#! /usr/bin/env python3

def get_scale_note(scale, step, offset=0):
    octave, scale_index = divmod(step, len(scale))
    result = scale[scale_index]

    offset_step = -1 if offset < 0 else 1

    while offset != 0:
        while True:
            octave, result = divmod(result + offset_step + (octave * 12), 12)
            if result not in scale:
                break

        offset = offset - offset_step

    result += octave * 12
    return result

import unittest

class TestScaleNote(unittest.TestCase):
    def test_get_scale_note(self):
        scale = [0, 2, 4, 5, 7, 9, 11]

        self.assertEqual(get_scale_note(scale, 0), 0)
        self.assertEqual(get_scale_note(scale, 3), 5)
        self.assertEqual(get_scale_note(scale, 6), 11)
        self.assertEqual(get_scale_note(scale, 7), 12)
        self.assertEqual(get_scale_note(scale, 13), 23)
        self.assertEqual(get_scale_note(scale, 14), 24)

        self.assertEqual(get_scale_note(scale, -1), -1)
        self.assertEqual(get_scale_note(scale, -4), -7)
        self.assertEqual(get_scale_note(scale, -7), -12)
        self.assertEqual(get_scale_note(scale, -8), -13)

    def test_get_scale_note_offset(self):
        scale = [0, 2, 4, 5, 7, 9, 11]

        self.assertEqual(get_scale_note(scale, 3, -1), 3)
        self.assertEqual(get_scale_note(scale, 3, -2), 1)
        self.assertEqual(get_scale_note(scale, 3, -3), -2)

        self.assertEqual(get_scale_note(scale, 10, 1), 18)
        self.assertEqual(get_scale_note(scale, 10, 2), 20)
        self.assertEqual(get_scale_note(scale, 10, 3), 22)

if __name__ == '__main__':
    unittest.main()