from collections import defaultdict
from typing import Callable


class EventBus:
    """Observer 패턴 기반 이벤트 버스."""

    def __init__(self):
        self._handlers: dict[str, list[Callable]] = defaultdict(list)

    def subscribe(self, event: str, handler: Callable) -> None:
        self._handlers[event].append(handler)

    def unsubscribe(self, event: str, handler: Callable) -> None:
        self._handlers[event].remove(handler)

    def publish(self, event: str, *args, **kwargs) -> None:
        for handler in self._handlers[event]:
            handler(*args, **kwargs)