from __future__ import annotations

import functools
import math
import operator
from collections import defaultdict
from collections.abc import Callable
from itertools import product
from typing import Any

import tlz as toolz
from tlz.curried import map

from dask.base import tokenize
from dask.blockwise import Blockwise, BlockwiseDep, BlockwiseDepDict, blockwise_token
from dask.core import flatten
from dask.highlevelgraph import Layer
from dask.utils import apply, cached_cumsum, concrete, insert

#
##
###  General Utilities
##
#


class CallableLazyImport:
    """Function Wrapper for Lazy Importing.

    This Class should only be used when materializing a graph
    on a distributed scheduler.
    """

    def __init__(self, function_path):
        self.function_path = function_path

    def __call__(self, *args, **kwargs):
        from distributed.utils import import_term

        return import_term(self.function_path)(*args, **kwargs)


#
##
###  Array Layers & Utilities
##
#


class ArrayBlockwiseDep(BlockwiseDep):
    """
    Blockwise dep for array-likes, which only needs chunking
    information to compute its data.
    """

    chunks: tuple[tuple[int, ...], ...]
    numblocks: tuple[int, ...]
    produces_tasks: bool = False

    def __init__(self, chunks: tuple[tuple[int, ...], ...]):
        self.chunks = chunks
        self.numblocks = tuple(len(chunk) for chunk in chunks)
        self.produces_tasks = False

    def __getitem__(self, idx: tuple[int, ...]):
        raise NotImplementedError("Subclasses must implement __getitem__")


class ArrayChunkShapeDep(ArrayBlockwiseDep):
    """Produce chunk shapes given a chunk index"""

    def __getitem__(self, idx: tuple[int, ...]):
        return tuple(chunk[i] for i, chunk in zip(idx, self.chunks))


class ArraySliceDep(ArrayBlockwiseDep):
    """Produce slice(s) into the full-sized array given a chunk index"""

    starts: tuple[tuple[int, ...], ...]

    def __init__(self, chunks: tuple[tuple[int, ...], ...]):
        super().__init__(chunks)
        self.starts = tuple(cached_cumsum(c, initial_zero=True) for c in chunks)

    def __getitem__(self, idx: tuple):
        loc = tuple((start[i], start[i + 1]) for i, start in zip(idx, self.starts))
        return tuple(slice(*s, None) for s in loc)


class ArrayOverlapLayer(Layer):
    """Simple HighLevelGraph array overlap layer.

    Lazily computed High-level graph layer for a array overlap operations.

    Parameters
    ----------
    name : str
        Name of new output overlap array.
    array : Dask array
    axes: Mapping
        Axes dictionary indicating overlap in each dimension,
        e.g. ``{'0': 1, '1': 1}``
    """

    def __init__(
        self,
        name,
        axes,
        chunks,
        numblocks,
        token,
    ):
        super().__init__()
        self.name = name
        self.axes = axes
        self.chunks = chunks
        self.numblocks = numblocks
        self.token = token
        self._cached_keys = None

    def __repr__(self):
        return f"ArrayOverlapLayer<name='{self.name}'"

    @property
    def _dict(self):
        """Materialize full dict representation"""
        if hasattr(self, "_cached_dict"):
            return self._cached_dict
        else:
            dsk = self._construct_graph()
            self._cached_dict = dsk
        return self._cached_dict

    def __getitem__(self, key):
        return self._dict[key]

    def __iter__(self):
        return iter(self._dict)

    def __len__(self):
        return len(self._dict)

    def is_materialized(self):
        return hasattr(self, "_cached_dict")

    def get_output_keys(self):
        return self.keys()  # FIXME! this implementation materializes the graph

    def _dask_keys(self):
        if self._cached_keys is not None:
            return self._cached_keys

        name, chunks, numblocks = self.name, self.chunks, self.numblocks

        def keys(*args):
            if not chunks:
                return [(name,)]
            ind = len(args)
            if ind + 1 == len(numblocks):
                result = [(name,) + args + (i,) for i in range(numblocks[ind])]
            else:
                result = [keys(*(args + (i,))) for i in range(numblocks[ind])]
            return result

        self._cached_keys = result = keys()
        return result

    def _construct_graph(self, deserializing=False):
        """Construct graph for a simple overlap operation."""
        axes = self.axes
        chunks = self.chunks
        name = self.name
        dask_keys = self._dask_keys()

        getitem_name = "getitem-" + self.token
        overlap_name = "overlap-" + self.token

        if deserializing:
            # Use CallableLazyImport objects to avoid importing dataframe
            # module on the scheduler
            concatenate3 = CallableLazyImport("dask.array.core.concatenate3")
        else:
            # Not running on distributed scheduler - Use explicit functions
            from dask.array.core import concatenate3

        dims = list(map(len, chunks))
        expand_key2 = functools.partial(
            _expand_keys_around_center, dims=dims, axes=axes
        )

