"""Map 100m grid_id (r{row}_c{col}) → Wuhan district name."""
from functools import lru_cache

import pandas as pd

from config import PROJECT_ROOT


@lru_cache(maxsize=1)
def grid_district_lookup() -> dict[str, str]:
    """Loaded once from processed/grid_district_mapping.parquet."""
    path = PROJECT_ROOT / "processed" / "grid_district_mapping.parquet"
    if not path.exists():
        return {}
    df = pd.read_parquet(path)
    df = df.dropna(subset=["district_name"])
    return dict(zip(df["grid_id"].astype(str), df["district_name"].astype(str)))


def district_for_grid(grid_id: str, default: str = "其他") -> str:
    return grid_district_lookup().get(grid_id, default)