"""
EventBus service for Redis Pub/Sub communication.

This module provides a centralized event bus for publishing and subscribing to
events across the Syndarix platform. It uses Redis Pub/Sub for real-time
message delivery between services, agents, and the frontend.

Architecture:
- Publishers emit events to project/agent-specific Redis channels
- SSE endpoints subscribe to channels and stream events to clients
- Events include metadata for reconnection support (Last-Event-ID)
- Events are typed with the EventType enum for consistency

Usage:
    # Publishing events
    event_bus = EventBus()
    await event_bus.connect()

    event = event_bus.create_event(
        event_type=EventType.AGENT_MESSAGE,
        project_id=project_id,
        actor_type="agent",
        payload={"message": "Processing..."}
    )
    await event_bus.publish(event_bus.get_project_channel(project_id), event)

    # Subscribing to events
    async for event in event_bus.subscribe(["project:123", "agent:456"]):
        handle_event(event)

    # Cleanup
    await event_bus.disconnect()
"""

import asyncio
import json
import logging
from collections.abc import AsyncGenerator, AsyncIterator
from contextlib import asynccontextmanager
from datetime import UTC, datetime
from typing import Any
from uuid import UUID, uuid4

import redis.asyncio as redis
from pydantic import ValidationError

from app.core.config import settings
from app.schemas.events import ActorType, Event, EventType

logger = logging.getLogger(__name__)


class EventBusError(Exception):
    """Base exception for EventBus errors."""


class EventBusConnectionError(EventBusError):
    """Raised when connection to Redis fails."""


class EventBusPublishError(EventBusError):
    """Raised when publishing an event fails."""


class EventBusSubscriptionError(EventBusError):
    """Raised when subscribing to channels fails."""


class EventBus:
    """
    EventBus for Redis Pub/Sub communication.

    Provides methods to publish events to channels and subscribe to events
    from multiple channels. Handles connection management, serialization,
    and error recovery.

    This class provides:
    - Event publishing to project/agent-specific channels
    - Subscription management for SSE endpoints
    - Reconnection support via event IDs (Last-Event-ID)
    - Keepalive messages for connection health
    - Type-safe event creation with the Event schema

    Attributes:
        redis_url: Redis connection URL
        redis_client: Async Redis client instance
        pubsub: Redis PubSub instance for subscriptions
    """

    # Channel prefixes for different entity types
    PROJECT_CHANNEL_PREFIX = "project"
    AGENT_CHANNEL_PREFIX = "agent"
    USER_CHANNEL_PREFIX = "user"
    GLOBAL_CHANNEL = "syndarix:global"

    def __init__(self, redis_url: str | None = None) -> None:
        """
        Initialize the EventBus.

        Args:
            redis_url: Redis connection URL. Defaults to settings.REDIS_URL.
        """
        self.redis_url = redis_url or settings.REDIS_URL
        self._redis_client: redis.Redis | None = None
        self._pubsub: redis.client.PubSub | None = None
        self._connected = False

    @property
    def redis_client(self) -> redis.Redis:
        """Get the Redis client, raising if not connected."""
        if self._redis_client is None:
            raise EventBusConnectionError(
                "EventBus not connected. Call connect() first."
            )
        return self._redis_client

    @property
    def pubsub(self) -> redis.client.PubSub:
        """Get the PubSub instance, raising if not connected."""
        if self._pubsub is None:
            raise EventBusConnectionError(
                "EventBus not connected. Call connect() first."
            )
        return self._pubsub

    @property
    def is_connected(self) -> bool:
        """Check if the EventBus is connected to Redis."""
        return self._connected and self._redis_client is not None

    async def connect(self) -> None:
        """
        Connect to Redis and initialize the PubSub client.

