@thi.ng/csp/pubsub.js

Primitives & operators for Communicating Sequential Processes based on async/await and async iterables

import { illegalArity } from "@thi.ng/errors/illegal-arity";
import { Channel } from "./channel.js";
import { Mult } from "./mult.js";
function pubsub(...args) {
  return new PubSub(...args);
}
class PubSub {
  src;
  fn;
  topics;
  constructor(...args) {
    switch (args.length) {
      case 2:
        this.src = args[0];
        this.fn = args[1];
        break;
      case 1:
        this.src = new Channel();
        this.fn = args[0];
        break;
      default:
        illegalArity(args.length);
    }
    this.topics = {};
    this.process();
  }
  writable() {
    return this.src.writable();
  }
  write(val) {
    return this.src.write(val);
  }
  close() {
    return this.src.close();
  }
  closed() {
    return this.src.closed();
  }
  /**
   * Creates a new topic subscription channel and returns it. Each topic is
   * managed by its own {@link Mult} and can have arbitrary number of
   * subscribers.
   *
   * @param id - topic id
   */
  subscribeTopic(id) {
    let topic = this.topics[id];
    if (!topic) {
      this.topics[id] = topic = new Mult(`${this.src.id}-${id}`);
    }
    return topic.subscribe();
  }
  /**
   * Attempts to remove a subscription channel for given topic `id`. Returns
   * true if successful. If `close` is true (default), the given channel will
   * also be closed (only if unsubscription was successful).
   *
   * @remarks
   * See {@link Mult.subscribe} for reverse op.
   *
   * @param id
   * @param ch
   * @param close
   */
  unsubscribeTopic(id, ch, close = true) {
    const topic = this.topics[id];
    return topic?.unsubscribe(ch, close) ?? false;
  }
  /**
   * Removes all child subscription channels for given topic `id` and if
   * `close` is true (default) also closes them.
   *
   * @param close
   */
  unsubscribeAll(id, close = true) {
    const topic = this.topics[id];
    topic?.unsubscribeAll(close);
  }
  async process() {
    let x;
    while ((x = await this.src.read()) !== void 0) {
      const id = this.fn(x);
      let topic = this.topics[id];
      topic && await topic.write(x);
      x = null;
    }
    for (let t of Object.values(this.topics)) {
      t.close();
    }
    this.topics = {};
  }
}
export {
  PubSub,
  pubsub
};