"""WebSocket endpoint for real-time task progress updates.

Clients connect to ``/api/ws/tasks?token=<jwt>`` and receive live progress
messages published by Celery workers via Redis pub/sub.
"""
import asyncio
import json
import logging
from typing import Any

import jwt
import redis.asyncio as aioredis
from fastapi import APIRouter, WebSocket, WebSocketDisconnect

from api.auth import _verify_authentik_token, _verify_passkey_token, User
from api.config import JWT_ISSUER
from services import task_service

logger = logging.getLogger(__name__)

ws_router = APIRouter()

# Reuse the broker URL for the async Redis client
import os
_BROKER_URL = os.getenv("CELERY_BROKER_URL", "redis://redis:6379/0")


async def _authenticate_ws(token: str) -> User | None:
    """Verify a JWT token using the same logic as api/auth.py."""
    try:
        unverified = jwt.decode(
            token, options={"verify_signature": False, "verify_exp": False}
        )
        issuer = unverified.get("iss", "")
        if issuer == JWT_ISSUER:
            return _verify_passkey_token(token)
        else:
            return await _verify_authentik_token(token)
    except Exception:
        return None


async def _build_task_snapshot(task_id: str) -> dict[str, Any]:
    """Build a snapshot of a task's current status for the init message."""
    return await asyncio.to_thread(_build_task_snapshot_sync, task_id)


def _build_task_snapshot_sync(task_id: str) -> dict[str, Any]:
    """Synchronous helper — runs in a thread to avoid blocking the loop."""
    status = task_service.get_task_status(task_id)
    result: dict[str, Any] = {
        "task_id": status.task_id,
        "status": status.status,
        "progress": status.progress,
        "processed": status.processed,
        "total": status.total,
        "message": status.message,
    }
    if status.result and isinstance(status.result, dict):
        result.update(status.result)
    return result


@ws_router.websocket("/api/ws/tasks")
async def ws_task_progress(websocket: WebSocket) -> None:
    token = websocket.query_params.get("token")
    if not token:
        await websocket.close(code=4001, reason="Missing token")
        return

    user = await _authenticate_ws(token)
    if user is None:
        await websocket.close(code=4003, reason="Invalid token")
        return

    await websocket.accept()

    task_ids = task_service.get_user_tasks(user.email)

    # Subscribe to Redis pub/sub FIRST so no updates are lost while
    # building snapshots.  Messages that arrive between subscribe and
    # the init send are buffered by Redis and forwarded afterwards.
    redis_client = aioredis.from_url(_BROKER_URL, decode_responses=True)
    pubsub = redis_client.pubsub()

    subscribed_channels: set[str] = set()
    for tid in task_ids:
        channel = f"task_progress:{tid}"
        await pubsub.subscribe(channel)
        subscribed_channels.add(channel)

    # Now build snapshots (safe — pub/sub is already active)
    # _build_task_snapshot calls synchronous Celery APIs, so run in a
    # thread to avoid blocking the event loop.
    snapshots = []
    for tid in task_ids:
        try:
            snapshots.append(await asyncio.to_thread(_build_task_snapshot_sync, tid))
        except Exception:
            logger.debug("Failed to build snapshot for task %s", tid, exc_info=True)

    try:
        await websocket.send_json({"type": "init", "tasks": snapshots})
    except Exception:
        await pubsub.unsubscribe(*subscribed_channels)
        await pubsub.close()
        await redis_client.aclose()
        return

    async def _forward_pubsub() -> None:
        """Read from Redis pub/sub and forward to the WebSocket."""
        while True:
            message = await pubsub.get_message(
                ignore_subscribe_messages=True, timeout=1.0
            )
            if message and message["type"] == "message":
                try:
                    data = json.loads(message["data"])
                except (json.JSONDecodeError, ValueError):
                    logger.debug("Malformed pubsub message, skipping")
                    continue
                try:
                    await websocket.send_json({"type": "task_update", **data})
                except Exception:
                    break

    async def _handle_client_messages() -> None:
        """Read messages from the client (subscribe, ping)."""
        while True:
            try:
                raw = await websocket.receive_text()
                msg = json.loads(raw)
            except WebSocketDisconnect:
                raise
            except Exception:
                continue

            msg_type = msg.get("type")
            if msg_type == "subscribe":
                new_task_id = msg.get("task_id")
                if new_task_id:
                    channel = f"task_progress:{new_task_id}"
                    if channel not in subscribed_channels:
                        await pubsub.subscribe(channel)
                        subscribed_channels.add(channel)
                    # Send current snapshot for the new task
                    try:
                        snapshot = await _build_task_snapshot(new_task_id)
                        await websocket.send_json(
                            {"type": "task_update", **snapshot}
                        )
                    except Exception:
                        pass
            elif msg_type == "ping":
                try:
                    await websocket.send_json({"type": "pong"})
                except Exception:
                    break

    try:
        ws_tasks = [
            asyncio.create_task(_forward_pubsub()),
            asyncio.create_task(_handle_client_messages()),
        ]
        done, pending = await asyncio.wait(
            ws_tasks, return_when=asyncio.FIRST_COMPLETED
        )
        for t in pending:
            t.cancel()
        # Log non-trivial errors from the completed task(s)
        for t in done:
            exc = t.exception()
            if exc and not isinstance(exc, (WebSocketDisconnect, asyncio.CancelledError)):
                logger.debug("WS task ended with error: %s", exc)
    except (WebSocketDisconnect, Exception):
        pass
    finally:
        await pubsub.unsubscribe(*subscribed_channels)
        await pubsub.close()
        await redis_client.aclose()