import asyncio
from typing import Any


class EventBus:
    """In-process pub-sub for server-sent events.

    One asyncio.Queue per subscriber. publish() fans out to all subscribers.
    A single dashboard client is expected; no external broker needed.

    This is intentionally feature-agnostic: voice, timers, alerts, and any
    future server-originated event all share one instance (see `event_bus`
    below) so the frontend can consume them on a single typed event stream.
    """

    def __init__(self) -> None:
        self._subscribers: list[asyncio.Queue[tuple[str, dict[str, Any]]]] = []

    def subscribe(self) -> asyncio.Queue[tuple[str, dict[str, Any]]]:
        q: asyncio.Queue[tuple[str, dict[str, Any]]] = asyncio.Queue(maxsize=64)
        self._subscribers.append(q)
        return q

    def unsubscribe(self, q: asyncio.Queue[tuple[str, dict[str, Any]]]) -> None:
        if q in self._subscribers:
            self._subscribers.remove(q)

    async def publish(self, event_type: str, payload: dict[str, Any]) -> None:
        for q in list(self._subscribers):
            try:
                q.put_nowait((event_type, payload))
            except asyncio.QueueFull:
                # Slow subscriber: drop oldest, then add. SSE clients reconnect.
                try:
                    q.get_nowait()
                except asyncio.QueueEmpty:
                    pass
                q.put_nowait((event_type, payload))


# Shared app-level singleton. Import this everywhere that publishes or
# subscribes — do NOT construct a second EventBus in app code, or publishers
# and the SSE endpoint will be wired to different fan-out lists.
event_bus = EventBus()