])


class TestDistributionStatistics:
    def setup_class(self):
        with NumpyRNGContext(12345):
            self.data = np.random.normal(
                np.array([1, 2, 3, 4])[:, np.newaxis],
                np.array([3, 2, 4, 5])[:, np.newaxis],
                (4, 10000),
            )

        self.distr = Distribution(self.data * u.kpc)

    def test_shape(self):
        # Distribution shape
        assert self.distr.shape == (4,)
        assert self.distr.distribution.shape == (4, 10000)

    def test_size(self):
        # Total number of values
        assert self.distr.size == 4
        assert self.distr.distribution.size == 40000

    def test_n_samples(self):
        # Number of samples
        assert self.distr.n_samples == 10000

    def test_n_distr(self):
        assert self.distr.shape == (4,)

    def test_pdf_mean(self):
        # Mean of each PDF
        expected = np.mean(self.data, axis=-1) * self.distr.unit
        pdf_mean = self.distr.pdf_mean()
        assert_quantity_allclose(pdf_mean, expected)
        assert_quantity_allclose(pdf_mean, [1, 2, 3, 4] * self.distr.unit, rtol=0.05)

        # make sure the right type comes out - should be a Quantity because it's
        # now a summary statistic
        assert not isinstance(pdf_mean, Distribution)
        assert isinstance(pdf_mean, u.Quantity)

        # Check with out argument.
        out = pdf_mean * 0.0
        pdf_mean2 = self.distr.pdf_mean(out=out)
        assert pdf_mean2 is out
        assert np.all(pdf_mean2 == pdf_mean)

    def test_pdf_std(self):
        # Standard deviation of each PDF
        expected = np.std(self.data, axis=-1) * self.distr.unit
        pdf_std = self.distr.pdf_std()
        assert_quantity_allclose(pdf_std, expected)
        assert_quantity_allclose(pdf_std, [3, 2, 4, 5] * self.distr.unit, rtol=0.05)

        # make sure the right type comes out - should be a Quantity because it's
        # now a summary statistic
        assert not isinstance(pdf_std, Distribution)
        assert isinstance(pdf_std, u.Quantity)

        # Check with proper ddof, using out argument.
        out = pdf_std * 0.0
        expected = np.std(self.data, axis=-1, ddof=1) * self.distr.unit
        pdf_std2 = self.distr.pdf_std(ddof=1, out=out)
        assert pdf_std2 is out
        assert np.all(pdf_std2 == expected)

    def test_pdf_var(self):
        # Variance of each PDF
        expected = np.var(self.data, axis=-1) * self.distr.unit**2
        pdf_var = self.distr.pdf_var()
        assert_quantity_allclose(pdf_var, expected)
        assert_quantity_allclose(
            pdf_var, [9, 4, 16, 25] * self.distr.unit**2, rtol=0.1
        )

        # make sure the right type comes out - should be a Quantity because it's
        # now a summary statistic
        assert not isinstance(pdf_var, Distribution)
        assert isinstance(pdf_var, u.Quantity)

        # Check with proper ddof, using out argument.
        out = pdf_var * 0.0
        expected = np.var(self.data, axis=-1, ddof=1) * self.distr.unit**2
        pdf_var2 = self.distr.pdf_var(ddof=1, out=out)
        assert pdf_var2 is out
        assert np.all(pdf_var2 == expected)

    def test_pdf_median(self):
        # Median of each PDF
        expected = np.median(self.data, axis=-1) * self.distr.unit
        pdf_median = self.distr.pdf_median()
        assert_quantity_allclose(pdf_median, expected)
        assert_quantity_allclose(pdf_median, [1, 2, 3, 4] * self.distr.unit, rtol=0.1)

        # make sure the right type comes out - should be a Quantity because it's
        # now a summary statistic
        assert not isinstance(pdf_median, Distribution)
        assert isinstance(pdf_median, u.Quantity)

        # Check with out argument.
        out = pdf_median * 0.0
        pdf_median2 = self.distr.pdf_median(out=out)
        assert pdf_median2 is out
        assert np.all(pdf_median2 == expected)

