import unittest
from typing import Optional
import dataclasses


@dataclasses.dataclass
class Citation:
    volume: int
    chapter: int
    line: int


def parse(src: str) -> Optional[Citation]:
    try:
        volume, chapter, line = src.split(".")
        volume = int(volume)
        chapter = int(chapter)
        line = int(line)
        if volume <= 0 or chapter <= 0 or line <= 0:
            raise ValueError(f"Invalid citation point {volume}.{chapter}.{line}")
        return Citation(volume, chapter, line)
    except ValueError:
        return None


class TestCitation(unittest.TestCase):
    def test_parse(self):
        self.assertEqual(parse("1.2.3"), Citation(1, 2, 3))
        self.assertEqual(parse("1.2.0"), None)
        self.assertEqual(parse("(I.2.3)"), None)
        self.assertEqual(parse("I.5.1"), None)
        self.assertEqual(parse(""), None)


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