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"""Test gmxapi._gmxapi file I/O routines."""
import os
import tempfile

import pytest
import gmxapi
import gmxapi.simulation.fileio
from gmxapi import _gmxapi


@pytest.mark.usefixtures('cleandir')
def test_core_read_tpr(spc_water_box):
    tpr_filehandle: _gmxapi.TprFile = _gmxapi.read_tprfile(os.fsencode(spc_water_box))
    parameters: _gmxapi.SimulationParameters = tpr_filehandle.params()
    assert 'nsteps' in parameters.extract()
    assert 'foo' not in parameters.extract()
    assert parameters.extract()['nsteps'] == 2


@pytest.mark.usefixtures('cleandir')
def test_core_rewrite_tprfile(spc_water_box):
    """Test _gmxapi.rewrite_tprfile for update of end_time.

    Set a new end time that is 5000 steps later than the original. Read dt
    from file to avoid floating point round-off errors.

    Transitively test gmx.fileio.read_tpr()
    """
    tpr_filename = spc_water_box
    additional_steps = 5000
    tpr_filehandle: _gmxapi.TprFile = _gmxapi.read_tprfile(os.fsencode(spc_water_box))
    params = tpr_filehandle.params().extract()
    dt = params['dt']
    nsteps = params['nsteps']
    init_step = params['init-step']
    initial_endtime = (init_step + nsteps) * dt
    new_endtime = initial_endtime + additional_steps * dt
    _, temp_filename = tempfile.mkstemp(suffix='.tpr')
    _gmxapi.rewrite_tprfile(source=tpr_filename, destination=temp_filename, end_time=new_endtime)
    tprfile = gmxapi.simulation.fileio.TprFile(temp_filename, 'r')
    with tprfile as fh:
        params = gmxapi.simulation.fileio.read_tpr(fh).parameters.extract()
        dt = params['dt']
        nsteps = params['nsteps']
        init_step = params['init-step']
        assert (init_step + nsteps) * dt == new_endtime

    os.unlink(temp_filename)


@pytest.mark.usefixtures('cleandir')
def test_core_read_and_write_tpr_file(spc_water_box):
    """Test gmx.fileio.write_tpr_file() using gmx.core API.
    """
    additional_steps = 5000

    tpr_filehandle: _gmxapi.TprFile = _gmxapi.read_tprfile(os.fsencode(spc_water_box))
    sim_input: _gmxapi.SimulationParameters = tpr_filehandle.params()
    params: dict = sim_input.extract()
    nsteps = params['nsteps']
    init_step = params['init-step']

    # Choose a new nsteps to check integer parameter setting.
    new_nsteps = init_step + additional_steps
    # Choose a new dt to check floating point parameter setting
    new_dt = params['dt'] * 2.

    sim_input.set('nsteps', new_nsteps)
    sim_input.set('dt', new_dt)

    _, temp_filename = tempfile.mkstemp(suffix='.tpr')
    _gmxapi.write_tprfile(temp_filename, sim_input)

    tprfile = gmxapi.simulation.fileio.TprFile(temp_filename, 'r')
    with tprfile as fh:
        params = gmxapi.simulation.fileio.read_tpr(fh).parameters.extract()
        # Note that we have chosen an exactly representable dt for spc_water_box.
        # Otherwise, we would have to use pytest.approx with a suitable tolerance.
        assert params['dt'] == new_dt
        assert params['nsteps'] != nsteps
        assert params['nsteps'] == new_nsteps

    os.unlink(temp_filename)
