import asyncio
import logging

logger = logging.getLogger("qkernel.event_bus")


class EventBus:
    def __init__(self):
        self._subscribers: dict[str, list] = {}

    def subscribe(self, event_type: str, handler) -> None:
        if event_type not in self._subscribers:
            self._subscribers[event_type] = []
        self._subscribers[event_type].append(handler)

    def unsubscribe(self, event_type: str, handler) -> None:
        handlers = self._subscribers.get(event_type, [])
        if handler in handlers:
            handlers.remove(handler)

    async def publish(self, event_type: str, data: dict) -> None:
        handlers = self._subscribers.get(event_type, [])
        if not handlers:
            return
        logger.debug("Publishing %s to %d handler(s)", event_type, len(handlers))
        results = await asyncio.gather(
            *[handler(data) for handler in handlers],
            return_exceptions=True,
        )
        for i, r in enumerate(results):
            if isinstance(r, Exception):
                logger.error("Handler %d failed on %s: %s", i, event_type, r)