    @pytest.mark.skipif(not HAS_SCIPY, reason="no scipy")
    def test_pdf_mad_smad(self):
        # Median absolute deviation of each PDF
        median = np.median(self.data, axis=-1, keepdims=True)
        expected = np.median(np.abs(self.data - median), axis=-1) * self.distr.unit
        pdf_mad = self.distr.pdf_mad()
        assert_quantity_allclose(pdf_mad, expected)
        pdf_smad = self.distr.pdf_smad()
        assert_quantity_allclose(pdf_smad, pdf_mad * SMAD_FACTOR, rtol=1e-5)
        assert_quantity_allclose(pdf_smad, [3, 2, 4, 5] * self.distr.unit, rtol=0.05)

        # make sure the right type comes out - should be a Quantity because it's
        # now a summary statistic
        assert not isinstance(pdf_mad, Distribution)
        assert isinstance(pdf_mad, u.Quantity)
        assert not isinstance(pdf_smad, Distribution)
        assert isinstance(pdf_smad, u.Quantity)

        # Check out argument for smad (which checks mad too).
        out = pdf_smad * 0.0
        pdf_smad2 = self.distr.pdf_smad(out=out)
        assert pdf_smad2 is out
        assert np.all(pdf_smad2 == pdf_smad)

    def test_percentile(self):
        expected = np.percentile(self.data, [10, 50, 90], axis=-1) * self.distr.unit
        percs = self.distr.pdf_percentiles([10, 50, 90])
        assert_quantity_allclose(percs, expected)
        assert percs.shape == (3, 4)

        # make sure the right type comes out - should be a Quantity because it's
        # now a summary statistic
        assert not isinstance(percs, Distribution)
        assert isinstance(percs, u.Quantity)

    def test_add_quantity(self):
        distrplus = self.distr + [2000, 0, 0, 500] * u.pc
        expected = (
            np.median(self.data, axis=-1) + np.array([2, 0, 0, 0.5])
        ) * self.distr.unit
        assert_quantity_allclose(distrplus.pdf_median(), expected)
        expected = np.var(self.data, axis=-1) * self.distr.unit**2
        assert_quantity_allclose(distrplus.pdf_var(), expected)

    def test_add_distribution(self):
        another_data = (
            np.random.randn(4, 10000) * np.array([1000, 0.01, 80, 10])[:, np.newaxis]
            + np.array([2000, 0, 0, 500])[:, np.newaxis]
        )
        # another_data is in pc, but main distr is in kpc
        another_distr = Distribution(another_data * u.pc)
        combined_distr = self.distr + another_distr

        expected = np.median(self.data + another_data / 1000, axis=-1) * self.distr.unit
        assert_quantity_allclose(combined_distr.pdf_median(), expected)

        expected = (
            np.var(self.data + another_data / 1000, axis=-1) * self.distr.unit**2
        )
        assert_quantity_allclose(combined_distr.pdf_var(), expected)


def test_helper_normal_samples():
    centerq = [1, 5, 30, 400] * u.kpc

    with NumpyRNGContext(12345):
        n_dist = ds.normal(centerq, std=[0.2, 1.5, 4, 1] * u.kpc, n_samples=100)
        assert n_dist.distribution.shape == (4, 100)
        assert n_dist.shape == (4,)
        assert n_dist.unit == u.kpc
        assert np.all(n_dist.pdf_std() > 100 * u.pc)

        n_dist2 = ds.normal(centerq, std=[0.2, 1.5, 4, 1] * u.pc, n_samples=20000)
        assert n_dist2.distribution.shape == (4, 20000)
        assert n_dist2.shape == (4,)
        assert n_dist2.unit == u.kpc
        assert np.all(n_dist2.pdf_std() < 100 * u.pc)


def test_helper_poisson_samples():
    centerqcounts = [1, 5, 30, 400] * u.count

    with NumpyRNGContext(12345):
        p_dist = ds.poisson(centerqcounts, n_samples=100)
        assert p_dist.shape == (4,)
        assert p_dist.distribution.shape == (4, 100)
        assert p_dist.unit == u.count
        p_min = np.min(p_dist)
        assert isinstance(p_min, Distribution)
        assert p_min.shape == ()
        assert np.all(p_min >= 0)
        assert np.all(np.abs(p_dist.pdf_mean() - centerqcounts) < centerqcounts)


def test_helper_uniform_samples():
    udist = ds.uniform(lower=[1, 2] * u.kpc, upper=[3, 4] * u.kpc, n_samples=1000)
    assert udist.shape == (2,)
    assert udist.distribution.shape == (2, 1000)
    assert np.all(np.min(udist.distribution, axis=-1) > [1, 2] * u.kpc)
    assert np.all(np.max(udist.distribution, axis=-1) < [3, 4] * u.kpc)

