"""Redis Pub/Sub service for cross-process notification broadcasting."""

import asyncio
import json
import logging
import uuid
from datetime import datetime
from typing import Optional, Callable, Any
import redis.asyncio as aioredis

from app.core.config import settings

logger = logging.getLogger(__name__)

# Redis retry configuration
MAX_REDIS_RETRIES = 3
REDIS_RETRY_DELAY = 0.5  # seconds (base delay for exponential backoff)

# Global async Redis client for pub/sub
_pubsub_redis: Optional[aioredis.Redis] = None


def get_channel_name(user_id: str) -> str:
    """Get the Redis channel name for a user's notifications."""
    return f"notifications:{user_id}"


def get_project_channel_name(project_id: str) -> str:
    """Get the Redis channel name for project task events."""
    return f"project:{project_id}:tasks"


async def get_pubsub_redis() -> aioredis.Redis:
    """Get or create the async Redis client for pub/sub."""
    global _pubsub_redis
    if _pubsub_redis is None:
        _pubsub_redis = aioredis.from_url(
            settings.REDIS_URL,
            encoding="utf-8",
            decode_responses=True,
        )
    return _pubsub_redis


async def close_pubsub_redis() -> None:
    """Close the async Redis client."""
    global _pubsub_redis
    if _pubsub_redis is not None:
        await _pubsub_redis.close()
        _pubsub_redis = None


async def publish_notification(user_id: str, notification: dict) -> bool:
    """
    Publish a notification to a user's channel.

    Args:
        user_id: The user ID to send the notification to
        notification: The notification data (will be JSON serialized)

    Returns:
        True if published successfully, False otherwise
    """
    try:
        redis_client = await get_pubsub_redis()
        channel = get_channel_name(user_id)
        message = json.dumps(notification, default=str)
        await redis_client.publish(channel, message)
        logger.debug(f"Published notification to channel {channel}")
        return True
    except Exception as e:
        logger.error(f"Failed to publish notification: {e}")
        return False


class NotificationSubscriber:
    """
    Subscriber for user notification channels.
    Used by WebSocket connections to receive real-time updates.
    """

    def __init__(self, user_id: str):
        self.user_id = user_id
        self.channel = get_channel_name(user_id)
        self.pubsub: Optional[aioredis.client.PubSub] = None
        self._running = False

    async def start(self) -> None:
        """Start subscribing to the user's notification channel."""
        redis_client = await get_pubsub_redis()
        self.pubsub = redis_client.pubsub()
        await self.pubsub.subscribe(self.channel)
        self._running = True
        logger.debug(f"Subscribed to channel {self.channel}")

    async def stop(self) -> None:
        """Stop subscribing and clean up."""
        self._running = False
        if self.pubsub:
            await self.pubsub.unsubscribe(self.channel)
            await self.pubsub.close()
            self.pubsub = None
            logger.debug(f"Unsubscribed from channel {self.channel}")

    async def listen(self, callback: Callable[[dict], Any]) -> None:
        """
        Listen for messages and call the callback for each notification.

        Args:
            callback: Async function to call with each notification dict
        """
        if not self.pubsub:
            raise RuntimeError("Subscriber not started. Call start() first.")

        try:
            async for message in self.pubsub.listen():
                if not self._running:
                    break

                if message["type"] == "message":
                    try:
                        data = json.loads(message["data"])
                        await callback(data)
                    except json.JSONDecodeError:
                        logger.warning(f"Invalid JSON in notification: {message['data']}")
                    except Exception as e:
                        logger.error(f"Error processing notification: {e}")
        except Exception as e:
            if self._running:
                logger.error(f"Error in notification listener: {e}")

    @property
    def is_running(self) -> bool:
        return self._running


async def _reset_pubsub_redis() -> None:
    """Reset the Redis connection on failure."""
    global _pubsub_redis
    if _pubsub_redis is not None:
        try:
            await _pubsub_redis.close()
        except Exception:
            pass
        _pubsub_redis = None


async def publish_task_event(
    project_id: str,
    event_type: str,
    task_data: dict,
    triggered_by: str
) -> bool:
    """
    Publish a task event to a project's channel with retry logic.

