import ast
import pathlib
import unittest


ROOT = pathlib.Path(__file__).resolve().parents[1]


def load_bridge_helper(name):
    source = (ROOT / "bridge.py").read_text()
    module = ast.parse(source)
    for node in module.body:
        if isinstance(node, ast.FunctionDef) and node.name == name:
            namespace = {}
            exec(compile(ast.Module([node], []), "bridge.py", "exec"), namespace)
            return namespace[name]
    raise AssertionError(f"bridge.py helper not found: {name}")


class BridgeBackportTests(unittest.TestCase):
    def test_dmrd_seq_delta_is_modulo_256(self):
        dmrd_seq_delta = load_bridge_helper("dmrd_seq_delta")

        self.assertIsNone(dmrd_seq_delta(1, False))
        self.assertEqual(dmrd_seq_delta(2, 1), 1)
        self.assertEqual(dmrd_seq_delta(0, 255), 1)
        self.assertEqual(dmrd_seq_delta(2, 255), 3)
        self.assertEqual(dmrd_seq_delta(250, 2), 248)


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