        # Make keys for each of the surrounding sub-arrays
        interior_keys = toolz.pipe(
            dask_keys, flatten, map(expand_key2), map(flatten), toolz.concat, list
        )
        interior_slices = {}
        overlap_blocks = {}
        for k in interior_keys:
            frac_slice = fractional_slice((name,) + k, axes)
            if (name,) + k != frac_slice:
                interior_slices[(getitem_name,) + k] = frac_slice
            else:
                interior_slices[(getitem_name,) + k] = (name,) + k
                overlap_blocks[(overlap_name,) + k] = (
                    concatenate3,
                    (concrete, expand_key2((None,) + k, name=getitem_name)),
                )

        dsk = toolz.merge(interior_slices, overlap_blocks)
        return dsk


def _expand_keys_around_center(k, dims, name=None, axes=None):
    """Get all neighboring keys around center

    Parameters
    ----------
    k: tuple
        They key around which to generate new keys
    dims: Sequence[int]
        The number of chunks in each dimension
    name: Option[str]
        The name to include in the output keys, or none to include no name
    axes: Dict[int, int]
        The axes active in the expansion.  We don't expand on non-active axes

    Examples
    --------
    >>> _expand_keys_around_center(('x', 2, 3), dims=[5, 5], name='y', axes={0: 1, 1: 1})  # noqa: E501 # doctest: +NORMALIZE_WHITESPACE
    [[('y', 1.1, 2.1), ('y', 1.1, 3), ('y', 1.1, 3.9)],
     [('y',   2, 2.1), ('y',   2, 3), ('y',   2, 3.9)],
     [('y', 2.9, 2.1), ('y', 2.9, 3), ('y', 2.9, 3.9)]]

    >>> _expand_keys_around_center(('x', 0, 4), dims=[5, 5], name='y', axes={0: 1, 1: 1})  # noqa: E501 # doctest: +NORMALIZE_WHITESPACE
    [[('y',   0, 3.1), ('y',   0,   4)],
     [('y', 0.9, 3.1), ('y', 0.9,   4)]]
    """

    def inds(i, ind):
        rv = []
        if ind - 0.9 > 0:
            rv.append(ind - 0.9)
        rv.append(ind)
        if ind + 0.9 < dims[i] - 1:
            rv.append(ind + 0.9)
        return rv

    shape = []
    for i, ind in enumerate(k[1:]):
        num = 1
        if ind > 0:
            num += 1
        if ind < dims[i] - 1:
            num += 1
        shape.append(num)

    args = [
        inds(i, ind) if any((axes.get(i, 0),)) else [ind] for i, ind in enumerate(k[1:])
    ]
    if name is not None:
        args = [[name]] + args
    seq = list(product(*args))
    shape2 = [d if any((axes.get(i, 0),)) else 1 for i, d in enumerate(shape)]
    result = reshapelist(shape2, seq)
    return result


def reshapelist(shape, seq):
    """Reshape iterator to nested shape

    >>> reshapelist((2, 3), range(6))
    [[0, 1, 2], [3, 4, 5]]
    """
    if len(shape) == 1:
        return list(seq)
    else:
        n = int(len(seq) / shape[0])
        return [reshapelist(shape[1:], part) for part in toolz.partition(n, seq)]


def fractional_slice(task, axes):
    """

    >>> fractional_slice(('x', 5.1), {0: 2})
    (<built-in function getitem>, ('x', 5), (slice(-2, None, None),))

    >>> fractional_slice(('x', 3, 5.1), {0: 2, 1: 3})
    (<built-in function getitem>, ('x', 3, 5), (slice(None, None, None), slice(-3, None, None)))

    >>> fractional_slice(('x', 2.9, 5.1), {0: 2, 1: 3})
    (<built-in function getitem>, ('x', 3, 5), (slice(0, 2, None), slice(-3, None, None)))
    """
    rounded = (task[0],) + tuple(int(round(i)) for i in task[1:])

    index = []
    for i, (t, r) in enumerate(zip(task[1:], rounded[1:])):
        depth = axes.get(i, 0)
        if isinstance(depth, tuple):
            left_depth = depth[0]
            right_depth = depth[1]
        else:
            left_depth = depth
            right_depth = depth

        if t == r:
            index.append(slice(None, None, None))
        elif t < r and right_depth:
            index.append(slice(0, right_depth))
        elif t > r and left_depth:
            index.append(slice(-left_depth, None))
        else:
            index.append(slice(0, 0))
    index = tuple(index)

    if all(ind == slice(None, None, None) for ind in index):
        return task
    else:
        return (operator.getitem, rounded, index)


#
##
###  DataFrame Layers & Utilities
##
#


class SimpleShuffleLayer(Layer):
    """Simple HighLevelGraph Shuffle layer

    High-level graph layer for a simple shuffle operation in which
    each output partition depends on all input partitions.

