"""
app/services/event_service.py
Server-Sent Events (SSE) broadcaster.
Maintains a set of subscriber asyncio queues and fans out events to all of them.
"""

from __future__ import annotations

import asyncio
import json
import logging
from datetime import datetime, timezone
from typing import AsyncGenerator

logger = logging.getLogger(__name__)

# All active SSE subscriber queues
_subscribers: set[asyncio.Queue] = set()


def subscribe() -> asyncio.Queue:
    """Register a new SSE subscriber and return its queue."""
    q: asyncio.Queue = asyncio.Queue(maxsize=64)
    _subscribers.add(q)
    logger.debug("SSE subscriber added, total=%d", len(_subscribers))
    return q


def unsubscribe(q: asyncio.Queue) -> None:
    """Remove a subscriber queue."""
    _subscribers.discard(q)
    logger.debug("SSE subscriber removed, total=%d", len(_subscribers))


def broadcast(event_type: str, data: dict) -> None:
    """
    Fan out an event to all current subscribers.
    Safe to call from synchronous code – uses put_nowait and discards slow consumers.
    """
    payload = json.dumps(
        {
            "type": event_type,
            "timestamp": datetime.now(timezone.utc).isoformat(),
            "data": data,
        }
    )
    dead: list[asyncio.Queue] = []
    for q in list(_subscribers):
        try:
            q.put_nowait(payload)
        except asyncio.QueueFull:
            logger.warning("SSE subscriber queue full, dropping event type=%s", event_type)
            dead.append(q)
    for q in dead:
        _subscribers.discard(q)


async def event_generator(q: asyncio.Queue) -> AsyncGenerator[str, None]:
    """
    Async generator that yields SSE-formatted strings from a subscriber queue.
    Yields a keep-alive comment every 15 seconds when idle.
    """
    try:
        while True:
            try:
                payload = await asyncio.wait_for(q.get(), timeout=15.0)
                yield f"data: {payload}\n\n"
            except asyncio.TimeoutError:
                # Keep-alive ping so browsers don't close the connection
                yield ": ping\n\n"
    except asyncio.CancelledError:
        pass
    finally:
        unsubscribe(q)