# tests/cryo_tank/test_tank_model.py
"""Tests for CryoTank model."""
import pytest
import numpy as np
from cryo_tank.tank_model import CryoTank
from cryo_tank.heat_leak import MLIHeatLeak
from cryo_tank.config import (
    V_TOTAL, H_TANK, A_CROSS, A_TOTAL, P_WORKING,
    T_INIT, ULLAGE_FRACTION,
    MDOT_IN_LN2, T_IN_LN2, MDOT_OUT_LN2, T_IN_HE,
    H_CONV_SURFACE, T_ENV,
)


def _make_tank(**overrides):
    """Create a CryoTank with default config and MLI heat leak."""
    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 TestGeometry:

    def test_cross_section_area(self):
        tank = _make_tank()
        assert abs(tank.A_cross - 0.8402) < 0.001

    def test_total_surface_area(self):
        tank = _make_tank()
        assert abs(tank.A_total - 3.305) < 0.01

    def test_wetted_area_at_70_percent_fill(self):
        tank = _make_tank()
        level = 0.7 * H_TANK  # 0.35 m
        A_wet, A_dry = tank.wetted_areas(level)
        # A_wet = bottom cap + side * level
        expected_wet = A_CROSS + np.pi * tank.D * level
        assert abs(A_wet - expected_wet) < 0.01
        assert abs(A_wet + A_dry - A_TOTAL) < 0.01


class TestInitialState:

    def test_initial_liquid_mass(self):
        tank = _make_tank()
        y0 = tank.initial_state()
        m_liq = y0[0]
        # rho_LN2(78K, 0.17MPa) ~ 803.3 kg/m3, V_liq = 0.2941 m3
        assert 235 < m_liq < 237  # ~236.25 kg

    def test_initial_fill_fraction(self):
        tank = _make_tank()
        y0 = tank.initial_state()
        info = tank.derive(y0)
        assert abs(info['fill_fraction'] - 0.70) < 0.01

    def test_initial_temperatures(self):
        tank = _make_tank()
        y0 = tank.initial_state()
        info = tank.derive(y0)
        assert abs(info['T_liq'] - T_INIT) < 0.1
        assert abs(info['T_ull'] - T_INIT) < 1.0

    def test_initial_pressure_is_provided_entirely_by_helium(self):
        tank = _make_tank()
        y0 = tank.initial_state()
        info = tank.derive(y0)
        P_He = info['P_He']
        assert abs(P_He - P_WORKING) / P_WORKING < 1e-12


class TestVolumeRate:

    def test_ullage_volume_rate_includes_liquid_thermal_expansion(self):
        tank = _make_tank(
            mdot_in_ln2=0.0,
            mdot_out_ln2=0.0,
            h_conv=0.0,
        )
        y0 = tank.initial_state()
        info = tank.derive(y0)

        Q_liq_to_ull = 0.0
        Q_leak = tank.heat_leak_model.compute(info['T_liq'], tank.T_env)
        A_wet, A_dry = tank.wetted_areas(info['liquid_level'])
        Q_leak_liq = Q_leak * A_wet / (A_wet + A_dry)
        dU_liq_dt = tank._liquid_energy_rate(
            info, Q_liq_to_ull, Q_leak_liq
        )

        dV_ull_dt = tank._ullage_volume_rate(
            info, tank.dm_liq_dt, dU_liq_dt
        )

        y_next = y0.copy()
        dt = 1.0
        y_next[1] += dU_liq_dt * dt
        finite_difference = (
            tank.derive(y_next)['V_ull'] - info['V_ull']
        ) / dt

        assert dV_ull_dt < 0.0
        assert abs(dV_ull_dt - finite_difference) / abs(finite_difference) < 1e-5