        Raises:
            EventBusConnectionError: If connection to Redis fails.
        """
        if self._connected:
            logger.debug("EventBus already connected")
            return

        try:
            self._redis_client = redis.from_url(
                self.redis_url,
                encoding="utf-8",
                decode_responses=True,
            )
            # Test connection - ping() returns a coroutine for async Redis
            ping_result = self._redis_client.ping()
            if hasattr(ping_result, "__await__"):
                await ping_result
            self._pubsub = self._redis_client.pubsub()
            self._connected = True
            logger.info("EventBus connected to Redis")
        except redis.ConnectionError as e:
            logger.error(f"Failed to connect to Redis: {e}", exc_info=True)
            raise EventBusConnectionError(f"Failed to connect to Redis: {e}") from e
        except redis.RedisError as e:
            logger.error(f"Redis error during connection: {e}", exc_info=True)
            raise EventBusConnectionError(f"Redis error: {e}") from e

    async def disconnect(self) -> None:
        """
        Disconnect from Redis and cleanup resources.
        """
        if self._pubsub:
            try:
                await self._pubsub.unsubscribe()
                await self._pubsub.close()
            except redis.RedisError as e:
                logger.warning(f"Error closing PubSub: {e}")
            finally:
                self._pubsub = None

        if self._redis_client:
            try:
                await self._redis_client.aclose()
            except redis.RedisError as e:
                logger.warning(f"Error closing Redis client: {e}")
            finally:
                self._redis_client = None

        self._connected = False
        logger.info("EventBus disconnected from Redis")

    @asynccontextmanager
    async def connection(self) -> AsyncIterator["EventBus"]:
        """
        Context manager for automatic connection handling.

        Usage:
            async with event_bus.connection() as bus:
                await bus.publish(channel, event)
        """
        await self.connect()
        try:
            yield self
        finally:
            await self.disconnect()

    def get_project_channel(self, project_id: UUID | str) -> str:
        """
        Get the channel name for a project.

        Args:
            project_id: The project UUID or string

        Returns:
            Channel name string in format "project:{uuid}"
        """
        return f"{self.PROJECT_CHANNEL_PREFIX}:{project_id}"

    def get_agent_channel(self, agent_id: UUID | str) -> str:
        """
        Get the channel name for an agent instance.

        Args:
            agent_id: The agent instance UUID or string

        Returns:
            Channel name string in format "agent:{uuid}"
        """
        return f"{self.AGENT_CHANNEL_PREFIX}:{agent_id}"

    def get_user_channel(self, user_id: UUID | str) -> str:
        """
        Get the channel name for a user (personal notifications).

        Args:
            user_id: The user UUID or string

        Returns:
            Channel name string in format "user:{uuid}"
        """
        return f"{self.USER_CHANNEL_PREFIX}:{user_id}"

    @staticmethod
    def create_event(
        event_type: EventType,
        project_id: UUID,
        actor_type: ActorType,
        payload: dict | None = None,
        actor_id: UUID | None = None,
        event_id: str | None = None,
        timestamp: datetime | None = None,
    ) -> Event:
        """
        Factory method to create a new Event.

        Args:
            event_type: The type of event
            project_id: The project this event belongs to
            actor_type: Type of actor ('agent', 'user', or 'system')
            payload: Event-specific payload data
            actor_id: ID of the agent or user who triggered the event
            event_id: Optional custom event ID (UUID string)
            timestamp: Optional custom timestamp (defaults to now UTC)

        Returns:
            A new Event instance
        """
        return Event(
            id=event_id or str(uuid4()),
            type=event_type,
            timestamp=timestamp or datetime.now(UTC),
            project_id=project_id,
            actor_id=actor_id,
            actor_type=actor_type,
            payload=payload or {},
        )

    def _serialize_event(self, event: Event) -> str:
        """
        Serialize an event to JSON string.

        Args:
            event: The Event to serialize

        Returns:
            JSON string representation of the event
        """
        return event.model_dump_json()

    def _deserialize_event(self, data: str) -> Event:
        """
        Deserialize a JSON string to an Event.

        Args:
            data: JSON string to deserialize

        Returns:
            Deserialized Event instance

        Raises:
            ValidationError: If the data doesn't match the Event schema
        """
        return Event.model_validate_json(data)

    async def publish(self, channel: str, event: Event) -> int:
        """
        Publish an event to a channel.

