# This tests calculates the force on the atoms of a small molecule.
#
# If the test fails, set the fd boolean below to enable a (costly) finite
# difference check.

import numpy as np
import pytest
from ase.build import molecule

from gpaw import GPAW
from gpaw.atom.basis import BasisMaker


@pytest.mark.old_gpaw_only  # basis set cutoff?
def test_lcao_force():
    obasis = BasisMaker.from_symbol('O').generate(2, 1, energysplit=0.3,
                                                  tailnorm=0.03**.5)
    hbasis = BasisMaker.from_symbol('H').generate(2, 1, energysplit=0.3,
                                                  tailnorm=0.03**.5)
    basis = {'O': obasis, 'H': hbasis}

    system = molecule('H2O')
    system.center(vacuum=1.5)
    system.rattle(stdev=.2, seed=42)
    system.set_pbc(1)

    calc = GPAW(h=0.2,
                mode='lcao',
                basis=basis,
                kpts=[(0., 0., 0.), (.3, .1, .4)],
                convergence={'density': 1e-5, 'energy': 1e-6})

    system.calc = calc

    # Previous FD result, generated by disabled code below
    F_ac_ref = np.array([[1.05022478, 1.63103681, -5.00612007],
                         [-0.69739179, -0.89624274, 3.03203147],
                         [-0.34438181, -0.7042696, 1.77209023]])

    for use_rho in [0, 1]:
        if use_rho:
            for kpt in calc.wfs.kpt_u:
                kpt.rho_MM = calc.wfs.calculate_density_matrix(kpt.f_n,
                                                               kpt.C_nM)

        F_ac = system.get_forces()
        system.calc.results.pop('forces')

        err_ac = np.abs(F_ac - F_ac_ref)
        err = err_ac.max()

        print('Force')
        print(F_ac)
        print()
        print('Reference result')
        print(F_ac_ref)
        print()
        print('Error')
        print(err_ac)
        print()
        print('Max error')
        print(err)

        # ASE uses dx = [+|-] 0.001 by default,
        # error should be around 2e-3.
        # In fact 4e-3 would probably be acceptable
        assert err < 3e-3

    # Set boolean to run new FD check
    fd = False

    if fd:
        from gpaw.test import calculate_numerical_forces
        F_ac_fd = calculate_numerical_forces(system, 0.001)
        print('Self-consistent forces')
        print(F_ac)
        print('FD')
        print(F_ac_fd)
        print(repr(F_ac_fd))
        print(F_ac - F_ac_fd, np.abs(F_ac - F_ac_fd).max())

        assert np.abs(F_ac - F_ac_fd).max() < 4e-3
