import asyncio
import json


# Default: broadcast (6 bytes). Pi always sends 6-byte address + payload to ESP32.
BROADCAST_MAC = bytes.fromhex("ffffffffffff")


def _encode_payload(data):
    if isinstance(data, str):
        return data.encode()
    if isinstance(data, dict):
        return json.dumps(data).encode()
    return data


def _parse_mac(addr):
    """Convert 12-char hex string or 6-byte bytes to 6-byte MAC."""
    if addr is None or addr == b"":
        return BROADCAST_MAC
    if isinstance(addr, bytes) and len(addr) == 6:
        return addr
    if isinstance(addr, str) and len(addr) == 12:
        return bytes.fromhex(addr)
    return BROADCAST_MAC


async def _to_thread(func, *args):
    to_thread = getattr(asyncio, "to_thread", None)
    if to_thread:
        return await to_thread(func, *args)
    loop = asyncio.get_event_loop()
    return await loop.run_in_executor(None, func, *args)


class NullSender:
    """Used when no ESP-NOW UART bridge is configured or the port cannot be opened."""

    async def send(self, data, addr=None):
        return True


class SerialSender:
    def __init__(self, port, baudrate, default_addr=None):
        import serial

        self._serial = serial.Serial(port, baudrate=baudrate, timeout=1)
        self._default_addr = _parse_mac(default_addr)
        self._write_lock = asyncio.Lock()

    async def send(self, data, addr=None):
        mac = _parse_mac(addr) if addr is not None else self._default_addr
        payload = _encode_payload(data)
        async with self._write_lock:
            await _to_thread(self._serial.write, mac + payload)
        return True


_current_sender = None


def set_sender(sender):
    global _current_sender
    _current_sender = sender


def get_current_sender():
    return _current_sender


def get_sender(settings):
    # Serial ESP-NOW bridge is opt-in (serial_enabled true); default off for dev / Wi-Fi-only.
    if not settings.get("serial_enabled"):
        print("[startup] serial bridge disabled (set serial_enabled true in settings.json to enable)")
        return NullSender()
    port = settings.get("serial_port", "/dev/ttyS0")
    raw_port = str(port).strip() if port is not None else ""
    if not raw_port or raw_port.lower() in ("none", "off"):
        print("[startup] serial bridge disabled (empty serial_port)")
        return NullSender()
    baudrate = settings.get("serial_baudrate", 912000)
    default_addr = settings.get("serial_destination_mac", "ffffffffffff")
    try:
        return SerialSender(raw_port, baudrate, default_addr=default_addr)
    except Exception as e:
        print(
            f"[startup] serial open failed ({raw_port!r}): {e}; "
            "continuing without ESP-NOW bridge (Wi-Fi drivers unchanged)"
        )
        return NullSender()