type Listener = (value: any) => void;

type Topics = {
  [name: string]: Listener[];
};

export const createPubSub = () => {
  let topics: Topics = {};
  let destroyed = false;

  const getTopic = (name: string) => {
    if (!topics[name]) {
      topics[name] = [];
    }

    return topics[name];
  };

  return {
    subscribe(topic: string, fn: Listener) {
      const listeners = getTopic(topic);

      listeners.push(fn);

      const unsubscribe = () => {
        const index = listeners.indexOf(fn);

        listeners.splice(index, 1);
      };

      return unsubscribe;
    },

    publish(topic: string, value: any) {
      const listeners = getTopic(topic);
      const currentListeners = listeners.slice();

      currentListeners.forEach((listener) => {
        if (!destroyed) {
          listener(value);
        }
      });
    },

    destroy() {
      topics = {};
      destroyed = true;
    },
  };
};