import StringIO
import IMP
import IMP.test
import IMP.atom

class Tests(IMP.test.TestCase):
    """Test ForceSwitch"""

    def test_create(self):
        """Check ForceSwitch creation"""
        s = IMP.atom.ForceSwitch(5.0, 6.0)
        if IMP.base.get_check_level() != IMP.base.NONE:
            self.assertRaises(IMP.base.UsageException, IMP.atom.ForceSwitch,
                              6.0, 5.0)

    def test_value(self):
        """Check value of ForceSwitch"""
        s = IMP.atom.ForceSwitch(5.0, 6.0)

        # dist < min_distance should be unchanged
        for dist in (0, 1, 2, 3, 4, 5):
            self.assertEqual(s(100.0, dist), 100.0)
            self.assertEqual(s(100.0, 0.0, dist)[0], 100.0)
        # dist > min_distance should be zero
        for dist in (7, 8, 9, 10):
            self.assertEqual(s(100.0, dist), 0.0)
            self.assertEqual(s(100.0, 0.0, dist)[0], 0.0)

    def test_deriv(self):
        """Check derivatives of ForceSwitch"""
        s = IMP.atom.ForceSwitch(3.0, 6.0)
        def func(val):
            return s(100.0, val)

        for dist in range(10):
            score, deriv = s(100.0, 0.0, dist)
            num_deriv = IMP.test.numerical_derivative(func, dist, 0.01)
            self.assertAlmostEqual(deriv, num_deriv, delta=1e-4)

if __name__ == '__main__':
    IMP.test.main()