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 ActionBundle {
  add(action) {
    if (!(action.prototype instanceof Action)) {
      throw "Only classes extended by `Action` can be added to a `ActionBundle`";
    }
    let actionName = action.name;
    this[`#${actionName}`] = action;
    Object.defineProperty(this, actionName, {
      get: () => this[`#${actionName}`],
    });
  }
}

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

export class ReactionBundle {
  add(reaction) {
    if (!(reaction.prototype instanceof Reaction)) {
      throw "Only classes extended by `Reaction` can be added to a `ReactionBundle`";
    }
    let reactionName = reaction.name;
    this[`#${reactionName}`] = reaction;
    Object.defineProperty(this, reactionName, {
      get: () => this[`#${reactionName}`],
    });
  }
}