EventEmitter.ts

export type EventMap = Record<string, unknown>;
export type Arguments<Arg> = Arg extends void ? [] : [Arg];
export type Listener<Arg> = (...args: Arguments<Arg>) => void;

export class EventEmitter<
  Map extends EventMap,
  K extends keyof Map = keyof Map,
> {
  private map: {
    [E in K]?: Set<Listener<Map[E]>>;
  } = {};

  on<E extends K>(event: E, listener: Listener<Map[E]>): this {
    if (!this.map[event]) {
      this.map[event] = new Set();
    }

    this.map[event].add(listener);
    return this;
  }

  off<E extends K>(event: E, listener: Listener<Map[E]>): this {
    if (!this.map[event]) return this;

    this.map[event].delete(listener);

    if (this.map[event].size === 0) {
      delete this.map[event];
    }

    return this;
  }

  protected emit<E extends K>(event: E, ...args: Arguments<Map[E]>): this {
    if (this.map[event]) {
      for (const listener of this.map[event]) {
        listener(...args);
      }
    }

    return this;
  }

  protected dispose(): this {
    this.map = {};
    return this;
  }
}