    # try the alternative creator
    udist = ds.uniform(center=[1, 3, 2] * u.pc, width=[5, 4, 3] * u.pc, n_samples=1000)
    assert udist.shape == (3,)
    assert udist.distribution.shape == (3, 1000)
    assert np.all(np.min(udist.distribution, axis=-1) > [-1.5, 1, 0.5] * u.pc)
    assert np.all(np.max(udist.distribution, axis=-1) < [3.5, 5, 3.5] * u.pc)


def test_helper_normal_exact():
    pytest.skip("distribution stretch goal not yet implemented")
    centerq = [1, 5, 30, 400] * u.kpc
    ds.normal(centerq, std=[0.2, 1.5, 4, 1] * u.kpc)
    ds.normal(centerq, var=[0.04, 2.25, 16, 1] * u.kpc**2)
    ds.normal(centerq, ivar=[25, 0.44444444, 0.625, 1] * u.kpc**-2)


def test_helper_poisson_exact():
    pytest.skip("distribution stretch goal not yet implemented")
    centerq = [1, 5, 30, 400] * u.one
    ds.poisson(centerq, n_samples=1000)

    with pytest.raises(
        u.UnitsError,
        match=r"Poisson distribution can only be computed for dimensionless quantities",
    ):
        centerq = [1, 5, 30, 400] * u.kpc
        ds.poisson(centerq, n_samples=1000)


def test_reprs():
    darr = np.arange(30).reshape(3, 10)
    distr = Distribution(darr * u.kpc)

    assert "n_samples=10" in repr(distr)
    assert "n_samples=10" in str(distr)

    assert r"n_{\rm samp}=10" in distr._repr_latex_()


@pytest.mark.parametrize(
    "func, kws",
    [
        (ds.normal, {"center": 0, "std": 2}),
        (ds.uniform, {"lower": 0, "upper": 2}),
        (ds.poisson, {"center": 2}),
        (ds.normal, {"center": 0 * u.count, "std": 2 * u.count}),
        (ds.uniform, {"lower": 0 * u.count, "upper": 2 * u.count}),
        (ds.poisson, {"center": 2 * u.count}),
    ],
)
def test_wrong_kw_fails(func, kws):
    with pytest.raises(TypeError, match="missing 1 required"):
        kw_temp = kws.copy()
        kw_temp["n_sample"] = 100  # note the missing "s"
        assert func(**kw_temp).n_samples == 100
    kw_temp = kws.copy()
    kw_temp["n_samples"] = 100
    assert func(**kw_temp).n_samples == 100


def test_index_assignment_quantity():
    arr = np.random.randn(2, 1000)
    distr = Distribution(arr * u.kpc)
    d1q, d2q = distr
    assert isinstance(d1q, Distribution)
    assert isinstance(d2q, Distribution)

    ndistr = ds.normal(center=[1, 2] * u.kpc, std=[3, 4] * u.kpc, n_samples=1000)
    n1, n2 = ndistr
    assert isinstance(n1, ds.Distribution)
    assert isinstance(n2, ds.Distribution)


def test_index_assignment_array():
    arr = np.random.randn(2, 1000)
    distr = Distribution(arr)
    d1a, d2a = distr
    assert isinstance(d1a, Distribution)
    assert isinstance(d2a, Distribution)

    ndistr = ds.normal(center=[1, 2], std=[3, 4], n_samples=1000)
    n1, n2 = ndistr
    assert isinstance(n1, ds.Distribution)
    assert isinstance(n2, ds.Distribution)


def test_histogram():
    arr = np.random.randn(2, 3, 1000)
    distr = Distribution(arr)

    hist, bins = distr.pdf_histogram(bins=10)
    assert hist.shape == (2, 3, 10)
    assert bins.shape == (2, 3, 11)


def test_array_repr_latex():
    # as of this writing ndarray does not have a _repr_latex_, and this test
    # ensure distributions account for that. However, if in the future ndarray
    # gets a _repr_latex_, we can skip this.