    Parameters
    ----------
    name : str
        Name of new shuffled output collection.
    column : str or list of str
        Column(s) to be used to map rows to output partitions (by hashing).
    npartitions : int
        Number of output partitions.
    npartitions_input : int
        Number of partitions in the original (un-shuffled) DataFrame.
    ignore_index: bool, default False
        Ignore index during shuffle.  If ``True``, performance may improve,
        but index values will not be preserved.
    name_input : str
        Name of input collection.
    meta_input : pd.DataFrame-like object
        Empty metadata of input collection.
    parts_out : list of int (optional)
        List of required output-partition indices.
    annotations : dict (optional)
        Layer annotations
    """

    def __init__(
        self,
        name,
        column,
        npartitions,
        npartitions_input,
        ignore_index,
        name_input,
        meta_input,
        parts_out=None,
        annotations=None,
    ):
        self.name = name
        self.column = column
        self.npartitions = npartitions
        self.npartitions_input = npartitions_input
        self.ignore_index = ignore_index
        self.name_input = name_input
        self.meta_input = meta_input
        self.parts_out = parts_out or range(npartitions)
        self.split_name = "split-" + self.name

        # The scheduling policy of Dask is generally depth-first,
        # which works great in most cases. However, in case of shuffle,
        # it increases the memory usage significantly. This is because
        # depth-first delays the freeing of the result of `shuffle_group()`
        # until the end of the shuffling.
        #
        # We address this by manually setting a high "priority" to the
        # `getitem()` ("split") tasks, using annotations. This forces a
        # breadth-first scheduling of the tasks that directly depend on
        # the `shuffle_group()` output, allowing that data to be freed
        # much earlier.
        #
        # See https://github.com/dask/dask/pull/6051 for a detailed discussion.
        annotations = annotations or {}
        self._split_keys = None
        if "priority" not in annotations:
            annotations["priority"] = self._key_priority

        super().__init__(annotations=annotations)

    def _key_priority(self, key):
        assert isinstance(key, tuple)
        if key[0] == self.split_name:
            return 1
        else:
            return 0

    def get_output_keys(self):
        return {(self.name, part) for part in self.parts_out}

    def __repr__(self):
        return "SimpleShuffleLayer<name='{}', npartitions={}>".format(
            self.name, self.npartitions
        )

    def is_materialized(self):
        return hasattr(self, "_cached_dict")

    @property
    def _dict(self):
        """Materialize full dict representation"""
        if hasattr(self, "_cached_dict"):
            return self._cached_dict
        else:
            dsk = self._construct_graph()
            self._cached_dict = dsk
        return self._cached_dict

    def __getitem__(self, key):
        return self._dict[key]

    def __iter__(self):
        return iter(self._dict)

    def __len__(self):
        return len(self._dict)

    def _keys_to_parts(self, keys):
        """Simple utility to convert keys to partition indices."""
        parts = set()
        for key in keys:
            try:
                _name, _part = key
            except ValueError:
                continue
            if _name != self.name:
                continue
            parts.add(_part)
        return parts

    def _cull_dependencies(self, keys, parts_out=None):
        """Determine the necessary dependencies to produce `keys`.

        For a simple shuffle, output partitions always depend on
        all input partitions. This method does not require graph
        materialization.
        """
        deps = defaultdict(set)
        parts_out = parts_out or self._keys_to_parts(keys)
        for part in parts_out:
            deps[(self.name, part)] |= {
                (self.name_input, i) for i in range(self.npartitions_input)
            }
        return deps

    def _cull(self, parts_out):
        return SimpleShuffleLayer(
            self.name,
            self.column,
            self.npartitions,
            self.npartitions_input,
            self.ignore_index,
            self.name_input,
            self.meta_input,
            parts_out=parts_out,
        )

    def cull(self, keys, all_keys):
        """Cull a SimpleShuffleLayer HighLevelGraph layer.

        The underlying graph will only include the necessary
        tasks to produce the keys (indices) included in `parts_out`.
        Therefore, "culling" the layer only requires us to reset this
        parameter.
        """
        parts_out = self._keys_to_parts(keys)
        culled_deps = self._cull_dependencies(keys, parts_out=parts_out)
        if parts_out != set(self.parts_out):
            culled_layer = self._cull(parts_out)
            return culled_layer, culled_deps
        else:
            return self, culled_deps

    def _construct_graph(self, deserializing=False):
        """Construct graph for a simple shuffle operation."""

