from .fleet_cost_per_mile_types import CostPerMile, WholeLifeCosts
from .math_round_div import round_div
from .money_amount import Money
from .money_sum import sum_money


def _tenths(amount: Money, miles: int) -> int:
    return round_div(amount.minor * 10, miles, "half-up")


def _display(value: int) -> str:
    sign = "-" if value < 0 else ""
    magnitude = abs(value)
    return "%s%d.%d" % (sign, magnitude // 10, magnitude % 10)


def cost_per_mile(costs: WholeLifeCosts, miles: int) -> CostPerMile:
    """Whole-life cost per mile, in tenths of a penny, the unit fleet reports use.

    Each part is rounded on its own for the breakdown, and the total is rounded
    from the total cost: adding up the rounded parts drifts by a tenth or two,
    which is why the total is not their sum.
    """
    if isinstance(miles, bool) or not isinstance(miles, int) or miles <= 0:
        raise ValueError("miles must be a whole number above zero, received %r" % (miles,))
    total_cost = sum_money(
        [costs.depreciation, costs.fuel, costs.maintenance, costs.insurance, costs.tax],
        costs.depreciation.currency,
    )
    total_tenths = _tenths(total_cost, miles)
    return CostPerMile(
        total_cost=total_cost,
        depreciation_tenths=_tenths(costs.depreciation, miles),
        fuel_tenths=_tenths(costs.fuel, miles),
        maintenance_tenths=_tenths(costs.maintenance, miles),
        insurance_tenths=_tenths(costs.insurance, miles),
        tax_tenths=_tenths(costs.tax, miles),
        total_tenths=total_tenths,
        per_mile=_display(total_tenths),
    )