from sklearn.linear_model import LinearRegression


def parse_regression_coef_to_array(
    model: LinearRegression,
    poly_features: list[str],
    array_name: str,
    rows: list[str] = [],
) -> list[str]:
    """Convenient function to parse the model coefficients into a cpp code string.

    Args:
        model (LinearRegression): A fitted linear regression model.
        poly_features (list[str]): A list with the names of the polynomial features.
        array_name (str): The name of the created cpp array.
        rows (list[str], optional): In case of a matrix, list of rows. Defaults to [].

    Returns:
        list[str]: List of strings, first entry is the comment, second the cpp code.
    """
    intercept = model.intercept_ != 0.0
    indices = [i for i in range(len(poly_features)) if model.coef_[i] != 0.0]
    feature_comment = (
        ("// param[0] + " if intercept else "// ")
        + " + ".join(
            [
                f"param[{idx}]*{poly_features[param_index]}"
                for idx, param_index in enumerate(indices, start=intercept)
            ],
        )
        + "\n"
    )
    n_col = sum(model.coef_ != 0.0) + model.fit_intercept
    if not rows:
        cpp_decl = f"static constexpr std::array<float, {n_col}> {array_name}"
        cpp_decl += (
            "{"
            + (str(model.intercept_) + "f," if intercept else "")
            + ",".join([str(coef) + "f" for coef in model.coef_ if coef != 0.0])
            + "};\n"
        )
        return [feature_comment, cpp_decl]
    else:
        n_row = len(rows)
        cpp_decl = (
            f"static constexpr std::array<std::array<float, {n_col}>, {n_row}> {array_name}"
            + "{{"
        )
        cpp_decl += ",".join(rows)
        cpp_decl += "}};\n"
        return [feature_comment, cpp_decl]