from __future__ import annotations

from itertools import zip_longest
from numbers import Integral

from dask import config
from dask._task_spec import convert_legacy_graph, fuse_linear_task_spec
from dask.blockwise import fuse_roots, optimize_blockwise
from dask.core import flatten
from dask.highlevelgraph import HighLevelGraph
from dask.utils import ensure_dict


def optimize(dsk, keys, **kwargs):
    """Optimize dask for array computation

    1.  Cull tasks not necessary to evaluate keys
    2.  Perform linear fusion
    """
    if not isinstance(keys, (list, set)):
        keys = [keys]
    keys = list(flatten(keys))

    if not isinstance(dsk, HighLevelGraph):
        dsk = HighLevelGraph.from_collections(id(dsk), dsk, dependencies=())

    dsk = optimize_blockwise(dsk, keys=keys)
    dsk = fuse_roots(dsk, keys=keys)
    dsk = dsk.cull(set(keys))

    # Perform low-level fusion unless the user has
    # specified False explicitly.
    if config.get("optimization.fuse.active") is False:
        return dsk

    dsk = ensure_dict(dsk)

    dsk = convert_legacy_graph(dsk)
    dsk = fuse_linear_task_spec(dsk, keys=keys)

    return dsk


def normalize_slice(s):
    """Replace Nones in slices with integers

    >>> normalize_slice(slice(None, None, None))
    slice(0, None, 1)
    """
    start, stop, step = s.start, s.stop, s.step
    if start is None:
        start = 0
    if step is None:
        step = 1
    if start < 0 or step < 0 or stop is not None and stop < 0:
        raise NotImplementedError()
    return slice(start, stop, step)


def check_for_nonfusible_fancy_indexing(fancy, normal):
    # Check for fancy indexing and normal indexing, where the fancy
    # indexed dimensions != normal indexed dimensions with integers. E.g.:
    # disallow things like:
    # x[:, [1, 2], :][0, :, :] -> x[0, [1, 2], :] or
    # x[0, :, :][:, [1, 2], :] -> x[0, [1, 2], :]
    for f, n in zip_longest(fancy, normal, fillvalue=slice(None)):
        if type(f) is not list and isinstance(n, Integral):
            raise NotImplementedError(
                "Can't handle normal indexing with "
                "integers and fancy indexing if the "
                "integers and fancy indices don't "
                "align with the same dimensions."
            )


def fuse_slice(a, b):
    """Fuse stacked slices together

    Fuse a pair of repeated slices into a single slice:

    >>> fuse_slice(slice(1000, 2000), slice(10, 15))
    slice(1010, 1015, None)

    This also works for tuples of slices

    >>> fuse_slice((slice(100, 200), slice(100, 200, 10)),
    ...            (slice(10, 15), [5, 2]))
    (slice(110, 115, None), [150, 120])

    And a variety of other interesting cases

    >>> fuse_slice(slice(1000, 2000), 10)  # integers
    1010

    >>> fuse_slice(slice(1000, 2000, 5), slice(10, 20, 2))
    slice(1050, 1100, 10)

    >>> fuse_slice(slice(1000, 2000, 5), [1, 2, 3])  # lists
    [1005, 1010, 1015]

    >>> fuse_slice(None, slice(None, None))  # doctest: +SKIP
    None
    """
    # None only works if the second side is a full slice
    if a is None and isinstance(b, slice) and b == slice(None, None):
        return None

    # Replace None with 0 and one in start and step
    if isinstance(a, slice):
        a = normalize_slice(a)
    if isinstance(b, slice):
        b = normalize_slice(b)

    if isinstance(a, slice) and isinstance(b, Integral):
        if b < 0:
            raise NotImplementedError()
        return a.start + b * a.step

    if isinstance(a, slice) and isinstance(b, slice):
        start = a.start + a.step * b.start
        if b.stop is not None:
            stop = a.start + a.step * b.stop
        else:
            stop = None
        if a.stop is not None:
            if stop is not None:
                stop = min(a.stop, stop)
            else:
                stop = a.stop
        step = a.step * b.step
        if step == 1:
            step = None
        return slice(start, stop, step)

    if isinstance(b, list):
        return [fuse_slice(a, bb) for bb in b]
    if isinstance(a, list) and isinstance(b, (Integral, slice)):
        return a[b]

    if isinstance(a, tuple) and not isinstance(b, tuple):
        b = (b,)

    # If given two tuples walk through both, being mindful of uneven sizes
    # and newaxes
    if isinstance(a, tuple) and isinstance(b, tuple):
        # Check for non-fusible cases with fancy-indexing
        a_has_lists = any(isinstance(item, list) for item in a)
        b_has_lists = any(isinstance(item, list) for item in b)
        if a_has_lists and b_has_lists:
            raise NotImplementedError("Can't handle multiple list indexing")
        elif a_has_lists:
            check_for_nonfusible_fancy_indexing(a, b)
        elif b_has_lists:
            check_for_nonfusible_fancy_indexing(b, a)

        j = 0
        result = list()
        for i in range(len(a)):
            #  axis ceased to exist  or we're out of b
            if isinstance(a[i], Integral) or j == len(b):
                result.append(a[i])
                continue
            while b[j] is None:  # insert any Nones on the rhs
                result.append(None)
                j += 1
            result.append(fuse_slice(a[i], b[j]))  # Common case
            j += 1
        while j < len(b):  # anything leftover on the right?
            result.append(b[j])
            j += 1
        return tuple(result)
    raise NotImplementedError()