import pytest
import ase.units as units
from ase.calculators.tip3p import TIP3P, epsilon0, sigma0, rOH, angleHOH
from ase.calculators.qmmm import SimpleQMMM, EIQMMM, LJInteractions
from ase.data.s22 import create_s22_system as s22
from ase.md.verlet import VelocityVerlet
from ase.constraints import FixBondLengths


@pytest.mark.slow
def test_rattle(testdir):

    i = LJInteractions({('O', 'O'): (epsilon0, sigma0)})

    for calc in [TIP3P(),
                 SimpleQMMM([0, 1, 2], TIP3P(), TIP3P(), TIP3P()),
                 EIQMMM([0, 1, 2], TIP3P(), TIP3P(), i)]:
        dimer = s22('Water_dimer')

        for m in [0, 3]:
            dimer.set_angle(m + 1, m, m + 2, angleHOH)
            dimer.set_distance(m, m + 1, rOH, fix=0)
            dimer.set_distance(m, m + 2, rOH, fix=0)

        fixOH1 = [(3 * i, 3 * i + 1) for i in range(2)]
        fixOH2 = [(3 * i, 3 * i + 2) for i in range(2)]
        fixHH = [(3 * i + 1, 3 * i + 2) for i in range(2)]
        dimer.set_constraint(FixBondLengths(fixOH1 + fixOH2 + fixHH))

        dimer.calc = calc

        e = dimer.get_potential_energy()
        with VelocityVerlet(dimer, 8.0 * units.fs,
                            trajectory=calc.name + '.traj',
                            logfile=calc.name + '.log',
                            loginterval=5) as md:
            md.run(25)
        de = dimer.get_potential_energy() - e
        assert abs(de - -0.028) < 0.001
