import pytest

from reactor_sim.state import CoolantLoopState, TurbineState
from reactor_sim.turbine import Turbine


def test_turbine_spools_toward_target_output():
    turbine = Turbine()
    loop = CoolantLoopState(
        temperature_in=600.0,
        temperature_out=650.0,
        pressure=6.0,
        mass_flow_rate=20_000.0,
        steam_quality=0.9,
    )
    state = TurbineState(
        steam_enthalpy=0.0,
        shaft_power_mw=0.0,
        electrical_output_mw=0.0,
        condenser_temperature=300.0,
    )
    target_electric = min(
        turbine.rated_output_mw, 300.0 * turbine.mechanical_efficiency * turbine.generator_efficiency
    )

    dt = 5.0
    turbine.step(loop, state, steam_power_mw=300.0, dt=dt)
    assert 0.0 < state.electrical_output_mw < target_electric

    for _ in range(5):
        turbine.step(loop, state, steam_power_mw=300.0, dt=dt)

    assert state.electrical_output_mw == pytest.approx(target_electric, rel=0.05)


def test_turbine_produces_no_power_without_steam():
    turbine = Turbine()
    loop = CoolantLoopState(
        temperature_in=295.0,
        temperature_out=295.0,
        pressure=6.0,
        mass_flow_rate=20_000.0,
        steam_quality=0.0,
    )
    state = TurbineState(
        steam_enthalpy=0.0,
        shaft_power_mw=0.0,
        electrical_output_mw=0.0,
        condenser_temperature=300.0,
    )

    turbine.step(loop, state, steam_power_mw=0.0, dt=1.0)

    assert state.electrical_output_mw == 0.0
    assert state.shaft_power_mw == 0.0