from collections.abc import Hashable, Iterable, Mapping, Sequence
from typing import TYPE_CHECKING, Any, Protocol, overload

try:
    import hypothesis.strategies as st
except ImportError as e:
    raise ImportError(
        "`xarray.testing.strategies` requires `hypothesis` to be installed."
    ) from e

import hypothesis.extra.numpy as npst
import numpy as np
from hypothesis.errors import InvalidArgument

import xarray as xr
from xarray.core.types import T_DuckArray

if TYPE_CHECKING:
    from xarray.core.types import _DTypeLikeNested, _ShapeLike


__all__ = [
    "supported_dtypes",
    "pandas_index_dtypes",
    "names",
    "dimension_names",
    "dimension_sizes",
    "attrs",
    "variables",
    "unique_subset_of",
]


class ArrayStrategyFn(Protocol[T_DuckArray]):
    def __call__(
        self,
        *,
        shape: "_ShapeLike",
        dtype: "_DTypeLikeNested",
    ) -> st.SearchStrategy[T_DuckArray]: ...


def supported_dtypes() -> st.SearchStrategy[np.dtype]:
    """
    Generates only those numpy dtypes which xarray can handle.

    Use instead of hypothesis.extra.numpy.scalar_dtypes in order to exclude weirder dtypes such as unicode, byte_string, array, or nested dtypes.
    Also excludes datetimes, which dodges bugs with pandas non-nanosecond datetime overflows.  Checks only native endianness.

    Requires the hypothesis package to be installed.

    See Also
    --------
    :ref:`testing.hypothesis`_
    """
    # TODO should this be exposed publicly?
    # We should at least decide what the set of numpy dtypes that xarray officially supports is.
    return (
        npst.integer_dtypes(endianness="=")
        | npst.unsigned_integer_dtypes(endianness="=")
        | npst.floating_dtypes(endianness="=")
        | npst.complex_number_dtypes(endianness="=")
        # | npst.datetime64_dtypes()
        # | npst.timedelta64_dtypes()
        # | npst.unicode_string_dtypes()
    )


def pandas_index_dtypes() -> st.SearchStrategy[np.dtype]:
    """
    Dtypes supported by pandas indexes.
    Restrict datetime64 and timedelta64 to ns frequency till Xarray relaxes that.
    """
    return (
        npst.integer_dtypes(endianness="=", sizes=(32, 64))
        | npst.unsigned_integer_dtypes(endianness="=", sizes=(32, 64))
        | npst.floating_dtypes(endianness="=", sizes=(32, 64))
        # TODO: unset max_period
        | npst.datetime64_dtypes(endianness="=", max_period="ns")
        # TODO: set max_period="D"
        | npst.timedelta64_dtypes(endianness="=", max_period="ns")
        | npst.unicode_string_dtypes(endianness="=")
    )


# TODO Generalize to all valid unicode characters once formatting bugs in xarray's reprs are fixed + docs can handle it.
_readable_characters = st.characters(
    categories=["L", "N"], max_codepoint=0x017F
)  # only use characters within the "Latin Extended-A" subset of unicode


def names() -> st.SearchStrategy[str]:
    """
    Generates arbitrary string names for dimensions / variables.

    Requires the hypothesis package to be installed.

    See Also
    --------
    :ref:`testing.hypothesis`_
    """
    return st.text(
        _readable_characters,
        min_size=1,
        max_size=5,
    )


def dimension_names(
    *,
    name_strategy=names(),
    min_dims: int = 0,
    max_dims: int = 3,
) -> st.SearchStrategy[list[Hashable]]:
    """
    Generates an arbitrary list of valid dimension names.

    Requires the hypothesis package to be installed.

