import importlib.util
import pathlib
import threading
import time
import unittest


ROOT = pathlib.Path(__file__).resolve().parents[1]
MODULE_PATH = ROOT / "app" / "services" / "task_serial_executor.py"
spec = importlib.util.spec_from_file_location("task_serial_executor", MODULE_PATH)
if spec is None or spec.loader is None:
    raise ImportError("task_serial_executor module spec not found")
task_serial_executor = importlib.util.module_from_spec(spec)
spec.loader.exec_module(task_serial_executor)
SerialTaskExecutor = task_serial_executor.SerialTaskExecutor


class TestTaskSerialExecutor(unittest.TestCase):
    def test_executor_runs_tasks_one_by_one(self):
        executor = SerialTaskExecutor()
        state_lock = threading.Lock()
        state = {"active": 0, "peak_active": 0}

        def critical_work():
            with state_lock:
                state["active"] += 1
                state["peak_active"] = max(state["peak_active"], state["active"])
            time.sleep(0.05)
            with state_lock:
                state["active"] -= 1

        threads = [threading.Thread(target=lambda: executor.run(critical_work)) for _ in range(2)]
        for t in threads:
            t.start()
        for t in threads:
            t.join()

        self.assertEqual(state["peak_active"], 1)


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