"""Tests for Part XIV: differential model and stability checks."""

import numpy as np
from fqbm.state import FQBMState
from fqbm.system.differential_model import (
    solve_trajectory,
    check_stability,
    DifferentialParams,
)


def test_solve_trajectory():
    x0 = FQBMState(B=100, R=50, Loans=500, Deposits=600, E_b=50, S=1.0)
    params = DifferentialParams(monetary_shock=1.0, credit_cycle=0.01)
    t, X = solve_trajectory(x0, (0, 1), params, t_eval=np.linspace(0, 1, 11))
    assert t.shape[0] == 11
    assert X.shape == (11, 12)
    assert X[-1, 0] > X[0, 0]  # B increased
    assert X[-1, 1] > X[0, 1]  # R increased
    assert X[-1, 3] >= X[0, 3]  # Loans


def test_check_stability():
    x = FQBMState(R=100, Loans=1000, E_b=100)
    checks = check_stability(x, k=0.08, reserve_threshold=50, debt_gdp=0.5, r=0.05, g=0.02, primary_balance_gdp=0.02)
    assert "CR_ok" in checks
    assert "reserves_ok" in checks
    assert "debt_sustainable" in checks
    assert checks["CR_ok"] is True
    assert checks["reserves_ok"] is True