# tests/cryo_tank/test_integration.py
"""Integration tests for the cryogenic tank simulation."""
import numpy as np
from cryo_tank.tank_model import CryoTank
from cryo_tank.heat_leak import MLIHeatLeak
from cryo_tank.solver import run
from cryo_tank.config import (
    V_TOTAL, H_TANK, P_WORKING, T_INIT, ULLAGE_FRACTION,
    MDOT_IN_LN2, T_IN_LN2, MDOT_OUT_LN2, T_IN_HE,
    H_CONV_SURFACE, T_ENV, A_TOTAL,
)


def _make_tank(**overrides):
    """Create a tank with default config, allowing overrides."""
    kw = dict(
        V_total=V_TOTAL, H_tank=H_TANK,
        P_work=P_WORKING,
        T_init=T_INIT, ullage_fraction=ULLAGE_FRACTION,
        mdot_in_ln2=MDOT_IN_LN2, T_in_ln2=T_IN_LN2,
        mdot_out_ln2=MDOT_OUT_LN2,
        T_in_he=T_IN_HE,
        h_conv=H_CONV_SURFACE, T_env=T_ENV,
        heat_leak_model=MLIHeatLeak(A_total=A_TOTAL, q_mli=1.0),
    )
    kw.update(overrides)
    return CryoTank(**kw)


class TestMassConservation:

    def test_liquid_mass_change_matches_net_flow(self):
        """Over a short run, dm_liq should equal (mdot_in - mdot_out) * dt."""
        tank = _make_tank()
        history = run(tank, t_end=10.0, max_step=1.0)

        m_liq_0 = history['m_liq'][0]
        m_liq_f = history['m_liq'][-1]
        t_f = history['t'][-1]

        expected_dm = (MDOT_IN_LN2 - MDOT_OUT_LN2) * t_f
        actual_dm = m_liq_f - m_liq_0

        rel_err = abs(actual_dm - expected_dm) / abs(expected_dm)
        assert rel_err < 1e-6, f"Mass conservation error: rel_err={rel_err:.2e}"


class TestSteadyState:

    def test_zero_flow_zero_leak_is_static(self):
        """With no flow and no heat leak, state should not change."""
        tank = _make_tank(
            mdot_in_ln2=0.0,
            mdot_out_ln2=0.0,
            h_conv=0.0,
            heat_leak_model=MLIHeatLeak(A_total=A_TOTAL, q_mli=0.0),
        )
        history = run(tank, t_end=100.0, max_step=10.0)

        T_liq = history['T_liq']
        T_ull = history['T_ull']

        assert abs(T_liq[-1] - T_liq[0]) < 0.01, f"T_liq drifted: {T_liq[0]:.3f} -> {T_liq[-1]:.3f}"
        assert abs(T_ull[-1] - T_ull[0]) < 0.1, f"T_ull drifted: {T_ull[0]:.3f} -> {T_ull[-1]:.3f}"


class TestPhysicalBehavior:

    def test_liquid_level_decreases(self):
        """With net outflow, liquid level should decrease."""
        tank = _make_tank()
        history = run(tank, t_end=60.0, max_step=5.0)
        assert history['fill_fraction'][-1] < history['fill_fraction'][0]

    def test_he_flow_rate_positive(self):
        """He should always flow in (pressurization), not out."""
        tank = _make_tank()
        history = run(tank, t_end=60.0, max_step=5.0)
        assert np.all(history['mdot_He'] >= -1e-10)  # allow tiny numerical noise