import threading
from dataclasses import dataclass

def hex2b(s: str) -> bytes:
    return bytes(int(x, 16) for x in s.split())

@dataclass
class SerialConfig:
    port: str
    baudrate: int = 9600

class SerialBridge:
    def __init__(self, cfg: SerialConfig):
        self.cfg = cfg
        self._lock = threading.Lock()

    def busy(self):
        return self._lock.locked()

    def send_and_read_once(self, payload: bytes):
        if not self._lock.acquire(blocking=False):
            return {"busy": True, "error": "BUSY"}
        try:
            return {"ok": True, "request": payload.hex()}
        finally:
            self._lock.release()