# app/api/endpoints/events.py — SSE stream for node status transitions
#
# Clients connect to GET /api/chains/{chain_id}/events and receive
# server-sent events whenever a node in that chain changes status.
#
# Event format:
#   event: node-status
#   data: {"node_id": "...", "status": "generating"|"ready"|"error", ...}
from __future__ import annotations

import asyncio
import json
import logging

from fastapi import APIRouter, Depends
from sse_starlette.sse import EventSourceResponse

from app.api.deps import get_conn
from app.api.events_store import subscribe, unsubscribe

logger = logging.getLogger(__name__)
router = APIRouter(prefix="/api/chains", tags=["events"])

_KEEPALIVE_S = 15  # send a comment ping every N seconds to keep the connection alive


@router.get("/{chain_id}/events")
async def chain_events(chain_id: str, conn=Depends(get_conn)) -> EventSourceResponse:
    """
    SSE stream for node status transitions in a chain.

    Emits 'node-status' events. Closes when the client disconnects.
    """
    q = subscribe(chain_id)

    async def generator():
        try:
            while True:
                try:
                    event = await asyncio.wait_for(q.get(), timeout=_KEEPALIVE_S)
                    yield {
                        "event": "node-status",
                        "data": json.dumps(event),
                    }
                except asyncio.TimeoutError:
                    # Send keepalive comment to prevent proxy/browser timeout
                    yield {"comment": "keepalive"}
        except asyncio.CancelledError:
            pass
        finally:
            unsubscribe(chain_id, q)
            logger.debug("SSE client disconnected from chain %s", chain_id)

    return EventSourceResponse(generator())