"""`GET /api/events`: the server-sent event stream (session required; locked sessions allowed)."""

from __future__ import annotations

from fastapi import APIRouter, Query, Request
from fastapi.responses import StreamingResponse
from starlette.concurrency import run_in_threadpool

from ..auth.groups import SCREENS
from ..events import EventHub, stream
from .deps import resolve_standalone, settings_of

router = APIRouter(prefix="/api", tags=["events"])

SSE_HEADERS = {"Cache-Control": "no-cache", "X-Accel-Buffering": "no", "Connection": "keep-alive"}


@router.get("/events")
async def events(
    request: Request,
    screen: str | None = Query(None, max_length=32),
    packet_id: int | None = Query(None, ge=1, le=2**62),
) -> StreamingResponse:
    """The event stream. `packet_id` is the packet the page has open; presence carries it, so the packet page can
    show who else is looking at the same packet. The client reopens the stream when the open packet changes."""
    # The session check runs on its own pooled connection, returned before the stream starts
    p = await run_in_threadpool(resolve_standalone, request)
    hub: EventHub = request.app.state.events
    sub = hub.subscribe(
        session_id=p.session_id,
        user_id=p.user_id,
        display_name=p.user["display_name"],
        screen=screen if screen in SCREENS and screen in p.screens else None,
        packet_id=packet_id,
    )
    hello = {"session_id": str(p.session_id), "build": settings_of(request).ps_build}
    return StreamingResponse(
        stream(hub, sub, hello=hello, is_disconnected=request.is_disconnected),
        media_type="text/event-stream",
        headers=SSE_HEADERS,
    )