        shuffle_group_name = "group-" + self.name

        if deserializing:
            # Use CallableLazyImport objects to avoid importing dataframe
            # module on the scheduler
            concat_func = CallableLazyImport("dask.dataframe.core._concat")
            shuffle_group_func = CallableLazyImport(
                "dask.dataframe.shuffle.shuffle_group"
            )
        else:
            # Not running on distributed scheduler - Use explicit functions
            from dask.dataframe.core import _concat as concat_func
            from dask.dataframe.shuffle import shuffle_group as shuffle_group_func

        dsk = {}
        for part_out in self.parts_out:
            _concat_list = [
                (self.split_name, part_out, part_in)
                for part_in in range(self.npartitions_input)
            ]
            dsk[(self.name, part_out)] = (
                concat_func,
                _concat_list,
                self.ignore_index,
            )
            for _, _part_out, _part_in in _concat_list:
                dsk[(self.split_name, _part_out, _part_in)] = (
                    operator.getitem,
                    (shuffle_group_name, _part_in),
                    _part_out,
                )
                if (shuffle_group_name, _part_in) not in dsk:
                    dsk[(shuffle_group_name, _part_in)] = (
                        shuffle_group_func,
                        (self.name_input, _part_in),
                        self.column,
                        0,
                        self.npartitions,
                        self.npartitions,
                        self.ignore_index,
                        self.npartitions,
                    )

        return dsk


class ShuffleLayer(SimpleShuffleLayer):
    """Shuffle-stage HighLevelGraph layer

    High-level graph layer corresponding to a single stage of
    a multi-stage inter-partition shuffle operation.

    Stage: (shuffle-group) -> (shuffle-split) -> (shuffle-join)

    Parameters
    ----------
    name : str
        Name of new (partially) shuffled collection.
    column : str or list of str
        Column(s) to be used to map rows to output partitions (by hashing).
    inputs : list of tuples
        Each tuple dictates the data movement for a specific partition.
    stage : int
        Index of the current shuffle stage.
    npartitions : int
        Number of output partitions for the full (multi-stage) shuffle.
    npartitions_input : int
        Number of partitions in the original (un-shuffled) DataFrame.
    k : int
        A partition is split into this many groups during each stage.
    ignore_index: bool, default False
        Ignore index during shuffle.  If ``True``, performance may improve,
        but index values will not be preserved.
    name_input : str
        Name of input collection.
    meta_input : pd.DataFrame-like object
        Empty metadata of input collection.
    parts_out : list of int (optional)
        List of required output-partition indices.
    annotations : dict (optional)
        Layer annotations
    """

    def __init__(
        self,
        name,
        column,
        inputs,
        stage,
        npartitions,
        npartitions_input,
        nsplits,
        ignore_index,
        name_input,
        meta_input,
        parts_out=None,
        annotations=None,
    ):
        self.inputs = inputs
        self.stage = stage
        self.nsplits = nsplits
        super().__init__(
            name,
            column,
            npartitions,
            npartitions_input,
            ignore_index,
            name_input,
            meta_input,
            parts_out=parts_out or range(len(inputs)),
            annotations=annotations,
        )

    def __repr__(self):
        return "ShuffleLayer<name='{}', stage={}, nsplits={}, npartitions={}>".format(
            self.name, self.stage, self.nsplits, self.npartitions
        )

    def _cull_dependencies(self, keys, parts_out=None):
        """Determine the necessary dependencies to produce `keys`.

        Does not require graph materialization.
        """
        deps = defaultdict(set)
        parts_out = parts_out or self._keys_to_parts(keys)
        inp_part_map = {inp: i for i, inp in enumerate(self.inputs)}
        for part in parts_out:
            out = self.inputs[part]
            for k in range(self.nsplits):
                _inp = insert(out, self.stage, k)
                _part = inp_part_map[_inp]
                if self.stage == 0 and _part >= self.npartitions_input:
                    deps[(self.name, part)].add(("group-" + self.name, _inp, "empty"))
                else:
                    deps[(self.name, part)].add((self.name_input, _part))
        return deps

    def _cull(self, parts_out):
        return ShuffleLayer(
            self.name,
            self.column,
            self.inputs,
            self.stage,
            self.npartitions,
            self.npartitions_input,
            self.nsplits,
            self.ignore_index,
            self.name_input,
            self.meta_input,
            parts_out=parts_out,
        )

    def _construct_graph(self, deserializing=False):
        """Construct graph for a "rearrange-by-column" stage."""

        shuffle_group_name = "group-" + self.name

        if deserializing:
            # Use CallableLazyImport objects to avoid importing dataframe
            # module on the scheduler
            concat_func = CallableLazyImport("dask.dataframe.core._concat")
            shuffle_group_func = CallableLazyImport(
                "dask.dataframe.shuffle.shuffle_group"
            )
        else:
            # Not running on distributed scheduler - Use explicit functions
            from dask.dataframe.core import _concat as concat_func
            from dask.dataframe.shuffle import shuffle_group as shuffle_group_func

        dsk = {}
        inp_part_map = {inp: i for i, inp in enumerate(self.inputs)}
        for part in self.parts_out:
            out = self.inputs[part]

            _concat_list = []  # get_item tasks to concat for this output partition
            for i in range(self.nsplits):
                # Get out each individual dataframe piece from the dicts
                _inp = insert(out, self.stage, i)
                _idx = out[self.stage]
                _concat_list.append((self.split_name, _idx, _inp))