    Parameters
    ----------
    name_strategy
        Strategy for making names. Useful if we need to share this.
    min_dims
        Minimum number of dimensions in generated list.
    max_dims
        Maximum number of dimensions in generated list.
    """

    return st.lists(
        elements=name_strategy,
        min_size=min_dims,
        max_size=max_dims,
        unique=True,
    )


def dimension_sizes(
    *,
    dim_names: st.SearchStrategy[Hashable] = names(),
    min_dims: int = 0,
    max_dims: int = 3,
    min_side: int = 1,
    max_side: int | None = None,
) -> st.SearchStrategy[Mapping[Hashable, int]]:
    """
    Generates an arbitrary mapping from dimension names to lengths.

    Requires the hypothesis package to be installed.

    Parameters
    ----------
    dim_names: strategy generating strings, optional
        Strategy for generating dimension names.
        Defaults to the `names` strategy.
    min_dims: int, optional
        Minimum number of dimensions in generated list.
        Default is 1.
    max_dims: int, optional
        Maximum number of dimensions in generated list.
        Default is 3.
    min_side: int, optional
        Minimum size of a dimension.
        Default is 1.
    max_side: int, optional
        Minimum size of a dimension.
        Default is `min_length` + 5.

    See Also
    --------
    :ref:`testing.hypothesis`_
    """

    if max_side is None:
        max_side = min_side + 3

    return st.dictionaries(
        keys=dim_names,
        values=st.integers(min_value=min_side, max_value=max_side),
        min_size=min_dims,
        max_size=max_dims,
    )


_readable_strings = st.text(
    _readable_characters,
    max_size=5,
)
_attr_keys = _readable_strings
_small_arrays = npst.arrays(
    shape=npst.array_shapes(
        max_side=2,
        max_dims=2,
    ),
    dtype=npst.scalar_dtypes()
    | npst.byte_string_dtypes()
    | npst.unicode_string_dtypes(),
)
_attr_values = st.none() | st.booleans() | _readable_strings | _small_arrays

simple_attrs = st.dictionaries(_attr_keys, _attr_values)


def attrs() -> st.SearchStrategy[Mapping[Hashable, Any]]:
    """
    Generates arbitrary valid attributes dictionaries for xarray objects.

    The generated dictionaries can potentially be recursive.

    Requires the hypothesis package to be installed.

    See Also
    --------
    :ref:`testing.hypothesis`_
    """
    return st.recursive(
        st.dictionaries(_attr_keys, _attr_values),
        lambda children: st.dictionaries(_attr_keys, children),
        max_leaves=3,
    )


@st.composite
def variables(
    draw: st.DrawFn,
    *,
    array_strategy_fn: ArrayStrategyFn | None = None,
    dims: st.SearchStrategy[Sequence[Hashable] | Mapping[Hashable, int]] | None = None,
    dtype: st.SearchStrategy[np.dtype] = supported_dtypes(),
    attrs: st.SearchStrategy[Mapping] = attrs(),
) -> xr.Variable:
    """
    Generates arbitrary xarray.Variable objects.

    Follows the basic signature of the xarray.Variable constructor, but allows passing alternative strategies to
    generate either numpy-like array data or dimensions. Also allows specifying the shape or dtype of the wrapped array
    up front.

    Passing nothing will generate a completely arbitrary Variable (containing a numpy array).

    Requires the hypothesis package to be installed.

    Parameters
    ----------
    array_strategy_fn: Callable which returns a strategy generating array-likes, optional
        Callable must only accept shape and dtype kwargs, and must generate results consistent with its input.
        If not passed the default is to generate a small numpy array with one of the supported_dtypes.
    dims: Strategy for generating the dimensions, optional
        Can either be a strategy for generating a sequence of string dimension names,
        or a strategy for generating a mapping of string dimension names to integer lengths along each dimension.
        If provided as a mapping the array shape will be passed to array_strategy_fn.
        Default is to generate arbitrary dimension names for each axis in data.
    dtype: Strategy which generates np.dtype objects, optional
        Will be passed in to array_strategy_fn.
        Default is to generate any scalar dtype using supported_dtypes.
        Be aware that this default set of dtypes includes some not strictly allowed by the array API standard.
    attrs: Strategy which generates dicts, optional
        Default is to generate a nested attributes dictionary containing arbitrary strings, booleans, integers, Nones,
        and numpy arrays.

