import asyncio
import contextlib
from collections import defaultdict
from datetime import datetime, timezone
from uuid import uuid4

from fastapi import WebSocket
from sqlalchemy.ext.asyncio import AsyncSession

from app.chats.repository import list_user_chat_ids
from app.chats.service import ensure_chat_membership
from app.database.session import AsyncSessionLocal
from app.messages.schemas import MessageCreateRequest, MessageRead, MessageStatusUpdateRequest
from app.messages.service import create_chat_message, mark_message_status
from app.realtime.models import ConnectionContext
from app.realtime.presence import mark_user_offline, mark_user_online
from app.realtime.repository import RedisRealtimeRepository
from app.realtime.schemas import ChatEventPayload, MessageStatusPayload, OutgoingRealtimeEvent, SendMessagePayload
from app.users.repository import update_user_last_seen_now


class RealtimeGateway:
    def __init__(self) -> None:
        self._repo = RedisRealtimeRepository()
        self._consume_task: asyncio.Task | None = None
        self._distributed_enabled = False
        self._connections: dict[int, dict[str, ConnectionContext]] = defaultdict(dict)
        self._chat_subscribers: dict[int, set[int]] = defaultdict(set)

    async def start(self) -> None:
        try:
            await self._repo.connect()
            if not self._consume_task:
                self._consume_task = asyncio.create_task(self._repo.consume(self._handle_redis_event))
            self._distributed_enabled = True
        except Exception:
            self._distributed_enabled = False

    async def stop(self) -> None:
        if self._consume_task:
            self._consume_task.cancel()
            with contextlib.suppress(asyncio.CancelledError):
                await self._consume_task
            self._consume_task = None
        await self._repo.close()
        self._distributed_enabled = False

    async def register(self, user_id: int, websocket: WebSocket, user_chat_ids: list[int]) -> str:
        connection_id = str(uuid4())
        self._connections[user_id][connection_id] = ConnectionContext(
            user_id=user_id,
            connection_id=connection_id,
            websocket=websocket,
        )
        for chat_id in user_chat_ids:
            self._chat_subscribers[chat_id].add(user_id)
        became_online = await mark_user_online(user_id)
        if became_online:
            await self._broadcast_presence(user_chat_ids, user_id=user_id, is_online=True, last_seen_at=None)
        await self._send_user_event(
            user_id,
            OutgoingRealtimeEvent(
                event="connect",
                payload={"connection_id": connection_id},
                timestamp=datetime.now(timezone.utc),
            ),
        )
        return connection_id

    async def unregister(self, user_id: int, connection_id: str, user_chat_ids: list[int]) -> None:
        user_connections = self._connections.get(user_id, {})
        user_connections.pop(connection_id, None)
        if not user_connections:
            self._connections.pop(user_id, None)
            for chat_id in user_chat_ids:
                subscribers = self._chat_subscribers.get(chat_id)
                if not subscribers:
                    continue
                subscribers.discard(user_id)
                if not subscribers:
                    self._chat_subscribers.pop(chat_id, None)
            became_offline = await mark_user_offline(user_id)
            await self._persist_last_seen(user_id)
            if became_offline:
                await self._broadcast_presence(
                    user_chat_ids,
                    user_id=user_id,
                    is_online=False,
                    last_seen_at=datetime.now(timezone.utc),
                )

    async def handle_send_message(self, db: AsyncSession, user_id: int, payload: SendMessagePayload) -> None:
        message = await create_chat_message(
            db,
            sender_id=user_id,
            payload=MessageCreateRequest(
                chat_id=payload.chat_id,
                type=payload.type,
                text=payload.text,
                client_message_id=payload.client_message_id or payload.temp_id,
                reply_to_message_id=payload.reply_to_message_id,
            ),
        )
        await self.publish_message_created(
            message=message,
            sender_id=user_id,
            temp_id=payload.temp_id,
            client_message_id=payload.client_message_id,
        )

    async def handle_typing_event(self, db: AsyncSession, user_id: int, payload: ChatEventPayload, event: str) -> None:
        await ensure_chat_membership(db, chat_id=payload.chat_id, user_id=user_id)
        await self._publish_chat_event(
            payload.chat_id,
            event=event,
            payload={"chat_id": payload.chat_id, "user_id": user_id},
        )

    async def handle_message_status(
        self,
        db: AsyncSession,
        user_id: int,
        payload: MessageStatusPayload,
        event: str,
    ) -> dict[str, int]:
        receipt_state = await mark_message_status(
            db,
            user_id=user_id,
            payload=MessageStatusUpdateRequest(chat_id=payload.chat_id, message_id=payload.message_id, status=event),
        )
        await self._publish_chat_event(
            payload.chat_id,
            event=event,
            payload={
                "chat_id": payload.chat_id,
                "message_id": payload.message_id,
                "user_id": user_id,
                "last_delivered_message_id": receipt_state["last_delivered_message_id"],
                "last_read_message_id": receipt_state["last_read_message_id"],
            },
        )
        return receipt_state

