"""
Provide basic components for groupby. These definitions
hold the whitelist of methods that are exposed on the
SeriesGroupBy and the DataFrameGroupBy objects.
"""
import collections

from pandas.core.dtypes.common import is_list_like, is_scalar

OutputKey = collections.namedtuple("OutputKey", ["label", "position"])


class GroupByMixin:
    """
    Provide the groupby facilities to the mixed object.
    """

    def _gotitem(self, key, ndim, subset=None):
        """
        Sub-classes to define. Return a sliced object.

        Parameters
        ----------
        key : string / list of selections
        ndim : 1,2
            requested ndim of result
        subset : object, default None
            subset to act on
        """
        # create a new object to prevent aliasing
        if subset is None:
            subset = self.obj

        # we need to make a shallow copy of ourselves
        # with the same groupby
        kwargs = {attr: getattr(self, attr) for attr in self._attributes}

        # Try to select from a DataFrame, falling back to a Series
        try:
            groupby = self._groupby[key]
        except IndexError:
            groupby = self._groupby

        self = type(self)(subset, groupby=groupby, parent=self, **kwargs)
        self._reset_cache()
        if subset.ndim == 2:
            if is_scalar(key) and key in subset or is_list_like(key):
                self._selection = key
        return self


# special case to prevent duplicate plots when catching exceptions when
# forwarding methods from NDFrames
plotting_methods = frozenset(["plot", "hist"])

common_apply_whitelist = (
    frozenset(
        [
            "quantile",
            "fillna",
            "mad",
            "take",
            "idxmax",
            "idxmin",
            "tshift",
            "skew",
            "corr",
            "cov",
            "diff",
        ]
    )
    | plotting_methods
)

series_apply_whitelist = (
    (
        common_apply_whitelist
        | {
            "nlargest",
            "nsmallest",
            "is_monotonic_increasing",
            "is_monotonic_decreasing",
        }
    )
) | frozenset(["dtype", "unique"])

dataframe_apply_whitelist = common_apply_whitelist | frozenset(["dtypes", "corrwith"])

# cythonized transformations or canned "agg+broadcast", which do not
# require postprocessing of the result by transform.
cythonized_kernels = frozenset(["cumprod", "cumsum", "shift", "cummin", "cummax"])

cython_cast_blacklist = frozenset(["rank", "count", "size", "idxmin", "idxmax"])

# List of aggregation/reduction functions.
# These map each group to a single numeric value
reduction_kernels = frozenset(
    [
        "all",
        "any",
        "count",
        "first",
        "idxmax",
        "idxmin",
        "last",
        "mad",
        "max",
        "mean",
        "median",
        "min",
        "ngroup",
        "nth",
        "nunique",
        "prod",
        # as long as `quantile`'s signature accepts only
        # a single quantile value, it's a reduction.
        # GH#27526 might change that.
        "quantile",
        "sem",
        "size",
        "skew",
        "std",
        "sum",
        "var",
    ]
)

# List of transformation functions.
# a transformation is a function that, for each group,
# produces a result that has the same shape as the group.
transformation_kernels = frozenset(
    [
        "backfill",
        "bfill",
        "corrwith",
        "cumcount",
        "cummax",
        "cummin",
        "cumprod",
        "cumsum",
        "diff",
        "ffill",
        "fillna",
        "pad",
        "pct_change",
        "rank",
        "shift",
        "tshift",
    ]
)

# these are all the public methods on Grouper which don't belong
# in either of the above lists
groupby_other_methods = frozenset(
    [
        "agg",
        "aggregate",
        "apply",
        "boxplot",
        # corr and cov return ngroups*ncolumns rows, so they
        # are neither a transformation nor a reduction
        "corr",
        "cov",
        "describe",
        "dtypes",
        "expanding",
        "filter",
        "get_group",
        "groups",
        "head",
        "hist",
        "indices",
        "ndim",
        "ngroups",
        "ohlc",
        "pipe",
        "plot",
        "resample",
        "rolling",
        "tail",
        "take",
        "transform",
    ]
)
# Valid values  of `name` for `groupby.transform(name)`
# NOTE: do NOT edit this directly. New additions should be inserted
# into the appropriate list above.
transform_kernel_whitelist = reduction_kernels | transformation_kernels