from __future__ import annotations

import pytest

from domain.fuel_rates.fuel import Fuel, UnpricedFuel
from domain.fuel_rates.fuel_rates import FuelRate, FuelRates


def _rates() -> FuelRates:
    return FuelRates(
        period="test",
        seg_export_p_per_kwh=15.0,
        rates={Fuel.MAINS_GAS: FuelRate(unit_rate_p_per_kwh=5.74, standing_charge_p_per_day=29.09)},
    )


def test_unit_rate_and_standing_charge_read_back_for_a_priced_fuel() -> None:
    # Arrange
    rates = _rates()

    # Act / Assert
    assert rates.unit_rate_p_per_kwh(Fuel.MAINS_GAS) == 5.74
    assert rates.standing_charge_p_per_day(Fuel.MAINS_GAS) == 29.09


def test_a_fuel_absent_from_the_snapshot_raises_unpriced_fuel() -> None:
    # Arrange — LPG is not in this snapshot.
    rates = _rates()

    # Act / Assert — the raise carries the offending fuel for the operator.
    with pytest.raises(UnpricedFuel) as excinfo:
        rates.unit_rate_p_per_kwh(Fuel.LPG)
    assert excinfo.value.fuel is Fuel.LPG