            # concatenate those pieces together, with their friends
            dsk[(self.name, part)] = (
                concat_func,
                _concat_list,
                self.ignore_index,
            )

            for _, _idx, _inp in _concat_list:
                dsk[(self.split_name, _idx, _inp)] = (
                    operator.getitem,
                    (shuffle_group_name, _inp),
                    _idx,
                )

                if (shuffle_group_name, _inp) not in dsk:
                    # Initial partitions (output of previous stage)
                    _part = inp_part_map[_inp]
                    if self.stage == 0:
                        if _part < self.npartitions_input:
                            input_key = (self.name_input, _part)
                        else:
                            # In order to make sure that to_serialize() serialize the
                            # empty dataframe input, we add it as a key.
                            input_key = (shuffle_group_name, _inp, "empty")
                            dsk[input_key] = self.meta_input
                    else:
                        input_key = (self.name_input, _part)

                    # Convert partition into dict of dataframe pieces
                    dsk[(shuffle_group_name, _inp)] = (
                        shuffle_group_func,
                        input_key,
                        self.column,
                        self.stage,
                        self.nsplits,
                        self.npartitions_input,
                        self.ignore_index,
                        self.npartitions,
                    )

        return dsk


class BroadcastJoinLayer(Layer):
    """Broadcast-based Join Layer

    High-level graph layer for a join operation requiring the
    smaller collection to be broadcasted to every partition of
    the larger collection.

    Parameters
    ----------
    name : str
        Name of new (joined) output collection.
    lhs_name: string
        "Left" DataFrame collection to join.
    lhs_npartitions: int
        Number of partitions in "left" DataFrame collection.
    rhs_name: string
        "Right" DataFrame collection to join.
    rhs_npartitions: int
        Number of partitions in "right" DataFrame collection.
    parts_out : list of int (optional)
        List of required output-partition indices.
    annotations : dict (optional)
        Layer annotations.
    **merge_kwargs : **dict
        Keyword arguments to be passed to chunkwise merge func.
    """

    def __init__(
        self,
        name,
        npartitions,
        lhs_name,
        lhs_npartitions,
        rhs_name,
        rhs_npartitions,
        parts_out=None,
        annotations=None,
        left_on=None,
        right_on=None,
        **merge_kwargs,
    ):
        super().__init__(annotations=annotations)
        self.name = name
        self.npartitions = npartitions
        self.lhs_name = lhs_name
        self.lhs_npartitions = lhs_npartitions
        self.rhs_name = rhs_name
        self.rhs_npartitions = rhs_npartitions
        self.parts_out = parts_out or set(range(self.npartitions))
        self.left_on = tuple(left_on) if isinstance(left_on, list) else left_on
        self.right_on = tuple(right_on) if isinstance(right_on, list) else right_on
        self.merge_kwargs = merge_kwargs
        self.how = self.merge_kwargs.get("how")
        self.merge_kwargs["left_on"] = self.left_on
        self.merge_kwargs["right_on"] = self.right_on

    def get_output_keys(self):
        return {(self.name, part) for part in self.parts_out}

    def __repr__(self):
        return "BroadcastJoinLayer<name='{}', how={}, lhs={}, rhs={}>".format(
            self.name, self.how, self.lhs_name, self.rhs_name
        )

    def is_materialized(self):
        return hasattr(self, "_cached_dict")

    @property
    def _dict(self):
        """Materialize full dict representation"""
        if hasattr(self, "_cached_dict"):
            return self._cached_dict
        else:
            dsk = self._construct_graph()
            self._cached_dict = dsk
        return self._cached_dict

    def __getitem__(self, key):
        return self._dict[key]

    def __iter__(self):
        return iter(self._dict)

    def __len__(self):
        return len(self._dict)

    def _keys_to_parts(self, keys):
        """Simple utility to convert keys to partition indices."""
        parts = set()
        for key in keys:
            try:
                _name, _part = key
            except ValueError:
                continue
            if _name != self.name:
                continue
            parts.add(_part)
        return parts

    @property
    def _broadcast_plan(self):
        # Return structure (tuple):
        # (
        #     <broadcasted-collection-name>,
        #     <broadcasted-collection-npartitions>,
        #     <other-collection-npartitions>,
        #     <other-collection-on>,
        # )
        if self.lhs_npartitions < self.rhs_npartitions:
            # Broadcasting the left
            return (
                self.lhs_name,
                self.lhs_npartitions,
                self.rhs_name,
                self.right_on,
            )
        else:
            # Broadcasting the right
            return (
                self.rhs_name,
                self.rhs_npartitions,
                self.lhs_name,
                self.left_on,
            )

    def _cull_dependencies(self, keys, parts_out=None):
        """Determine the necessary dependencies to produce `keys`.

