# tests/test_tank.py
import numpy as np
import pytest
from tank_pipe.tank import Tank


GAMMA = 1.4
R_GAS = 287.0


def test_tank_initial_state_matches_ideal_gas():
    """
    Given P, T, V construct a Tank; mass and U should match ideal gas:
      rho  = P / (R * T)
      mass = rho * V
      U    = P * V / (gamma - 1)     (since u=0 inside tank)
      T    = (U / mass) * (gamma - 1) / R   (round-trip)
    """
    tank = Tank(V=5.0, P_init=10e6, T_init=300.0, gamma=GAMMA, R_gas=R_GAS)
    rho_expected = 10e6 / (R_GAS * 300.0)
    assert abs(tank.rho - rho_expected) < 1e-9
    assert abs(tank.mass - rho_expected * 5.0) < 1e-6
    assert abs(tank.U - 10e6 * 5.0 / (GAMMA - 1)) < 1e-3
    assert abs(tank.P - 10e6) < 1e-3
    assert abs(tank.T - 300.0) < 1e-9


def test_tank_ghost_state_is_stagnation_conservative_vector():
    """
    ghost_state() should return [rho, 0, P/(gamma-1)]
    (u_ghost = 0 per spec §2.3, so total energy density equals
    internal energy density = P/(gamma-1)).
    """
    tank = Tank(V=5.0, P_init=10e6, T_init=300.0, gamma=GAMMA, R_gas=R_GAS)
    g = tank.ghost_state()
    assert g.shape == (3,)
    assert abs(g[0] - tank.rho) < 1e-12
    assert g[1] == 0.0
    assert abs(g[2] - 10e6 / (GAMMA - 1)) < 1e-3


def test_tank_apply_flux_outflow_reduces_mass_energy_and_pressure():
    """
    apply_flux(mdot, edot, dt, sign=-1) should subtract mdot*dt from mass
    and edot*dt from U. Derived P should decrease correspondingly.
    """
    tank = Tank(V=5.0, P_init=10e6, T_init=300.0, gamma=GAMMA, R_gas=R_GAS)
    mass_before = tank.mass
    U_before = tank.U
    P_before = tank.P
    mdot = 1.0      # kg/s
    edot = 5e5      # J/s (enthalpy rate)
    dt = 1e-3
    tank.apply_flux(mdot=mdot, edot=edot, dt=dt, sign=-1)
    assert abs(tank.mass - (mass_before - mdot * dt)) < 1e-12
    assert abs(tank.U    - (U_before    - edot * dt)) < 1e-9
    assert tank.P < P_before