    arr = np.random.randn(4, 1000)

    if hasattr(arr, "_repr_latex_"):
        pytest.skip("in this version of numpy, ndarray has a _repr_latex_")

    distr = Distribution(arr)
    assert distr._repr_latex_() is None


def test_distr_to():
    distr = ds.normal(10 * u.cm, n_samples=100, std=1 * u.cm)
    todistr = distr.to(u.m)
    assert_quantity_allclose(distr.pdf_mean().to(u.m), todistr.pdf_mean())


def test_distr_noq_to():
    # this is an array distribution not a quantity
    distr = ds.normal(10, n_samples=100, std=1)
    with pytest.raises(AttributeError):
        distr.to(u.m)


def test_distr_to_value():
    distr = ds.normal(10 * u.cm, n_samples=100, std=1 * u.cm)
    tovdistr = distr.to_value(u.m)
    assert np.allclose(distr.pdf_mean().to_value(u.m), tovdistr.pdf_mean())


def test_distr_noq_to_value():
    distr = ds.normal(10, n_samples=100, std=1)
    with pytest.raises(AttributeError):
        distr.to_value(u.m)


def test_distr_angle():
    # Check that Quantity subclasses decay to Quantity appropriately.
    distr = Distribution([2.0, 3.0, 4.0])
    ad = Angle(distr, "deg")
    ad_plus_ad = ad + ad
    assert isinstance(ad_plus_ad, Angle)
    assert isinstance(ad_plus_ad, Distribution)

    ad_times_ad = ad * ad
    assert not isinstance(ad_times_ad, Angle)
    assert isinstance(ad_times_ad, u.Quantity)
    assert isinstance(ad_times_ad, Distribution)

    ad += ad
    assert isinstance(ad, Angle)
    assert isinstance(ad, Distribution)
    assert_array_equal(ad.distribution, ad_plus_ad.distribution)

    with pytest.raises(u.UnitTypeError):
        ad *= ad


def test_distr_angle_view_as_quantity():
    # Check that Quantity subclasses decay to Quantity appropriately.
    distr = Distribution([2.0, 3.0, 4.0])
    ad = Angle(distr, "deg")
    qd = ad.view(u.Quantity)
    assert not isinstance(qd, Angle)
    assert isinstance(qd, u.Quantity)
    assert isinstance(qd, Distribution)
    # View directly as DistributionQuantity class.
    qd2 = ad.view(qd.__class__)
    assert not isinstance(qd2, Angle)
    assert isinstance(qd2, u.Quantity)
    assert isinstance(qd2, Distribution)
    assert_array_equal(qd2.distribution, qd.distribution)
    qd3 = ad.view(qd.dtype, qd.__class__)
    assert not isinstance(qd3, Angle)
    assert isinstance(qd3, u.Quantity)
    assert isinstance(qd3, Distribution)
    assert_array_equal(qd3.distribution, qd.distribution)
    # Simple view with no arguments
    qd4 = qd3.view()
    assert qd4.__class__ is qd3.__class__
    assert np.may_share_memory(qd4, qd3)


def test_distr_view_different_dtype1():
    # Viewing with a new dtype should follow the same rules as for a
    # regular array with the same dtype.
    c = Distribution([2.0j, 3.0, 4.0j])
    r = c.view("2f8")
    assert r.shape == c.shape + (2,)
    assert np.may_share_memory(r, c)
    expected = np.moveaxis(c.distribution.view("2f8"), -2, -1)
    assert_array_equal(r.distribution, expected)
    c2 = r.view("c16")
    assert_array_equal(c2.distribution, c.distribution)
    assert np.may_share_memory(c2, c)


