import numpy as np
import pytest

from gas_cylinder import (
    DEFAULT_FLUID,
    DEFAULT_P_INIT,
    DEFAULT_T_INIT,
    DEFAULT_VOLUME,
    HighPressureGasCylinder,
)


def test_default_high_pressure_cylinder_state_matches_inputs():
    cylinder = HighPressureGasCylinder()

    assert cylinder.fluid == DEFAULT_FLUID
    assert cylinder.V == DEFAULT_VOLUME
    assert abs(cylinder.P - DEFAULT_P_INIT) / DEFAULT_P_INIT < 1e-8
    assert abs(cylinder.T - DEFAULT_T_INIT) < 1e-8
    assert cylinder.mass > 0
    assert cylinder.U > 0
    assert cylinder.gamma > 1.0
    assert cylinder.compressibility_factor > 0.0


def test_cylinder_accepts_configurable_fluid_pressure_volume_temperature():
    cylinder = HighPressureGasCylinder(
        fluid="Nitrogen",
        P_init=2.0e6,
        V=50e-3,
        T_init=300.0,
    )

    assert cylinder.fluid == "Nitrogen"
    assert abs(cylinder.P - 2.0e6) / 2.0e6 < 1e-8
    assert abs(cylinder.T - 300.0) < 1e-8
    assert abs(cylinder.V - 50e-3) < 1e-15
    assert cylinder.mass > 0


def test_cylinder_ghost_state_is_stagnant_conservative_vector():
    cylinder = HighPressureGasCylinder()
    ghost = cylinder.ghost_state()

    assert ghost.shape == (3,)
    assert abs(ghost[0] - cylinder.rho) < 1e-12
    assert ghost[1] == 0.0
    assert abs(ghost[2] - cylinder.rho * cylinder.specific_internal_energy) < 1e-6


def test_cylinder_apply_flux_outflow_reduces_mass_energy_and_pressure():
    cylinder = HighPressureGasCylinder()
    mass_before = cylinder.mass
    U_before = cylinder.U
    P_before = cylinder.P

    mdot = 1e-3
    edot = mdot * cylinder.h
    dt = 1.0
    cylinder.apply_flux(mdot=mdot, edot=edot, dt=dt, sign=-1)

    assert abs(cylinder.mass - (mass_before - mdot * dt)) < 1e-12
    assert abs(cylinder.U - (U_before - edot * dt)) < 1e-6
    assert cylinder.P < P_before


def test_cylinder_rejects_invalid_inputs():
    with pytest.raises(ValueError):
        HighPressureGasCylinder(fluid="")
    with pytest.raises(ValueError):
        HighPressureGasCylinder(P_init=0.0)
    with pytest.raises(ValueError):
        HighPressureGasCylinder(V=0.0)
    with pytest.raises(ValueError):
        HighPressureGasCylinder(T_init=0.0)