from abc import ABC, abstractmethod
from pandas import DataFrame, Series
from pandas.api.types import is_numeric_dtype
from typing import Any, Union

class MVStrategy(ABC):
    """A way to handle missing values in a dataframe."""

    @abstractmethod
    def apply(self, df: DataFrame, label: str, series: Series) -> DataFrame:
        """Apply the current strategy to the given series.

        The series is described by its label and dataframe."""
        return df

    @staticmethod
    def list_available(series: Series) -> list['MVStrategy']:
        """Get all the strategies that can be used."""
        choices = [DropStrategy(), ModeStrategy()]
        if is_numeric_dtype(series):
            choices.extend((MeanStrategy(), MedianStrategy()))
        return choices


class DropStrategy(MVStrategy):
    #@typing.override
    def apply(self, df: DataFrame, label: str, series: Series) -> DataFrame:
        df.dropna(subset=label, inplace=True)
        return df

    def __str__(self) -> str:
        return "Drop"


class PositionStrategy(MVStrategy):
    #@typing.override
    def apply(self, df: DataFrame, label: str, series: Series) -> DataFrame:
        series.fillna(self.get_value(series), inplace=True)
        return df

    @abstractmethod
    def get_value(self, series: Series) -> Any:
        pass


class MeanStrategy(PositionStrategy):
    #@typing.override
    def get_value(self, series: Series) -> Union[int, float]:
        return series.mean()

    def __str__(self) -> str:
        return "Use mean"


class MedianStrategy(PositionStrategy):
    #@typing.override
    def get_value(self, series: Series) -> Union[int, float]:
        return series.median()

    def __str__(self) -> str:
        return "Use median"


class ModeStrategy(PositionStrategy):
    #@typing.override
    def get_value(self, series: Series) -> Any:
        return series.mode()[0]

    def __str__(self) -> str:
        return "Use mode"