def test_distr_view_different_dtype2():
    # Viewing with a new dtype should follow the same rules as for a
    # regular array with the same dtype.
    uint32 = Distribution(
        np.array([[0x01020304, 0x05060708], [0x11121314, 0x15161718]], dtype="u4")
    )
    uint8 = uint32.view("4u1")
    assert uint8.shape == uint32.shape + (4,)
    assert np.may_share_memory(uint8, uint32)
    expected = np.moveaxis(uint32.distribution.view("4u1"), -2, -1)
    assert_array_equal(uint8.distribution, expected)
    uint32_2 = uint8.view("u4")
    assert np.may_share_memory(uint32_2, uint32)
    assert_array_equal(uint32_2.distribution, uint32.distribution)
    uint8_2 = uint8.T
    if NUMPY_LT_1_23:
        with pytest.raises(DeprecationWarning, match="Changing the shape of an F-"):
            uint8_2.view("u4")
    else:
        with pytest.raises(ValueError, match="last axis must be contiguous"):
            uint8_2.view("u4")


def test_distr_cannot_view_new_dtype():
    # A Distribution has a very specific structured dtype with just one
    # element that holds the array of samples.  As it is not clear what
    # to do with a view as a new dtype, we just error on it.
    # TODO: with a lot of thought, this restriction can likely be relaxed.
    distr = Distribution([2.0, 3.0, 4.0])
    with pytest.raises(ValueError, match="can only be viewed"):
        distr.view(np.dtype("2i8"))

    with pytest.raises(ValueError, match="can only be viewed"):
        distr.view(np.dtype("2i8"), distr.__class__)

    # Check subclass just in case.
    ad = Angle(distr, "deg")
    with pytest.raises(ValueError, match="can only be viewed"):
        ad.view(np.dtype("2i8"))
    with pytest.raises(ValueError, match="can only be viewed"):
        ad.view("2i8", distr.__class__)


def test_scalar_quantity_distribution():
    # Regression test for gh-12336
    angles = Distribution([90.0, 30.0, 0.0] * u.deg)
    sin_angles = np.sin(angles)  # This failed in 4.3.
    assert isinstance(sin_angles, Distribution)
    assert isinstance(sin_angles, u.Quantity)
    assert_array_equal(sin_angles, Distribution(np.sin([90.0, 30.0, 0.0] * u.deg)))


@pytest.mark.parametrize("op", [operator.eq, operator.ne, operator.gt])
class TestComparison:
    @classmethod
    def setup_class(cls):
        cls.d = Distribution([90.0, 30.0, 0.0])

        class Override:
            __array_ufunc__ = None

            def __eq__(self, other):
                return "eq"

            def __ne__(self, other):
                return "ne"

            def __lt__(self, other):
                return "gt"  # Since it is called for the reverse of gt

        cls.override = Override()

    def test_distribution_can_be_compared_to_non_distribution(self, op):
        result = op(self.d, 0.0)
        assert_array_equal(result, Distribution(op(self.d.distribution, 0.0)))

    def test_distribution_comparison_defers_correctly(self, op):
        result = op(self.d, self.override)
        assert result == op.__name__


class TestSetItemWithSelection:
    def test_setitem(self):
        d = Distribution([90.0, 30.0, 0.0])
        d[d > 50] = 0.0
        assert_array_equal(d, Distribution([0.0, 30.0, 0.0]))

    def test_inplace_operation(self):
        d = Distribution([90.0, 30.0, 0.0])
        d[d > 50] *= -1.0
        assert_array_equal(d, Distribution([-90.0, 30.0, 0.0]))


ADVANCED_INDICES = [
    (np.array([[1, 2], [0, 1]]), np.array([[1, 3], [0, 2]])),
    # Same advanced index, but also using negative numbers
    (np.array([[-2, -1], [0, -2]]), np.array([[1, -1], [-4, -2]])),
]


class TestGetSetItemAdvancedIndex:
    @classmethod
    def setup_class(self):
        self.distribution = np.arange(60.0).reshape(3, 4, 5)
        self.d = Distribution(self.distribution)

    def test_setup(self):
        ai1, ai2 = ADVANCED_INDICES[:2]
        # Check that the first two indices produce the same output.
        assert_array_equal(self.distribution[ai1], self.distribution[ai2])

    @pytest.mark.parametrize("item", ADVANCED_INDICES)
    def test_getitem(self, item):
        v = self.d[item]
        assert v.shape == item[0].shape
        assert_array_equal(v.distribution, self.distribution[item])

    @pytest.mark.parametrize("item", [([0, 4],), ([0], [0], [0])])
    def test_getitem_bad(self, item):
        with pytest.raises(IndexError):
            self.d[item]

