import sys,os,unittest
from ctypes import *
from lammps import lammps

# add timestep dependent force
def callback_one(lmp, ntimestep, nlocal, tag, x, f):
    for i in range(nlocal):
        f[i][0] = float(ntimestep)
        f[i][1] = float(ntimestep)
        f[i][2] = float(ntimestep)

class PythonExternal(unittest.TestCase):
    def testExternalCallback(self):
        """Test fix external from Python with pf/callback"""

        machine=None
        if 'LAMMPS_MACHINE_NAME' in os.environ:
            machine=os.environ['LAMMPS_MACHINE_NAME']
        lmp=lammps(name=machine, cmdargs=['-nocite', '-log','none', '-echo', 'screen'])

        # a few commands to set up simple system
        basic_system="""lattice sc 1.0
                        region box block -1 1 -1 1 -1 1
                        create_box 1 box
                        create_atoms 1 box
                        mass 1 1.0
                        pair_style zero 0.1
                        pair_coeff 1 1
                        velocity all set 0.1 0.0 -0.1
                        thermo 5
                        fix 1 all nve
                        fix ext all external pf/callback 5 1
"""
        lmp.commands_string(basic_system)
        lmp.set_fix_external_callback("ext",callback_one,lmp)
        lmp.command("run 10 post no")
        self.assertAlmostEqual(lmp.get_thermo("temp"),1.0/30.0,14)

##############################
if __name__ == "__main__":
    unittest.main()