import sys, os
from threading import Thread
from queue    import Queue, Empty

_root = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
_gui  = os.path.dirname(os.path.abspath(__file__))
for _p in [_root, _gui]:
    if _p not in sys.path:
        sys.path.insert(0, _p)

from a_backend     import ABackend
from a_transceiver import ATransceiver
from msg.container import MsgContainer


class SerialBackend(ABackend):
    """Backend that reads from a serial (COM / tty) port."""

    def __init__(self, port: str, baud_rate: int = 115200):
        self._port    = port
        self._baud    = baud_rate
        self._serial  = None
        self._xcvr    = None
        self._running = False
        self._queue: Queue = Queue()
        self._thread  = Thread(target=self._run, daemon=True)

    def register_xcvr(self, xcvr):
        self._xcvr = xcvr
        xcvr.on_register(self)

    def send(self, xcvr: ATransceiver, data: bytes):
        self._queue.put(data)

    def connect(self):
        import serial
        self._serial  = serial.Serial(self._port, self._baud, timeout=0.1)
        self._running = True

    def start(self):
        self._thread.start()

    def stop(self):
        self._running = False
        if self._thread.is_alive():
            self._thread.join(timeout=2.0)

    def disconnect(self):
        if self._serial and self._serial.is_open:
            self._serial.close()

    def _run(self):
        while self._running:
            try:
                data = self._serial.read(64)
                if data and self._xcvr:
                    self._xcvr.on_recv(MsgContainer(data, self._xcvr))
                # Drain outgoing queue
                while True:
                    try:
                        self._serial.write(self._queue.get_nowait())
                    except Empty:
                        break
            except Exception:
                self._running = False
                break