import math

import cupy


def float_factorial(n):
    """Compute the factorial and return as a float

    Returns infinity when result is too large for a double
    """
    return float(math.factorial(n)) if n < 171 else cupy.inf


def _asarray_validated(a, check_finite=True,
                       sparse_ok=False, objects_ok=False, mask_ok=False,
                       as_inexact=False):
    """Helper function for SciPy argument validation.

    Many CuPy linear algebra functions do support arbitrary array-like
    input arguments. Examples of commonly unsupported inputs include
    matrices containing inf/nan, sparse matrix representations, and
    matrices with complicated elements.

    Parameters
    ----------
    a : array-like
        The array-like input
    check_finite : bool, optional
        By default True. To check whether the input matrices contain
        only finite numbers. Disabling may give a performance gain,
        but may result in problems (crashes, non-termination) if the
        inputs do contain infinites or NaNs
    sparse_ok : bool, optional
        By default False. True if cupy sparse matrices are allowed
    objects_ok : bool, optional
        By default False. True if arrays with dype('O') are allowed
    mask_ok : bool, optional
        By default False. True if masked arrays are allowed.
    as_inexact : bool, optional
        By default False. True to convert the input array to a
        cupy.inexact dtype

    Returns
    -------
    ret : cupy.ndarray
        The converted validated array

    """

    if not sparse_ok:
        import cupyx.scipy.sparse
        if cupyx.scipy.sparse.issparse(a):
            msg = ('Sparse matrices are not supported by this function. '
                   'Perhaps one of the cupyx.scipy.sparse.linalg functions '
                   'would work instead.')
            raise ValueError(msg)

    # TODO: remove these comments when CuPy supports masked arrays
    # Ref Issue: https://github.com/cupy/cupy/issues/2225
    # if not mask_ok:
    #     if cupy.ma.isMaskedArray(a):
    #         raise ValueError('masked arrays are not supported')

    # TODO: remove these comments when CuPy supports 'object' dtype
    # if not objects_ok:
    #    if a.dtype is cupy.dtype('O'):
    #        raise ValueError('object arrays are not supported')

    if as_inexact:
        if not cupy.issubdtype(a, cupy.inexact):
            a = a.astype(dtype=cupy.float_)

    return a