    Returns
    -------
    variable_strategy
        Strategy for generating xarray.Variable objects.

    Raises
    ------
    ValueError
        If a custom array_strategy_fn returns a strategy which generates an example array inconsistent with the shape
        & dtype input passed to it.

    Examples
    --------
    Generate completely arbitrary Variable objects backed by a numpy array:

    >>> variables().example()  # doctest: +SKIP
    <xarray.Variable (żō: 3)>
    array([43506,   -16,  -151], dtype=int32)
    >>> variables().example()  # doctest: +SKIP
    <xarray.Variable (eD: 4, ğŻżÂĕ: 2, T: 2)>
    array([[[-10000000., -10000000.],
            [-10000000., -10000000.]],
           [[-10000000., -10000000.],
            [        0., -10000000.]],
           [[        0., -10000000.],
            [-10000000.,        inf]],
           [[       -0., -10000000.],
            [-10000000.,        -0.]]], dtype=float32)
    Attributes:
        śřĴ:      {'ĉ': {'iĥf': array([-30117,  -1740], dtype=int16)}}

    Generate only Variable objects with certain dimension names:

    >>> variables(dims=st.just(["a", "b"])).example()  # doctest: +SKIP
    <xarray.Variable (a: 5, b: 3)>
    array([[       248, 4294967295, 4294967295],
           [2412855555, 3514117556, 4294967295],
           [       111, 4294967295, 4294967295],
           [4294967295, 1084434988,      51688],
           [     47714,        252,      11207]], dtype=uint32)

    Generate only Variable objects with certain dimension names and lengths:

    >>> variables(dims=st.just({"a": 2, "b": 1})).example()  # doctest: +SKIP
    <xarray.Variable (a: 2, b: 1)>
    array([[-1.00000000e+007+3.40282347e+038j],
           [-2.75034266e-225+2.22507386e-311j]])

    See Also
    --------
    :ref:`testing.hypothesis`_
    """

    if not isinstance(dims, st.SearchStrategy) and dims is not None:
        raise InvalidArgument(
            f"dims must be provided as a hypothesis.strategies.SearchStrategy object (or None), but got type {type(dims)}. "
            "To specify fixed contents, use hypothesis.strategies.just()."
        )
    if not isinstance(dtype, st.SearchStrategy) and dtype is not None:
        raise InvalidArgument(
            f"dtype must be provided as a hypothesis.strategies.SearchStrategy object (or None), but got type {type(dtype)}. "
            "To specify fixed contents, use hypothesis.strategies.just()."
        )
    if not isinstance(attrs, st.SearchStrategy) and attrs is not None:
        raise InvalidArgument(
            f"attrs must be provided as a hypothesis.strategies.SearchStrategy object (or None), but got type {type(attrs)}. "
            "To specify fixed contents, use hypothesis.strategies.just()."
        )

    _array_strategy_fn: ArrayStrategyFn
    if array_strategy_fn is None:
        # For some reason if I move the default value to the function signature definition mypy incorrectly says the ignore is no longer necessary, making it impossible to satisfy mypy
        _array_strategy_fn = npst.arrays  # type: ignore[assignment]  # npst.arrays has extra kwargs that we aren't using later
    elif not callable(array_strategy_fn):
        raise InvalidArgument(
            "array_strategy_fn must be a Callable that accepts the kwargs dtype and shape and returns a hypothesis "
            "strategy which generates corresponding array-like objects."
        )
    else:
        _array_strategy_fn = (
            array_strategy_fn  # satisfy mypy that this new variable cannot be None
        )

