"""Utils for the python server."""
import itertools
from typing import Any, Callable, Generator, Iterable, Iterator, TypeVar, Union, cast

from .schema import Item
from .utils import chunks, is_primitive


def _deep_flatten(input: Union[Iterator, object],
                  is_primitive_predicate: Callable[[object], bool]) -> Generator:
  """Flattens a nested iterable."""
  if is_primitive_predicate(input):
    yield input
  elif isinstance(input, dict):
    yield input
  elif is_primitive(input):
    yield input
  else:
    for elem in cast(Iterator, input):
      yield from _deep_flatten(elem, is_primitive_predicate)


def deep_flatten(input: Union[Iterator, Iterable],
                 is_primitive_predicate: Callable[[object], bool] = is_primitive) -> Iterator:
  """Flattens a deeply nested iterator.

  Primitives and dictionaries are not flattened. The user can also provide a predicate to determine
  what is a primitive.
  """
  return _deep_flatten(input, is_primitive_predicate)


def _deep_unflatten(flat_input: Iterator[list[object]], original_input: Union[Iterable, object],
                    is_primitive_predicate: Callable[[object], bool]) -> Union[list, dict]:
  """Unflattens a deeply flattened iterable according to the original iterable's structure."""
  if is_primitive_predicate(original_input):
    return next(flat_input)
  else:
    values: Iterable
    if isinstance(original_input, dict):
      values = original_input.values()
    else:
      values = cast(Iterable, original_input)
    return [_deep_unflatten(flat_input, orig_elem, is_primitive_predicate) for orig_elem in values]


def deep_unflatten(flat_input: Union[Iterable, Iterator],
                   original_input: Union[Iterable, object],
                   is_primitive_predicate: Callable[[object], bool] = is_primitive) -> list:
  """Unflattens a deeply flattened iterable according to the original iterable's structure."""
  return cast(list, _deep_unflatten(iter(flat_input), original_input, is_primitive_predicate))


TFlatten = TypeVar('TFlatten')


def flatten(inputs: Iterable[Iterable[TFlatten]]) -> Iterator[TFlatten]:
  """Flattens a nested iterator.

  Only supports flattening one level deep.
  """
  for input in inputs:
    yield from input


TUnflatten = TypeVar('TUnflatten')


def unflatten(flat_inputs: Union[Iterable[TUnflatten], Iterator[TUnflatten]],
              original_inputs: Iterable[Iterable[Any]]) -> Iterator[list[TUnflatten]]:
  """Unflattens a flattened iterable according to the original iterable's structure."""
  flat_inputs_iter = iter(flat_inputs)
  for original_input in original_inputs:
    yield [next(flat_inputs_iter) for _ in original_input]


TFlatBatchedInput = TypeVar('TFlatBatchedInput')
TFlatBatchedOutput = TypeVar('TFlatBatchedOutput')


def flat_batched_compute(input: Iterable[Iterable[TFlatBatchedInput]],
                         f: Callable[[list[TFlatBatchedInput]], Iterable[TFlatBatchedOutput]],
                         batch_size: int) -> Iterable[Iterable[TFlatBatchedOutput]]:
  """Flatten the input, batched call f, and return the output unflattened."""
  # Tee the input so we can use it twice for the input and output shapes.
  input_1, input_2 = itertools.tee(input, 2)
  batches = chunks(flatten(input_1), batch_size)
  batched_outputs = flatten((f(batch) for batch in batches))
  return unflatten(batched_outputs, input_2)


TBatchSpanVectorOutput = TypeVar('TBatchSpanVectorOutput', bound=Item)