# BSD 3-Clause License; see https://github.com/scikit-hep/awkward-1.0/blob/main/LICENSE

import awkward as ak

np = ak.nplike.NumpyMetadata.instance()


def count(array, axis=None, keepdims=False, mask_identity=False, flatten_records=False):
    """
    Args:
        array: Array-like data (anything #ak.to_layout recognizes).
        axis (None or int): If None, combine all values from the array into
            a single scalar result; if an int, group by that axis: `0` is the
            outermost, `1` is the first level of nested lists, etc., and
            negative `axis` counts from the innermost: `-1` is the innermost,
            `-2` is the next level up, etc.
        keepdims (bool): If False, this reducer decreases the number of
            dimensions by 1; if True, the reduced values are wrapped in a new
            length-1 dimension so that the result of this operation may be
            broadcasted with the original array.
        mask_identity (bool): If True, reducing over empty lists results in
            None (an option type); otherwise, reducing over empty lists
            results in the operation's identity.
        flatten_records (bool): If True, axis=None combines fields from different
            records; otherwise, records raise an error.

    Counts elements of `array` (many types supported, including all
    Awkward Arrays and Records). The identity of counting is `0` and it is
    usually not masked.

    This function has no analog in NumPy because counting values in a
    rectilinear array would only result in elements of the NumPy array's
    [shape](https://docs.scipy.org/doc/numpy/reference/generated/numpy.ndarray.shape.html).

    However, for nested lists of variable dimension and missing values, the
    result of counting is non-trivial. For example, with this `array`,

        ak.Array([[ 0.1,  0.2      ],
                  [None, 10.2, None],
                  None,
                  [20.1, 20.2, 20.3],
                  [30.1, 30.2      ]])

    the result of counting over the innermost dimension is

        >>> ak.count(array, axis=-1)
        <Array [2, 1, None, 3, 2] type='5 * ?int64'>

    the outermost dimension is

        >>> ak.count(array, axis=0)
        <Array [3, 4, 1] type='3 * int64'>

    and all dimensions is

        >>> ak.count(array, axis=None)
        8

    The gaps and None values are not counted, and if a None value occurs at
    a higher axis than the one being counted, it is kept as a placeholder
    so that the outer list length does not change.

    See #ak.sum for a more complete description of nested list and missing
    value (None) handling in reducers.

    Note also that this function is different from #ak.num, which counts
    the number of values at a given depth, maintaining structure: #ak.num
    never counts across different lists the way that reducers do (#ak.num
    is not a reducer; #ak.count is). For the same `array`,

        >>> ak.num(array, axis=0)
        5
        >>> ak.num(array, axis=1)
        <Array [2, 3, None, 3, 2] type='5 * ?int64'>

    If it is desirable to include None values in #ak.count, use #ak.fill_none
    to turn the None values into something that would be counted.
    """
    layout = ak._v2.operations.convert.to_layout(
        array, allow_record=False, allow_other=False
    )

    if axis is None:

        def reduce(xs):
            if len(xs) == 1:
                return xs[0]
            else:
                return layout.nplike.add(xs[0], reduce(xs[1:]))

        return reduce(
            [
                layout.nplike.size(x)
                for x in layout.completely_flatten(
                    function_name="ak.count", flatten_records=flatten_records
                )
            ]
        )

    else:
        behavior = ak._v2._util.behavior_of(array)
        out = layout.count(axis=axis, mask=mask_identity, keepdims=keepdims)
        if isinstance(out, (ak._v2.contents.Content, ak._v2.record.Record)):
            return ak._v2._util.wrap(out, behavior)
        else:
            return out