        Args:
            channel: The channel name to publish to
            event: The Event to publish

        Returns:
            Number of subscribers that received the message

        Raises:
            EventBusConnectionError: If not connected to Redis
            EventBusPublishError: If publishing fails
        """
        if not self.is_connected:
            raise EventBusConnectionError("EventBus not connected")

        try:
            message = self._serialize_event(event)
            subscriber_count = await self.redis_client.publish(channel, message)
            logger.debug(
                f"Published event {event.type} to {channel} "
                f"(received by {subscriber_count} subscribers)"
            )
            return subscriber_count
        except redis.RedisError as e:
            logger.error(f"Failed to publish event to {channel}: {e}", exc_info=True)
            raise EventBusPublishError(f"Failed to publish event: {e}") from e

    async def publish_to_project(self, event: Event) -> int:
        """
        Publish an event to the project's channel.

        Convenience method that publishes to the project channel based on
        the event's project_id.

        Args:
            event: The Event to publish (must have project_id set)

        Returns:
            Number of subscribers that received the message
        """
        channel = self.get_project_channel(event.project_id)
        return await self.publish(channel, event)

    async def publish_multi(self, channels: list[str], event: Event) -> dict[str, int]:
        """
        Publish an event to multiple channels.

        Args:
            channels: List of channel names to publish to
            event: The Event to publish

        Returns:
            Dictionary mapping channel names to subscriber counts
        """
        results = {}
        for channel in channels:
            try:
                results[channel] = await self.publish(channel, event)
            except EventBusPublishError as e:
                logger.warning(f"Failed to publish to {channel}: {e}")
                results[channel] = 0
        return results

    async def subscribe(
        self, channels: list[str], *, max_wait: float | None = None
    ) -> AsyncIterator[Event]:
        """
        Subscribe to one or more channels and yield events.

        This is an async generator that yields Event objects as they arrive.
        Use max_wait to limit how long to wait for messages.

        Args:
            channels: List of channel names to subscribe to
            max_wait: Optional maximum wait time in seconds for each message.
                      If None, waits indefinitely.

        Yields:
            Event objects received from subscribed channels

        Raises:
            EventBusConnectionError: If not connected to Redis
            EventBusSubscriptionError: If subscription fails

        Example:
            async for event in event_bus.subscribe(["project:123"], max_wait=30):
                print(f"Received: {event.type}")
        """
        if not self.is_connected:
            raise EventBusConnectionError("EventBus not connected")

        # Create a new pubsub for this subscription
        subscription_pubsub = self.redis_client.pubsub()

        try:
            await subscription_pubsub.subscribe(*channels)
            logger.info(f"Subscribed to channels: {channels}")
        except redis.RedisError as e:
            logger.error(f"Failed to subscribe to channels: {e}", exc_info=True)
            await subscription_pubsub.close()
            raise EventBusSubscriptionError(f"Failed to subscribe: {e}") from e

        try:
            while True:
                try:
                    if max_wait is not None:
                        async with asyncio.timeout(max_wait):
                            message = await subscription_pubsub.get_message(
                                ignore_subscribe_messages=True, timeout=1.0
                            )
                    else:
                        message = await subscription_pubsub.get_message(
                            ignore_subscribe_messages=True, timeout=1.0
                        )
                except TimeoutError:
                    # Timeout reached, stop iteration
                    return

                if message is None:
                    continue

                if message["type"] == "message":
                    try:
                        event = self._deserialize_event(message["data"])
                        yield event
                    except ValidationError as e:
                        logger.warning(
                            f"Invalid event data received: {e}",
                            extra={"channel": message.get("channel")},
                        )
                        continue
                    except json.JSONDecodeError as e:
                        logger.warning(
                            f"Failed to decode event JSON: {e}",
                            extra={"channel": message.get("channel")},
                        )
                        continue
        finally:
            try:
                await subscription_pubsub.unsubscribe(*channels)
                await subscription_pubsub.close()
                logger.debug(f"Unsubscribed from channels: {channels}")
            except redis.RedisError as e:
                logger.warning(f"Error unsubscribing from channels: {e}")

    async def subscribe_sse(
        self,
        project_id: str | UUID,
        last_event_id: str | None = None,
        keepalive_interval: int = 30,
    ) -> AsyncGenerator[str, None]:
        """
        Subscribe to events for a project in SSE format.