    @pytest.mark.parametrize("item", ADVANCED_INDICES)
    def test_setitem(self, item):
        d = self.d.copy()
        d[item] = 0.0
        distribution = self.distribution.copy()
        distribution[item] = 0.0
        assert_array_equal(d.distribution, distribution)
        d[item] = self.d[item]
        assert_array_equal(d.distribution, self.distribution)


class TestQuantityDistributionGetSetItemAdvancedIndex(TestGetSetItemAdvancedIndex):
    @classmethod
    def setup_class(self):
        self.distribution = np.arange(60.0).reshape(3, 4, 5) << u.m
        self.d = Distribution(self.distribution)


class StructuredDtypeBase:
    @classmethod
    def setup_class(self):
        self.dtype = np.dtype([("a", "f8"), ("b", "(2,2)f8")])
        data = np.arange(5.0) + (np.arange(60.0) * 10).reshape(3, 4, 5, 1)
        self.distribution = data.view(self.dtype).reshape(3, 4, 5)
        self.d = Distribution(self.distribution)


class TestStructuredQuantityDistributionInit(StructuredDtypeBase):
    @classmethod
    def setup_class(self):
        super().setup_class()
        self.unit = u.Unit("km, m")
        self.d_unit = self.unit

    def test_init_via_structured_samples(self):
        distribution = self.distribution << self.unit
        d = Distribution(distribution)
        assert d.unit == self.d_unit
        assert_array_equal(d.distribution, distribution)
        assert_array_equal(d.value.distribution, self.distribution)

    def test_init_via_structured_distribution(self):
        d = self.d << self.unit
        assert d.unit == self.d_unit


class TestStructuredAdvancedIndex(StructuredDtypeBase, TestGetSetItemAdvancedIndex):
    def test_init(self):
        assert self.d.shape == (3, 4)
        assert self.d.n_samples == 5
        assert_array_equal(self.d.distribution, self.distribution)


class TestStructuredDistribution(StructuredDtypeBase):
    @classmethod
    def setup_class(self):
        super().setup_class()
        self.item = (0.0, [[-1.0, -2.0], [-3.0, -4.0]])
        self.b_item = [[-1.0, -2.0], [-3.0, -4.0]]

    @pytest.mark.parametrize("item", [-2, slice(1, 3), "a", "b"])
    def test_getitem(self, item):
        d_i = self.d[item]
        assert isinstance(d_i, Distribution)
        if item in self.dtype.names:
            assert d_i.shape == self.d.shape + self.dtype[item].shape
        else:
            assert d_i.shape == np.ones(self.d.shape)[item].shape
        assert np.may_share_memory(d_i, self.d)
        expected = self.distribution[item]
        if isinstance(item, str):
            # Sample axis should always be at the end.
            expected = np.moveaxis(self.distribution[item], self.d.ndim, -1)
        assert_array_equal(d_i.distribution, expected)

    @pytest.mark.parametrize("item", [1, slice(0, 2)])
    def test_setitem_index_slice(self, item):
        d = self.d.copy()
        distribution = self.distribution.copy()
        value = self.item
        d[item] = value
        distribution[item] = value
        assert_array_equal(d.distribution, distribution)
        d[item] = self.d[item]
        assert_array_equal(d.distribution, self.distribution)

    @pytest.mark.parametrize("item", ["a", "b"])
    def test_setitem_field(self, item):
        d = self.d.copy()
        d[item] = 0.0
        assert_array_equal(d.distribution[item], np.zeros_like(self.distribution[item]))
        if item == "b":
            value = self.b_item  # selected to be a bit tricky.
            d[item] = value
            assert_array_equal(
                d.distribution[item], np.full_like(self.distribution[item], value)
            )
        d[item] = self.d[item] * 2.0
        assert_array_equal(d.distribution[item], self.distribution[item] * 2)


class TestStructuredQuantityDistribution(TestStructuredDistribution):
    @classmethod
    def setup_class(self):
        super().setup_class()
        self.distribution = self.distribution * u.Unit("km,m")
        self.d = self.d * u.Unit("km,m")
        self.item = self.item * u.Unit("Mm,km")
        self.b_item = self.b_item * u.km
