import datetime as dt
from typing import List, Optional

import pandas as pd


__all__ = ["interpolate_series"]


def interpolate_series(
    start_date: dt.datetime,
    end_date: dt.datetime,
    dates: List[dt.datetime],
    values: List[int],
    historical_date: Optional[dt.datetime] = None,
    historical_value: Optional[int] = None,
) -> List[int]:
    series = pd.Series(data=values, index=pd.DatetimeIndex(dates))

    if dates[0] > start_date and historical_date is not None and historical_value is not None:
        # if there is something to fill at tail, and we have historical value
        interpolation_start_date = historical_date
        historical_series = pd.Series(data=(historical_value,), index=pd.DatetimeIndex((historical_date,)))
        series = pd.concat((historical_series, series))
    else:
        interpolation_start_date = dates[0]

    series = series.reindex(pd.date_range(interpolation_start_date, end_date, freq="D"))

    # fill head with last known value
    series = series.interpolate(method="ffill", limit_area="outside")
    # interpolate everything else
    series = series.interpolate(method="time", limit_area="inside")
    # take only integer part
    series = series.astype("ulonglong")
    # Take only dates in the range
    # https://github.com/python/mypy/issues/2410
    series = series[start_date:]  # type: ignore

    return series.tolist()