        For a broadcast join, output partitions always depend on
        all partitions of the broadcasted collection, but only one
        partition of the "other" collection.
        """
        # Get broadcast info
        bcast_name, bcast_size, other_name = self._broadcast_plan[:3]

        deps = defaultdict(set)
        parts_out = parts_out or self._keys_to_parts(keys)
        for part in parts_out:
            deps[(self.name, part)] |= {(bcast_name, i) for i in range(bcast_size)}
            deps[(self.name, part)] |= {
                (other_name, part),
            }
        return deps

    def _cull(self, parts_out):
        return BroadcastJoinLayer(
            self.name,
            self.npartitions,
            self.lhs_name,
            self.lhs_npartitions,
            self.rhs_name,
            self.rhs_npartitions,
            annotations=self.annotations,
            parts_out=parts_out,
            **self.merge_kwargs,
        )

    def cull(self, keys, all_keys):
        """Cull a BroadcastJoinLayer HighLevelGraph layer.

        The underlying graph will only include the necessary
        tasks to produce the keys (indices) included in `parts_out`.
        Therefore, "culling" the layer only requires us to reset this
        parameter.
        """
        parts_out = self._keys_to_parts(keys)
        culled_deps = self._cull_dependencies(keys, parts_out=parts_out)
        if parts_out != set(self.parts_out):
            culled_layer = self._cull(parts_out)
            return culled_layer, culled_deps
        else:
            return self, culled_deps

    def _construct_graph(self, deserializing=False):
        """Construct graph for a broadcast join operation."""

        inter_name = "inter-" + self.name
        split_name = "split-" + self.name

        if deserializing:
            # Use CallableLazyImport objects to avoid importing dataframe
            # module on the scheduler
            split_partition_func = CallableLazyImport(
                "dask.dataframe.multi._split_partition"
            )
            concat_func = CallableLazyImport("dask.dataframe.multi._concat_wrapper")
            merge_chunk_func = CallableLazyImport(
                "dask.dataframe.multi._merge_chunk_wrapper"
            )
        else:
            # Not running on distributed scheduler - Use explicit functions
            from dask.dataframe.multi import _concat_wrapper as concat_func
            from dask.dataframe.multi import _merge_chunk_wrapper as merge_chunk_func
            from dask.dataframe.multi import _split_partition as split_partition_func

        # Get broadcast "plan"
        bcast_name, bcast_size, other_name, other_on = self._broadcast_plan
        bcast_side = "left" if self.lhs_npartitions < self.rhs_npartitions else "right"

        # Loop over output partitions, which should be a 1:1
        # mapping with the input partitions of "other".
        # Culling should allow us to avoid generating tasks for
        # any output partitions that are not requested (via `parts_out`)
        dsk = {}
        for i in self.parts_out:
            # Split each "other" partition by hash
            if self.how != "inner":
                dsk[(split_name, i)] = (
                    split_partition_func,
                    (other_name, i),
                    other_on,
                    bcast_size,
                )

            # For each partition of "other", we need to join
            # to each partition of "bcast". If it is a "left"
            # or "right" join, there should be a unique mapping
            # between the local splits of "other" and the
            # partitions of "bcast" (which means we need an
            # additional `getitem` operation to isolate the
            # correct split of each "other" partition).
            _concat_list = []
            for j in range(bcast_size):
                # Specify arg list for `merge_chunk`
                _merge_args = [
                    (
                        operator.getitem,
                        (split_name, i),
                        j,
                    )
                    if self.how != "inner"
                    else (other_name, i),
                    (bcast_name, j),
                ]
                if bcast_side == "left":
                    # If the left is broadcasted, the
                    # arg list needs to be reversed
                    _merge_args.reverse()
                inter_key = (inter_name, i, j)
                dsk[inter_key] = (
                    apply,
                    merge_chunk_func,
                    _merge_args,
                    self.merge_kwargs,
                )
                _concat_list.append(inter_key)

            # Concatenate the merged results for each output partition
            dsk[(self.name, i)] = (concat_func, _concat_list)

        return dsk


class DataFrameIOLayer(Blockwise):
    """DataFrame-based Blockwise Layer with IO

    Parameters
    ----------
    name : str
        Name to use for the constructed layer.
    columns : str, list or None
        Field name(s) to read in as columns in the output.
    inputs : list or BlockwiseDep
        List of arguments to be passed to ``io_func`` so
        that the materialized task to produce partition ``i``
        will be: ``(<io_func>, inputs[i])``.  Note that each
        element of ``inputs`` is typically a tuple of arguments.
    io_func : callable
        A callable function that takes in a single tuple
        of arguments, and outputs a DataFrame partition.
        Column projection will be supported for functions
        that satisfy the ``DataFrameIOFunction`` protocol.
    label : str (optional)
        String to use as a prefix in the place-holder collection
        name. If nothing is specified (default), "subset-" will
        be used.
    produces_tasks : bool (optional)
        Whether one or more elements of `inputs` is expected to
        contain a nested task. This argument in only used for
        serialization purposes, and will be deprecated in the
        future. Default is False.
    creation_info: dict (optional)
        Dictionary containing the callable function ('func'),
        positional arguments ('args'), and key-word arguments
        ('kwargs') used to produce the dask collection with
        this underlying ``DataFrameIOLayer``.
    annotations: dict (optional)
        Layer annotations to pass through to Blockwise.
    """

    def __init__(
        self,
        name,
        columns,
        inputs,
        io_func,
        label=None,
        produces_tasks=False,
        creation_info=None,
        annotations=None,
    ):
        self.name = name
        self._columns = columns
        self.inputs = inputs
        self.io_func = io_func
        self.label = label
        self.produces_tasks = produces_tasks
        self.annotations = annotations
        self.creation_info = creation_info

        if not isinstance(inputs, BlockwiseDep):
            # Define mapping between key index and "part"
            io_arg_map = BlockwiseDepDict(
                {(i,): inp for i, inp in enumerate(self.inputs)},
                produces_tasks=self.produces_tasks,
            )
        else:
            io_arg_map = inputs

