"""MQTT client service for real-time entity updates.

Connects to an MQTT broker, subscribes to configured topics, and stores
the latest messages per topic.  The dashboard WebSocket pushes MQTT
state changes to connected clients.
"""

from __future__ import annotations

import asyncio
import json
import logging
import time
from dataclasses import dataclass, field
from typing import Any, Callable, Dict, List, Optional

import aiomqtt

logger = logging.getLogger(__name__)


@dataclass
class MqttMessage:
    """Single retained MQTT message."""

    topic: str
    payload: Any
    timestamp: float = field(default_factory=time.time)


class MqttService:
    """Async MQTT client that maintains a live topic→value store."""

    def __init__(self) -> None:
        self._store: Dict[str, MqttMessage] = {}
        self._client: Optional[aiomqtt.Client] = None
        self._task: Optional[asyncio.Task] = None
        self._listeners: List[Callable[[MqttMessage], Any]] = []
        self._connected = False
        self._config: Dict[str, Any] = {}

    @property
    def connected(self) -> bool:
        return self._connected

    @property
    def store(self) -> Dict[str, MqttMessage]:
        return self._store

    def on_message(self, callback: Callable[[MqttMessage], Any]) -> None:
        """Register a callback fired on every incoming MQTT message."""
        self._listeners.append(callback)

    async def start(
        self,
        host: str,
        port: int = 1883,
        username: Optional[str] = None,
        password: Optional[str] = None,
        topics: Optional[List[str]] = None,
        client_id: str = "daily-briefing",
    ) -> None:
        """Connect to the broker and start listening in the background."""
        if not host:
            logger.info("MQTT disabled — no MQTT_HOST configured")
            return

        self._config = dict(
            host=host,
            port=port,
            username=username,
            password=password,
            topics=topics or ["#"],
            client_id=client_id,
        )
        self._task = asyncio.create_task(self._run_loop())
        logger.info("MQTT background task started (broker %s:%d)", host, port)

    async def stop(self) -> None:
        """Disconnect and cancel the background task."""
        if self._task:
            self._task.cancel()
            try:
                await self._task
            except asyncio.CancelledError:
                pass
            self._task = None
        self._connected = False
        logger.info("MQTT service stopped")

    async def publish(
        self,
        topic: str,
        payload: Any,
        retain: bool = False,
    ) -> None:
        """Publish a message to the broker (e.g. for controlling devices)."""
        if not self._client or not self._connected:
            raise RuntimeError("MQTT not connected")
        msg = json.dumps(payload) if not isinstance(payload, (str, bytes)) else payload
        await self._client.publish(topic, msg, retain=retain)
        logger.debug("MQTT published → %s", topic)

    def get_state(self) -> Dict[str, Any]:
        """Return all stored MQTT states for the dashboard API."""
        result: Dict[str, Any] = {}
        for topic, msg in self._store.items():
            result[topic] = {
                "value": msg.payload,
                "timestamp": msg.timestamp,
            }
        return result

    def get_entities(self) -> List[Dict[str, Any]]:
        """Return a flat list of MQTT entities grouped for the frontend."""
        entities: List[Dict[str, Any]] = []
        for topic, msg in self._store.items():
            entities.append({
                "topic": topic,
                "value": msg.payload,
                "timestamp": msg.timestamp,
                "name": _topic_to_name(topic),
                "category": _topic_to_category(topic),
            })
        return entities

    # -- internal ---

    async def _run_loop(self) -> None:
        """Reconnecting event loop."""
        cfg = self._config
        backoff = 1

        while True:
            try:
                async with aiomqtt.Client(
                    hostname=cfg["host"],
                    port=cfg["port"],
                    username=cfg.get("username"),
                    password=cfg.get("password"),
                    identifier=cfg["client_id"],
                ) as client:
                    self._client = client
                    self._connected = True
                    backoff = 1
                    logger.info(
                        "MQTT connected to %s:%d — subscribing to %d topic(s)",
                        cfg["host"],
                        cfg["port"],
                        len(cfg["topics"]),
                    )

                    for t in cfg["topics"]:
                        await client.subscribe(t)

                    async for message in client.messages:
                        await self._handle_message(message)

            except aiomqtt.MqttError as exc:
                self._connected = False
                self._client = None
                logger.warning(
                    "MQTT connection lost (%s) — reconnecting in %ds",
                    exc,
                    backoff,
                )
                await asyncio.sleep(backoff)
                backoff = min(backoff * 2, 60)

            except asyncio.CancelledError:
                self._connected = False
                self._client = None
                break

            except Exception:
                self._connected = False
                self._client = None
                logger.exception("Unexpected MQTT error — reconnecting in %ds", backoff)
                await asyncio.sleep(backoff)
                backoff = min(backoff * 2, 60)

    async def _handle_message(self, message: aiomqtt.Message) -> None:
        topic = str(message.topic)
        raw = message.payload

        # Try JSON decode
        if isinstance(raw, (bytes, bytearray)):
            raw = raw.decode("utf-8", errors="replace")
        try:
            payload = json.loads(raw)
        except (json.JSONDecodeError, TypeError):
            payload = raw

        msg = MqttMessage(topic=topic, payload=payload)
        self._store[topic] = msg

        # Notify listeners
        for cb in self._listeners:
            try:
                result = cb(msg)
                if asyncio.iscoroutine(result):
                    await result
            except Exception:
                logger.exception("MQTT listener error on topic %s", topic)


def _topic_to_name(topic: str) -> str:
    """Derive a human-readable name from the MQTT topic."""
    parts = topic.rstrip("/").split("/")
    return parts[-1].replace("_", " ").replace("-", " ").title() if parts else topic


def _topic_to_category(topic: str) -> str:
    """Derive a category from the first topic segment."""
    parts = topic.strip("/").split("/")
    if len(parts) >= 2:
        return parts[0]
    return "other"


# Singleton
mqtt_service = MqttService()