from typing import Iterator, List

from pts.dataset import DataEntry, Dataset
from .transform import Chain, Transformation


class TransformedDataset(Dataset):
    """
    A dataset that corresponds to applying a list of transformations to each
    element in the base_dataset.
    This only supports SimpleTransformations, which do the same thing at
    prediction and training time.


    Parameters
    ----------
    base_dataset
        Dataset to transform
    transformations
        List of transformations to apply
    """

    def __init__(
        self, base_dataset: Dataset, transformations: List[Transformation]
    ) -> None:
        self.base_dataset = base_dataset
        self.transformations = Chain(transformations)

    def __iter__(self) -> Iterator[DataEntry]:
        yield from self.transformations(self.base_dataset, is_train=True)

    def __len__(self):
        return sum(1 for _ in self)