        # Use Blockwise initializer
        dsk = {self.name: (io_func, blockwise_token(0))}
        super().__init__(
            output=self.name,
            output_indices="i",
            dsk=dsk,
            indices=[(io_arg_map, "i")],
            numblocks={},
            annotations=annotations,
        )

    @property
    def columns(self):
        """Current column projection for this layer"""
        return self._columns

    def project_columns(self, columns):
        """Produce a column projection for this IO layer.
        Given a list of required output columns, this method
        returns the projected layer.
        """
        from dask.dataframe.io.utils import DataFrameIOFunction

        columns = list(columns)

        if self.columns is None or set(self.columns).issuperset(columns):
            # Apply column projection in IO function.
            # Must satisfy `DataFrameIOFunction` protocol
            if isinstance(self.io_func, DataFrameIOFunction):
                io_func = self.io_func.project_columns(columns)
            else:
                io_func = self.io_func

            layer = DataFrameIOLayer(
                (self.label or "subset") + "-" + tokenize(self.name, columns),
                columns,
                self.inputs,
                io_func,
                label=self.label,
                produces_tasks=self.produces_tasks,
                annotations=self.annotations,
            )
            return layer
        else:
            # Default behavior
            return self

    def __repr__(self):
        return "DataFrameIOLayer<name='{}', n_parts={}, columns={}>".format(
            self.name, len(self.inputs), self.columns
        )


class DataFrameTreeReduction(Layer):
    """DataFrame Tree-Reduction Layer

    Parameters
    ----------
    name : str
        Name to use for the constructed layer.
    name_input : str
        Name of the input layer that is being reduced.
    npartitions_input : str
        Number of partitions in the input layer.
    concat_func : callable
        Function used by each tree node to reduce a list of inputs
        into a single output value. This function must accept only
        a list as its first positional argument.
    tree_node_func : callable
        Function used on the output of ``concat_func`` in each tree
        node. This function must accept the output of ``concat_func``
        as its first positional argument.
    finalize_func : callable, optional
        Function used in place of ``tree_node_func`` on the final tree
        node(s) to produce the final output for each split. By default,
        ``tree_node_func`` will be used.
    split_every : int, optional
        This argument specifies the maximum number of input nodes
        to be handled by any one task in the tree. Defaults to 32.
    split_out : int, optional
        This argument specifies the number of output nodes in the
        reduction tree. If ``split_out`` is set to an integer >=1, the
        input tasks must contain data that can be indexed by a ``getitem``
        operation with a key in the range ``[0, split_out)``.
    output_partitions : list, optional
        List of required output partitions. This parameter is used
        internally by Dask for high-level culling.
    tree_node_name : str, optional
        Name to use for intermediate tree-node tasks.
    """

    name: str
    name_input: str
    npartitions_input: int
    concat_func: Callable
    tree_node_func: Callable
    finalize_func: Callable | None
    split_every: int
    split_out: int
    output_partitions: list[int]
    tree_node_name: str
    widths: list[int]
    height: int

    def __init__(
        self,
        name: str,
        name_input: str,
        npartitions_input: int,
        concat_func: Callable,
        tree_node_func: Callable,
        finalize_func: Callable | None = None,
        split_every: int = 32,
        split_out: int | None = None,
        output_partitions: list[int] | None = None,
        tree_node_name: str | None = None,
        annotations: dict[str, Any] | None = None,
    ):
        super().__init__(annotations=annotations)
        self.name = name
        self.name_input = name_input
        self.npartitions_input = npartitions_input
        self.concat_func = concat_func
        self.tree_node_func = tree_node_func
        self.finalize_func = finalize_func
        self.split_every = split_every
        self.split_out = split_out  # type: ignore
        self.output_partitions = (
            list(range(self.split_out or 1))
            if output_partitions is None
            else output_partitions
        )
        self.tree_node_name = tree_node_name or "tree_node-" + self.name

