"""SSE-эндпоинт (ТЗ 3.14): поток событий для SPA.

EventSource фронтенда держит соединение открытым; сервер шлёт события шины
и ping каждые PING_SECONDS секунд (keep-alive, чтобы прокси не рвал поток).
"""

import asyncio
import json
from collections.abc import AsyncIterator
from typing import Any

from fastapi import APIRouter
from starlette.requests import Request
from starlette.responses import StreamingResponse

from app.dependencies import UserDep
from app.realtime import Event, bus

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

# keep-alive: прокси (Vite dev, nginx) закрывают «тихие» соединения
PING_SECONDS = 20.0


def _sse_json(kind: str, data: dict[str, Any] | None = None) -> str:
    payload: dict[str, Any] = {"kind": kind}
    if data:
        payload["data"] = data
    return json.dumps(payload, ensure_ascii=False)


async def _event_source(request: Request, user_id: str) -> AsyncIterator[str]:
    queue = bus.subscribe(user_id)
    try:
        yield f"data: {_sse_json('ready')}\n\n"
        while True:
            if await request.is_disconnected():
                return
            try:
                event: Event = await asyncio.wait_for(queue.get(), timeout=PING_SECONDS)
                payload = _sse_json(event.kind, event.data)
            except TimeoutError:
                payload = _sse_json("ping")
            yield f"data: {payload}\n\n"
    finally:
        bus.unsubscribe(user_id, queue)


@router.get("")
async def events(request: Request, user: UserDep) -> StreamingResponse:
    """SSE-поток: события изменений + ping (keep-alive)."""
    return StreamingResponse(
        _event_source(request, str(user["user_id"])),
        media_type="text/event-stream",
        headers={
            "Cache-Control": "no-cache",
            # nginx в проде не буферизует стрим
            "X-Accel-Buffering": "no",
        },
    )