import polars as pl
import pandas as pd
from typing import Union, Optional, List
import io

def shelter_adequacy_analysis(
    data: Union[str, pd.DataFrame, pl.DataFrame, io.BytesIO],
    condition_col: str,
    occupancy_col: Optional[str] = None
) -> pl.DataFrame:
    """
    Shelter Adequacy Analysis
    =========================

    What
    ----
    Assess shelter condition/overcrowding.

    When
    ----
    Shelter needs assessments.

    Why
    ---
    Identify inadequate housing for targeting.

    Parameters
    ----------
    data : str | pd.DataFrame | pl.DataFrame | io.BytesIO
        Input dataset.
    condition_col : str
        Column describing condition (e.g., good/average/poor).
    occupancy_col : str | None
        Optional occupancy or persons per room.

    Returns
    -------
    pl.DataFrame
        Placeholder adequacy flags/scores.
    """
    if isinstance(data, str):
        df = pl.read_csv(data)
    elif isinstance(data, io.BytesIO):
        df = pl.read_csv(data)
    elif isinstance(data, pd.DataFrame):
        df = pl.from_pandas(data)
    elif isinstance(data, pl.DataFrame):
        df = data
    else:
        raise TypeError("Unsupported data type")
    return df.with_columns(pl.lit(0.0).alias("shelter_adequacy_score_placeholder"))
