interactor/interactor.js

import { Stream } from "stream";

export class Interactor {
  #actions = new Stream();
  #reactions = new Stream();
  #latestReaction;
  #latestReactions = {};

  constructor(initialReaction = new Reaction()) {
    this.#actions.listen((action) =>
      this[`handle${action.constructor.name}`](action)
    );
    this._react(initialReaction);
  }

  act(action) {
    if (!(action instanceof Action)) throw "invalid action";
    this.#actions.add(action);
  }

  observe(reactionHandler, provideLatestReaction = true) {
    if (provideLatestReaction) reactionHandler(this.#latestReaction);
    let listener = (reaction) => {
      if (!(reaction instanceof Reaction)) throw "invalid reaction";
      reactionHandler(reaction);
    };
    this.#reactions.listen(listener);
    return listener;
  }

  ignore(listener) {
    this.#reactions.ignore(listener);
  }

  _react(reaction) {
    if (!(reaction instanceof Reaction)) throw "invalid reaction";
    let latest = this.#latestReactions[reaction.constructor.name];
    if (!reaction.equals(latest)) {
      this.#latestReaction = reaction;
      this.#latestReactions[reaction.constructor.name] = reaction;
      this.#reactions.add(reaction);
    }
  }
}

export class Action {}

export class Reaction {
  equals(reaction) {
    return false;
  }
}