from .math_round_div import RoundingMode, round_div
from .money_amount import Money, money


def apply_rate(amount: Money, basis_points: int, mode: RoundingMode = "half-up") -> Money:
    """Apply a rate given in basis points (10000 = 100%).

    Rates are integers, never floats, so VAT, discounts, interest and
    commission all stay in exact arithmetic right up to the single rounding
    step the caller asked for.
    """
    if isinstance(basis_points, bool) or not isinstance(basis_points, int):
        raise TypeError("basis_points must be an integer, received %r" % (basis_points,))
    return money(round_div(amount.minor * basis_points, 10000, mode), amount.currency)


def apply_rate_complement(amount: Money, basis_points: int, mode: RoundingMode = "half-up") -> Money:
    """The complement: what is left after the rate is taken off."""
    return money(amount.minor - apply_rate(amount, basis_points, mode).minor, amount.currency)