import argparse
import sys
import threading
import time


def _load_serial():
    try:
        import serial  # type: ignore
    except ImportError:
        sys.stderr.write("pyserial is not installed. Run: pip install pyserial\n")
        sys.stderr.flush()
        sys.exit(2)
    return serial


def _reader_loop(ser, stop_event):
    buffer = bytearray()
    while not stop_event.is_set():
        try:
            data = ser.read(ser.in_waiting or 1)
        except Exception as exc:
            sys.stderr.write(f"serial read error: {exc}\n")
            sys.stderr.flush()
            break

        if data:
            buffer.extend(data)
            while b"\n" in buffer:
                line, _, rest = buffer.partition(b"\n")
                buffer = bytearray(rest)
                text = line.decode("utf-8", errors="replace").rstrip("\r")
                sys.stdout.write(text + "\n")
                sys.stdout.flush()
        else:
            time.sleep(0.01)

    if buffer:
        text = buffer.decode("utf-8", errors="replace").rstrip("\r")
        sys.stdout.write(text + "\n")
        sys.stdout.flush()


def main():
    parser = argparse.ArgumentParser(description="UART bridge using pyserial.")
    parser.add_argument("--port", required=True, help="COM port name, e.g. COM3")
    parser.add_argument("--baud", type=int, required=True, help="Baud rate")
    args = parser.parse_args()

    serial = _load_serial()

    try:
        ser = serial.Serial(args.port, args.baud, timeout=0.1, write_timeout=1)
    except Exception as exc:
        sys.stderr.write(f"failed to open {args.port} @ {args.baud}: {exc}\n")
        sys.stderr.flush()
        return 1

    sys.stdout.write(f"[UART] OPEN {args.port} @ {args.baud}\n")
    sys.stdout.flush()

    stop_event = threading.Event()
    reader = threading.Thread(target=_reader_loop, args=(ser, stop_event), daemon=True)
    reader.start()

    try:
        for line in sys.stdin:
            command = line.rstrip("\n")
            if command == "__exit__":
                break
            if not command:
                continue
            try:
                ser.write(command.encode("utf-8") + b"\r\n")
                ser.flush()
            except Exception as exc:
                sys.stderr.write(f"serial write error: {exc}\n")
                sys.stderr.flush()
                break
    finally:
        stop_event.set()
        try:
            ser.close()
        except Exception:
            pass

    return 0


if __name__ == "__main__":
    raise SystemExit(main())