import pandas as pd


def add_time_features(df: pd.DataFrame, timestamp_col: str = "timestamp") -> pd.DataFrame:
    result = df.copy()

    if timestamp_col not in result.columns:
        return result

    result[timestamp_col] = pd.to_datetime(result[timestamp_col])

    result["hour"] = result[timestamp_col].dt.hour
    result["day_of_week"] = result[timestamp_col].dt.dayofweek
    result["day_of_month"] = result[timestamp_col].dt.day
    result["month"] = result[timestamp_col].dt.month

    result["hour_sin"] = _sin_encode(result["hour"], 24)
    result["hour_cos"] = _cos_encode(result["hour"], 24)
    result["day_sin"] = _sin_encode(result["day_of_week"], 7)
    result["day_cos"] = _cos_encode(result["day_of_week"], 7)

    return result


def _sin_encode(x, period):
    import numpy as np
    return np.sin(2 * np.pi * x / period)


def _cos_encode(x, period):
    import numpy as np
    return np.cos(2 * np.pi * x / period)


__all__ = ["add_time_features"]