// eslint-disable-next-line @typescript-eslint/no-restricted-types
export type CallbackFn = Function;
export type UnregisterFn = () => void;

export interface EventBus {
  on: (eventName: string, fn: CallbackFn) => UnregisterFn;
  off: (eventName: string, fn: CallbackFn) => void;
  emit: <T = Event>(eventName: string, event?: T) => void;
}

export function createEventBus(): EventBus {
  const handlers = new Map<string, CallbackFn[]>();

  function off(eventName: string, fn: CallbackFn) {
    const eventFns = handlers.get(eventName);

    if (eventFns) {
      eventFns.splice(eventFns.indexOf(fn) >>> 0, 1);
    }
  }

  function on(eventName: string, fn: CallbackFn): UnregisterFn {
    let eventFns = handlers.get(eventName);

    if (!eventFns) {
      eventFns = [fn];
    } else {
      eventFns.push(fn);
    }

    handlers.set(eventName, eventFns);

    return () => off(eventName, fn);
  }

  function emit<T = Event>(eventName: string, event?: T) {
    const eventFns = handlers.get(eventName);

    if (eventFns) {
      eventFns.slice().forEach(async (handler) => {
        await handler(event);
      });
    }
  }

  return {
    on,
    off,
    emit,
  };
}