    Args:
        project_id: The project ID
        event_type: Event type (task_created, task_updated, task_status_changed, task_deleted, task_assigned)
        task_data: The task data to include in the event
        triggered_by: User ID who triggered this event

    Returns:
        True if published successfully, False otherwise
    """
    channel = get_project_channel_name(project_id)
    message = json.dumps({
        "type": event_type,
        "event_id": str(uuid.uuid4()),  # Unique event ID for multi-tab deduplication
        "data": task_data,
        "triggered_by": triggered_by,
        "timestamp": datetime.utcnow().isoformat(),
    }, default=str)

    for attempt in range(MAX_REDIS_RETRIES):
        try:
            redis_client = await get_pubsub_redis()
            # Test connection with ping before publishing
            await redis_client.ping()
            await redis_client.publish(channel, message)
            logger.debug(f"Published task event '{event_type}' to channel {channel}")
            return True
        except Exception as e:
            logger.warning(f"Redis publish attempt {attempt + 1}/{MAX_REDIS_RETRIES} failed: {e}")
            if attempt < MAX_REDIS_RETRIES - 1:
                # Exponential backoff
                await asyncio.sleep(REDIS_RETRY_DELAY * (attempt + 1))
                # Reset connection on failure
                await _reset_pubsub_redis()
            else:
                logger.error(f"Failed to publish task event '{event_type}' after {MAX_REDIS_RETRIES} attempts")
                return False
    return False


class ProjectTaskSubscriber:
    """
    Subscriber for project task events via Redis Pub/Sub.
    Used by WebSocket connections to receive real-time task updates.
    Includes automatic reconnection handling.
    """

    def __init__(self, project_id: str):
        self.project_id = project_id
        self.channel = get_project_channel_name(project_id)
        self.pubsub: Optional[aioredis.client.PubSub] = None
        self._running = False
        self._reconnect_attempts = 0

    async def start(self) -> None:
        """Start subscribing to the project's task channel with retry logic."""
        for attempt in range(MAX_REDIS_RETRIES):
            try:
                redis_client = await get_pubsub_redis()
                # Test connection health
                await redis_client.ping()
                self.pubsub = redis_client.pubsub()
                await self.pubsub.subscribe(self.channel)
                self._running = True
                self._reconnect_attempts = 0
                logger.debug(f"Subscribed to project task channel {self.channel}")
                return
            except Exception as e:
                logger.warning(f"Redis subscribe attempt {attempt + 1}/{MAX_REDIS_RETRIES} failed: {e}")
                if attempt < MAX_REDIS_RETRIES - 1:
                    await asyncio.sleep(REDIS_RETRY_DELAY * (attempt + 1))
                    await _reset_pubsub_redis()
                else:
                    logger.error(f"Failed to subscribe to channel {self.channel} after {MAX_REDIS_RETRIES} attempts")
                    raise

    async def _reconnect(self) -> bool:
        """Attempt to reconnect to Redis and resubscribe."""
        self._reconnect_attempts += 1
        if self._reconnect_attempts > MAX_REDIS_RETRIES:
            logger.error(f"Max reconnection attempts reached for channel {self.channel}")
            return False

        logger.info(f"Attempting to reconnect to Redis (attempt {self._reconnect_attempts}/{MAX_REDIS_RETRIES})")

        # Clean up old pubsub
        if self.pubsub:
            try:
                await self.pubsub.close()
            except Exception:
                pass
            self.pubsub = None

        # Reset global connection
        await _reset_pubsub_redis()

        # Wait with exponential backoff
        await asyncio.sleep(REDIS_RETRY_DELAY * self._reconnect_attempts)

        try:
            redis_client = await get_pubsub_redis()
            await redis_client.ping()
            self.pubsub = redis_client.pubsub()
            await self.pubsub.subscribe(self.channel)
            self._reconnect_attempts = 0
            logger.info(f"Successfully reconnected to channel {self.channel}")
            return True
        except Exception as e:
            logger.warning(f"Reconnection attempt failed: {e}")
            return False

    async def stop(self) -> None:
        """Stop subscribing and clean up."""
        self._running = False
        if self.pubsub:
            try:
                await self.pubsub.unsubscribe(self.channel)
                await self.pubsub.close()
            except Exception as e:
                logger.warning(f"Error during pubsub cleanup: {e}")
            self.pubsub = None
            logger.debug(f"Unsubscribed from project task channel {self.channel}")

    async def listen(self, callback: Callable[[dict], Any]) -> None:
        """
        Listen for task events and call the callback for each event.
        Includes automatic reconnection on connection failures.

        Args:
            callback: Async function to call with each task event dict.
                      The dict contains: type, data, triggered_by
        """
        if not self.pubsub:
            raise RuntimeError("Subscriber not started. Call start() first.")

        while self._running:
            try:
                async for message in self.pubsub.listen():
                    if not self._running:
                        break

                    if message["type"] == "message":
                        try:
                            data = json.loads(message["data"])
                            await callback(data)
                        except json.JSONDecodeError:
                            logger.warning(f"Invalid JSON in task event: {message['data']}")
                        except Exception as e:
                            logger.error(f"Error processing task event: {e}")
            except Exception as e:
                if not self._running:
                    break
                logger.warning(f"Redis connection error in task listener: {e}")
                # Attempt to reconnect
                if await self._reconnect():
                    continue  # Resume listening after successful reconnection
                else:
                    logger.error(f"Failed to recover connection for channel {self.channel}")
                    break

    @property
    def is_running(self) -> bool:
        return self._running