        This is an async generator that yields SSE-formatted event strings.
        It includes keepalive messages at the specified interval.

        Args:
            project_id: The project to subscribe to
            last_event_id: Optional last received event ID for reconnection
            keepalive_interval: Seconds between keepalive messages (default 30)

        Yields:
            SSE-formatted event strings (ready to send to client)
        """
        if not self.is_connected:
            raise EventBusConnectionError("EventBus not connected")

        project_id_str = str(project_id)
        channel = self.get_project_channel(project_id_str)

        subscription_pubsub = self.redis_client.pubsub()
        await subscription_pubsub.subscribe(channel)

        logger.info(
            f"Subscribed to SSE events for project {project_id_str} "
            f"(last_event_id={last_event_id})"
        )

        try:
            while True:
                try:
                    # Wait for messages with a timeout for keepalive
                    message = await asyncio.wait_for(
                        subscription_pubsub.get_message(ignore_subscribe_messages=True),
                        timeout=keepalive_interval,
                    )

                    if message is not None and message["type"] == "message":
                        event_data = message["data"]

                        # If reconnecting, check if we should skip this event
                        if last_event_id:
                            try:
                                event_dict = json.loads(event_data)
                                if event_dict.get("id") == last_event_id:
                                    # Found the last event, start yielding from next
                                    last_event_id = None
                                    continue
                            except json.JSONDecodeError:
                                pass

                        yield event_data

                except TimeoutError:
                    # Send keepalive comment
                    yield ""  # Empty string signals keepalive

        except asyncio.CancelledError:
            logger.info(f"SSE subscription cancelled for project {project_id_str}")
            raise
        finally:
            await subscription_pubsub.unsubscribe(channel)
            await subscription_pubsub.close()
            logger.info(f"Unsubscribed SSE from project {project_id_str}")

    async def subscribe_with_callback(
        self,
        channels: list[str],
        callback: Any,  # Callable[[Event], Awaitable[None]]
        stop_event: asyncio.Event | None = None,
    ) -> None:
        """
        Subscribe to channels and process events with a callback.

        This method runs until stop_event is set or an unrecoverable error occurs.

        Args:
            channels: List of channel names to subscribe to
            callback: Async function to call for each event
            stop_event: Optional asyncio.Event to signal stop

        Example:
            async def handle_event(event: Event):
                print(f"Handling: {event.type}")

            stop = asyncio.Event()
            asyncio.create_task(
                event_bus.subscribe_with_callback(["project:123"], handle_event, stop)
            )
            # Later...
            stop.set()
        """
        if stop_event is None:
            stop_event = asyncio.Event()

        try:
            async for event in self.subscribe(channels):
                if stop_event.is_set():
                    break
                try:
                    await callback(event)
                except Exception as e:
                    logger.error(f"Error in event callback: {e}", exc_info=True)
        except EventBusSubscriptionError:
            raise
        except Exception as e:
            logger.error(f"Unexpected error in subscription loop: {e}", exc_info=True)
            raise


# Singleton instance for application-wide use
_event_bus: EventBus | None = None


def get_event_bus() -> EventBus:
    """
    Get the singleton EventBus instance.

    Creates a new instance if one doesn't exist. Note that you still need
    to call connect() before using the EventBus.

    Returns:
        The singleton EventBus instance
    """
    global _event_bus
    if _event_bus is None:
        _event_bus = EventBus()
    return _event_bus


async def get_connected_event_bus() -> EventBus:
    """
    Get a connected EventBus instance.

    Ensures the EventBus is connected before returning. For use in
    FastAPI dependency injection.

    Returns:
        A connected EventBus instance

    Raises:
        EventBusConnectionError: If connection fails
    """
    event_bus = get_event_bus()
    if not event_bus.is_connected:
        await event_bus.connect()
    return event_bus


async def close_event_bus() -> None:
    """
    Close the global EventBus instance.

    Should be called during application shutdown.
    """
    global _event_bus
    if _event_bus is not None:
        await _event_bus.disconnect()
        _event_bus = None