import pytest
import numpy as np

from ase import Atoms


@pytest.fixture
def dimer_params():
    dimer_params = {}
    a = 2.0
    dimer_params["symbols"] = "Ni" * 2
    dimer_params["positions"] = [(0, 0, 0), (a, 0, 0)]
    dimer_params["cell"] = (1000 * a, 1000 * a, 1000 * a)
    dimer_params["pbc"] = (False, False, False)
    return dimer_params


@pytest.mark.calculator_lite
@pytest.mark.calculator("lammpslib")
def test_lammpslib_small_nonperiodic(factory, dimer_params, calc_params_NiH):
    """Test that lammpslib handle nonperiodic cases where the cell size
    in some directions is small (for example for a dimer)"""
    # Make a dimer in a nonperiodic box
    dimer = Atoms(**dimer_params)

    # Set of calculator
    calc = factory.calc(**calc_params_NiH)
    dimer.calc = calc

    # Check energy
    energy_ref = -1.10756669119
    energy = dimer.get_potential_energy()
    print("Computed energy: {}".format(energy))
    assert energy == pytest.approx(energy_ref, rel=1e-4)

    # Check forces
    forces_ref = np.array(
        [[-0.9420162329811532, 0.0, 0.0], [+0.9420162329811532, 0.0, 0.0]]
    )
    forces = dimer.get_forces()
    print("Computed forces:")
    print(np.array2string(forces))
    assert forces == pytest.approx(forces_ref, rel=1e-4)