    _dtype = draw(dtype)

    if dims is not None:
        # generate dims first then draw data to match
        _dims = draw(dims)
        if isinstance(_dims, Sequence):
            dim_names = list(_dims)
            valid_shapes = npst.array_shapes(min_dims=len(_dims), max_dims=len(_dims))
            _shape = draw(valid_shapes)
            array_strategy = _array_strategy_fn(shape=_shape, dtype=_dtype)
        elif isinstance(_dims, Mapping | dict):
            # should be a mapping of form {dim_names: lengths}
            dim_names, _shape = list(_dims.keys()), tuple(_dims.values())
            array_strategy = _array_strategy_fn(shape=_shape, dtype=_dtype)
        else:
            raise InvalidArgument(
                f"Invalid type returned by dims strategy - drew an object of type {type(dims)}"
            )
    else:
        # nothing provided, so generate everything consistently
        # We still generate the shape first here just so that we always pass shape to array_strategy_fn
        _shape = draw(npst.array_shapes())
        array_strategy = _array_strategy_fn(shape=_shape, dtype=_dtype)
        dim_names = draw(dimension_names(min_dims=len(_shape), max_dims=len(_shape)))

    _data = draw(array_strategy)

    if _data.shape != _shape:
        raise ValueError(
            "array_strategy_fn returned an array object with a different shape than it was passed."
            f"Passed {_shape}, but returned {_data.shape}."
            "Please either specify a consistent shape via the dims kwarg or ensure the array_strategy_fn callable "
            "obeys the shape argument passed to it."
        )
    if _data.dtype != _dtype:
        raise ValueError(
            "array_strategy_fn returned an array object with a different dtype than it was passed."
            f"Passed {_dtype}, but returned {_data.dtype}"
            "Please either specify a consistent dtype via the dtype kwarg or ensure the array_strategy_fn callable "
            "obeys the dtype argument passed to it."
        )

    return xr.Variable(dims=dim_names, data=_data, attrs=draw(attrs))


@overload
def unique_subset_of(
    objs: Sequence[Hashable],
    *,
    min_size: int = 0,
    max_size: int | None = None,
) -> st.SearchStrategy[Sequence[Hashable]]: ...


@overload
def unique_subset_of(
    objs: Mapping[Hashable, Any],
    *,
    min_size: int = 0,
    max_size: int | None = None,
) -> st.SearchStrategy[Mapping[Hashable, Any]]: ...


@st.composite
def unique_subset_of(
    draw: st.DrawFn,
    objs: Sequence[Hashable] | Mapping[Hashable, Any],
    *,
    min_size: int = 0,
    max_size: int | None = None,
) -> Sequence[Hashable] | Mapping[Hashable, Any]:
    """
    Return a strategy which generates a unique subset of the given objects.

    Each entry in the output subset will be unique (if input was a sequence) or have a unique key (if it was a mapping).

    Requires the hypothesis package to be installed.

    Parameters
    ----------
    objs: Union[Sequence[Hashable], Mapping[Hashable, Any]]
        Objects from which to sample to produce the subset.
    min_size: int, optional
        Minimum size of the returned subset. Default is 0.
    max_size: int, optional
        Maximum size of the returned subset. Default is the full length of the input.
        If set to 0 the result will be an empty mapping.

    Returns
    -------
    unique_subset_strategy
        Strategy generating subset of the input.

    Examples
    --------
    >>> unique_subset_of({"x": 2, "y": 3}).example()  # doctest: +SKIP
    {'y': 3}
    >>> unique_subset_of(["x", "y"]).example()  # doctest: +SKIP
    ['x']

    See Also
    --------
    :ref:`testing.hypothesis`_
    """
    if not isinstance(objs, Iterable):
        raise TypeError(
            f"Object to sample from must be an Iterable or a Mapping, but received type {type(objs)}"
        )

    if len(objs) == 0:
        raise ValueError("Can't sample from a length-zero object.")

    keys = list(objs.keys()) if isinstance(objs, Mapping) else objs

    subset_keys = draw(
        st.lists(
            st.sampled_from(keys),
            unique=True,
            min_size=min_size,
            max_size=max_size,
        )
    )

    return (
        {k: objs[k] for k in subset_keys} if isinstance(objs, Mapping) else subset_keys
    )
