from abc import ABC, abstractmethod
from typing import Callable, Iterator, List
from functools import reduce


from pts.dataset import DataEntry


MAX_IDLE_TRANSFORMS = 100


class Transformation(ABC):
    @abstractmethod
    def __call__(
        self, data_it: Iterator[DataEntry], is_train: bool
    ) -> Iterator[DataEntry]:
        pass

    def estimate(self, data_it: Iterator[DataEntry]) -> Iterator[DataEntry]:
        return data_it  # default is to pass through without estimation

    def chain(self, other: "Transformation") -> "Chain":
        return Chain(self, other)

    def __add__(self, other: "Transformation") -> "Chain":
        return self.chain(other)


class Chain(Transformation):
    """
    Chain multiple transformations together.
    """

    def __init__(self, trans: List[Transformation]) -> None:
        self.transformations = []
        for transformation in trans:
            # flatten chains
            if isinstance(transformation, Chain):
                self.transformations.extend(transformation.transformations)
            else:
                self.transformations.append(transformation)

    def __call__(
        self, data_it: Iterator[DataEntry], is_train: bool
    ) -> Iterator[DataEntry]:
        tmp = data_it
        for t in self.transformations:
            tmp = t(tmp, is_train)
        return tmp

    def estimate(self, data_it: Iterator[DataEntry]) -> Iterator[DataEntry]:
        return reduce(lambda x, y: y.estimate(x), self.transformations, data_it)


class Identity(Transformation):
    def __call__(
        self, data_it: Iterator[DataEntry], is_train: bool
    ) -> Iterator[DataEntry]:
        return data_it


class MapTransformation(Transformation):
    """
    Base class for Transformations that returns exactly one result per input in the stream.
    """

    def __call__(self, data_it: Iterator[DataEntry], is_train: bool) -> Iterator:
        for data_entry in data_it:
            try:
                yield self.map_transform(data_entry.copy(), is_train)
            except Exception as e:
                raise e

    @abstractmethod
    def map_transform(self, data: DataEntry, is_train: bool) -> DataEntry:
        pass


class SimpleTransformation(MapTransformation):
    """
    Element wise transformations that are the same in train and test mode
    """

    def map_transform(self, data: DataEntry, is_train: bool) -> DataEntry:
        return self.transform(data)

    @abstractmethod
    def transform(self, data: DataEntry) -> DataEntry:
        pass


class AdhocTransform(SimpleTransformation):
    """
    Applies a function as a transformation
    This is called ad-hoc, because it is not serializable.
    It is OK to use this for experiments and outside of a model pipeline that
    needs to be serialized.
    """

    def __init__(self, func: Callable[[DataEntry], DataEntry]) -> None:
        self.func = func

    def transform(self, data: DataEntry) -> DataEntry:
        return self.func(data.copy())


class FlatMapTransformation(Transformation):
    """
    Transformations that yield zero or more results per input, but do not combine
    elements from the input stream.
    """

    def __call__(self, data_it: Iterator[DataEntry], is_train: bool) -> Iterator:
        num_idle_transforms = 0
        for data_entry in data_it:
            num_idle_transforms += 1
            try:
                for result in self.flatmap_transform(data_entry.copy(), is_train):
                    num_idle_transforms = 0
                    yield result
            except Exception as e:
                raise e
            if num_idle_transforms > MAX_IDLE_TRANSFORMS:
                raise Exception(
                    f"Reached maximum number of idle transformation calls.\n"
                    f"This means the transformation looped over "
                    f"MAX_IDLE_TRANSFORMS={MAX_IDLE_TRANSFORMS} "
                    f"inputs without returning any output.\n"
                    f"This occurred in the following transformation:\n{self}"
                )

    @abstractmethod
    def flatmap_transform(self, data: DataEntry, is_train: bool) -> Iterator[DataEntry]:
        pass


class FilterTransformation(FlatMapTransformation):
    def __init__(self, condition: Callable[[DataEntry], bool]) -> None:
        self.condition = condition

    def flatmap_transform(self, data: DataEntry, is_train: bool) -> Iterator[DataEntry]:
        if self.condition(data):
            yield data