    async def load_user_chat_ids(self, db: AsyncSession, user_id: int) -> list[int]:
        return await list_user_chat_ids(db, user_id=user_id)

    def add_chat_subscription(self, *, chat_id: int, user_id: int) -> None:
        self._chat_subscribers[chat_id].add(user_id)

    def remove_chat_subscription(self, *, chat_id: int, user_id: int) -> None:
        subscribers = self._chat_subscribers.get(chat_id)
        if not subscribers:
            return
        subscribers.discard(user_id)
        if not subscribers:
            self._chat_subscribers.pop(chat_id, None)

    async def publish_chat_updated(self, *, chat_id: int) -> None:
        await self._publish_chat_event(
            chat_id,
            event="chat_updated",
            payload={"chat_id": chat_id},
        )

    async def _handle_redis_event(self, channel: str, payload: dict) -> None:
        chat_id = self._extract_chat_id(channel)
        if chat_id is None:
            return
        subscribers = self._chat_subscribers.get(chat_id, set())
        if not subscribers:
            return
        event = OutgoingRealtimeEvent(
            event=payload.get("event", "error"),
            payload=payload.get("payload", {}),
            timestamp=datetime.now(timezone.utc),
        )
        await asyncio.gather(*(self._send_user_event(user_id, event) for user_id in subscribers), return_exceptions=True)

    async def _publish_chat_event(self, chat_id: int, *, event: str, payload: dict) -> None:
        event_payload = {
            "event": event,
            "payload": payload,
            "timestamp": datetime.now(timezone.utc).isoformat(),
        }
        if self._distributed_enabled:
            await self._repo.publish_event(f"chat:{chat_id}", event_payload)
            return
        await self._handle_redis_event(f"chat:{chat_id}", event_payload)

    async def publish_message_created(
        self,
        *,
        message,
        sender_id: int,
        temp_id: str | None = None,
        client_message_id: str | None = None,
    ) -> None:
        message_data = MessageRead.model_validate(message).model_dump(mode="json")
        await self._publish_chat_event(
            message.chat_id,
            event="receive_message",
            payload={
                "chat_id": message.chat_id,
                "message": message_data,
                "temp_id": temp_id,
                "client_message_id": client_message_id,
                "sender_id": sender_id,
            },
        )

    async def _send_user_event(self, user_id: int, event: OutgoingRealtimeEvent) -> None:
        user_connections = self._connections.get(user_id, {})
        if not user_connections:
            return
        disconnected: list[str] = []
        for connection_id, context in user_connections.items():
            try:
                await context.websocket.send_json(event.model_dump(mode="json"))
            except Exception:
                disconnected.append(connection_id)
        for connection_id in disconnected:
            user_connections.pop(connection_id, None)
        if not user_connections:
            self._connections.pop(user_id, None)
            affected_chat_ids: list[int] = []
            for chat_id, subscribers in list(self._chat_subscribers.items()):
                if user_id in subscribers:
                    affected_chat_ids.append(chat_id)
                subscribers.discard(user_id)
                if not subscribers:
                    self._chat_subscribers.pop(chat_id, None)
            became_offline = await mark_user_offline(user_id)
            await self._persist_last_seen(user_id)
            if became_offline:
                await self._broadcast_presence(
                    affected_chat_ids,
                    user_id=user_id,
                    is_online=False,
                    last_seen_at=datetime.now(timezone.utc),
                )

    @staticmethod
    def _extract_chat_id(channel: str) -> int | None:
        if not channel.startswith("chat:"):
            return None
        chat_id = channel.split(":", maxsplit=1)[1]
        if not chat_id.isdigit():
            return None
        return int(chat_id)

    async def _persist_last_seen(self, user_id: int) -> None:
        try:
            async with AsyncSessionLocal() as db:
                await update_user_last_seen_now(db, user_id=user_id)
                await db.commit()
        except Exception:
            return

    async def _broadcast_presence(
        self,
        chat_ids: list[int],
        *,
        user_id: int,
        is_online: bool,
        last_seen_at: datetime | None,
    ) -> None:
        event_name = "user_online" if is_online else "user_offline"
        for chat_id in chat_ids:
            payload = {
                "chat_id": chat_id,
                "user_id": user_id,
                "is_online": is_online,
            }
            if last_seen_at is not None:
                payload["last_seen_at"] = last_seen_at.isoformat()
            await self._publish_chat_event(chat_id, event=event_name, payload=payload)


realtime_gateway = RealtimeGateway()