from decimal import Decimal, ROUND_HALF_UP


def money(value):
    return Decimal(str(value)).quantize(Decimal("0.01"), rounding=ROUND_HALF_UP)


def calculate_costs(gross, vat_rate=23, vat_deduction_percent=50):
    gross = Decimal(str(gross)); rate = Decimal(str(vat_rate))
    deduction = Decimal(str(vat_deduction_percent)) / Decimal("100")
    net = gross / (Decimal("1") + rate / Decimal("100")); vat = gross - net
    deductible_vat = vat * deduction
    return {"gross": money(gross), "net": money(net), "vat": money(vat),
            "deductible_vat": money(deductible_vat), "final_cost": money(gross - deductible_vat)}


def calculate_net_price_costs(net_price, vat_rate=23, vat_deduction_percent=50):
    """Return per-unit invoice and effective costs for a net fuel price.

    A 50% VAT deduction means the company bears half of the VAT, not a 50% VAT rate.
    """
    net = Decimal(str(net_price))
    rate = Decimal(str(vat_rate)) / Decimal("100")
    deduction = Decimal(str(vat_deduction_percent)) / Decimal("100")
    deduction = min(max(deduction, Decimal("0")), Decimal("1"))
    vat = net * rate
    invoice_gross = net + vat
    deductible_vat = vat * deduction
    effective_cost = invoice_gross - deductible_vat
    return {
        "net": net,
        "vat": vat,
        "invoice_gross": invoice_gross,
        "deductible_vat": deductible_vat,
        "effective_cost": effective_cost,
    }