        # Calculate tree widths and height
        # (Used to get output keys without materializing)
        parts = self.npartitions_input
        self.widths = [parts]
        while parts > 1:
            parts = math.ceil(parts / self.split_every)
            self.widths.append(int(parts))
        self.height = len(self.widths)

    def _make_key(self, *name_parts, split=0):
        # Helper function construct a key
        # with a "split" element when
        # bool(split_out) is True
        return name_parts + (split,) if self.split_out else name_parts

    def _define_task(self, input_keys, final_task=False):
        # Define nested concatenation and func task
        if final_task and self.finalize_func:
            outer_func = self.finalize_func
        else:
            outer_func = self.tree_node_func
        return (toolz.pipe, input_keys, self.concat_func, outer_func)

    def _construct_graph(self):
        """Construct graph for a tree reduction."""

        dsk = {}
        if not self.output_partitions:
            return dsk

        # Deal with `bool(split_out) == True`.
        # These cases require that the input tasks
        # return a type that enables getitem operation
        # with indices: [0, split_out)
        # Therefore, we must add "getitem" tasks to
        # select the appropriate element for each split
        name_input_use = self.name_input
        if self.split_out:
            name_input_use += "-split"
            for s in self.output_partitions:
                for p in range(self.npartitions_input):
                    dsk[self._make_key(name_input_use, p, split=s)] = (
                        operator.getitem,
                        (self.name_input, p),
                        s,
                    )

        if self.height >= 2:
            # Loop over output splits
            for s in self.output_partitions:
                # Loop over reduction levels
                for depth in range(1, self.height):
                    # Loop over reduction groups
                    for group in range(self.widths[depth]):
                        # Calculate inputs for the current group
                        p_max = self.widths[depth - 1]
                        lstart = self.split_every * group
                        lstop = min(lstart + self.split_every, p_max)
                        if depth == 1:
                            # Input nodes are from input layer
                            input_keys = [
                                self._make_key(name_input_use, p, split=s)
                                for p in range(lstart, lstop)
                            ]
                        else:
                            # Input nodes are tree-reduction nodes
                            input_keys = [
                                self._make_key(
                                    self.tree_node_name, p, depth - 1, split=s
                                )
                                for p in range(lstart, lstop)
                            ]

                        # Define task
                        if depth == self.height - 1:
                            # Final Node (Use fused `self.tree_finalize` task)
                            assert (
                                group == 0
                            ), f"group = {group}, not 0 for final tree reduction task"
                            dsk[(self.name, s)] = self._define_task(
                                input_keys, final_task=True
                            )
                        else:
                            # Intermediate Node
                            dsk[
                                self._make_key(
                                    self.tree_node_name, group, depth, split=s
                                )
                            ] = self._define_task(input_keys, final_task=False)
        else:
            # Deal with single-partition case
            for s in self.output_partitions:
                input_keys = [self._make_key(name_input_use, 0, split=s)]
                dsk[(self.name, s)] = self._define_task(input_keys, final_task=True)

        return dsk

    def __repr__(self):
        return "DataFrameTreeReduction<name='{}', input_name={}, split_out={}>".format(
            self.name, self.name_input, self.split_out
        )

    def _output_keys(self):
        return {(self.name, s) for s in self.output_partitions}

    def get_output_keys(self):
        if hasattr(self, "_cached_output_keys"):
            return self._cached_output_keys
        else:
            output_keys = self._output_keys()
            self._cached_output_keys = output_keys
        return self._cached_output_keys

    def is_materialized(self):
        return hasattr(self, "_cached_dict")

    @property
    def _dict(self):
        """Materialize full dict representation"""
        if hasattr(self, "_cached_dict"):
            return self._cached_dict
        else:
            dsk = self._construct_graph()
            self._cached_dict = dsk
        return self._cached_dict

    def __getitem__(self, key):
        return self._dict[key]

    def __iter__(self):
        return iter(self._dict)

    def __len__(self):
        # Start with "base" tree-reduction size
        tree_size = (sum(self.widths[1:]) or 1) * (self.split_out or 1)
        if self.split_out:
            # Add on "split-*" tasks used for `getitem` ops
            return tree_size + self.npartitions_input * len(self.output_partitions)
        return tree_size

    def _keys_to_output_partitions(self, keys):
        """Simple utility to convert keys to output partition indices."""
        splits = set()
        for key in keys:
            try:
                _name, _split = key
            except ValueError:
                continue
            if _name != self.name:
                continue
            splits.add(_split)
        return splits

    def _cull(self, output_partitions):
        return DataFrameTreeReduction(
            self.name,
            self.name_input,
            self.npartitions_input,
            self.concat_func,
            self.tree_node_func,
            finalize_func=self.finalize_func,
            split_every=self.split_every,
            split_out=self.split_out,
            output_partitions=output_partitions,
            tree_node_name=self.tree_node_name,
            annotations=self.annotations,
        )

    def cull(self, keys, all_keys):
        """Cull a DataFrameTreeReduction HighLevelGraph layer"""
        deps = {
            (self.name, 0): {
                (self.name_input, i) for i in range(self.npartitions_input)
            }
        }
        output_partitions = self._keys_to_output_partitions(keys)
        if output_partitions != set(self.output_partitions):
            culled_layer = self._cull(output_partitions)
            return culled_layer, deps
        else:
            return self, deps
