export class EventBus<T extends Record<string, unknown[]>> {
  private handlers: Map<keyof T, Set<(...args: T[keyof T]) => void>> = new Map();

  on<K extends keyof T>(event: K, handler: (...args: T[K]) => void): void {
    let eventHandlers = this.handlers.get(event) as Set<(...args: T[K]) => void> | undefined;
    if (!eventHandlers) {
      eventHandlers = new Set<(...args: T[K]) => void>();
      this.handlers.set(event, eventHandlers as Set<(...args: T[keyof T]) => void>);
    }
    eventHandlers.add(handler);
  }

  off<K extends keyof T>(event: K, handler: (...args: T[K]) => void): void {
    const eventHandlers = this.handlers.get(event) as Set<(...args: T[K]) => void> | undefined;
    if (!eventHandlers) {
      return;
    }

    eventHandlers.delete(handler);
    if (eventHandlers.size === 0) {
      this.handlers.delete(event);
    }
  }

  emit<K extends keyof T>(event: K, ...args: T[K]): void {
    const eventHandlers = this.handlers.get(event) as Set<(...args: T[K]) => void> | undefined;
    if (!eventHandlers) {
      return;
    }

    for (const handler of [...eventHandlers]) {
      handler(...args);
    }
  }
}