dpaw-brocket-channel/src/channel.js

Fundamental communication component

/**
 * @fileOverview
 * @name channel.js
 * @author Gavin Coombes
 * @license BSD-3-License
 *
 * A channel object participates in the stream interface.
 * A channel can be a
 *  - source channel
 *  - sink channel
 *  - transit channel.
 *
 * A source channel must have a subscribe method to pull messages out.
 * A sink channel must have a dispatch method to push messages in.
 * A transit channel must have both.
 */


let u = require('dpaw-brocket-utility');
let events = require('events');

// Local Aliases
var log = u.log;

var ChannelModule = (function(){
  let obj = Object.create(new events.EventEmitter());
  obj.$type = "ChannelModule";
  return obj;
})();

var ChannelObject = Object.create(ChannelModule);

ChannelObject.$init = function init(opts){
  let self = this;
  self.opts = opts;
  self.type = 'ChannelObject';
  self.subscriptions = Object.create({});
};

ChannelObject.$subscribe = function subscribe(...args) {
  /** Register a callback for each received message.
   *
   * Register a callback for every message.
   * var f = msg => log('Received msg ', msg);
   * relay.subscribe(f)
   *
   * Register a callback for messages with an appTag of 'bounds'
   * var g = msg => log('Received bounds message');
   * relay.subscribe('bounds', g)
   */
  let self = this;
  let [tag, cb] = args;
  if (!cb) [tag, cb] = ['global', tag];
  self.subscriptions = addSubscription(self.subscriptions, tag, cb);
};


module.exports = ChannelObject;

function create(parent, opts) {
  let child = Object.create(parent);
  child.init(opts);
  return child;
}

function addSubscription(subs, key, val) {
  if (!u.has(subs, key)) subs[key] = [];
  subs[key] = [...subs[key], val];
  return subs;
}