/**
 * This file is part of Haketilo.
 *
 * Function: Facilitate listening to (internal, self-generated) events.
 *
 * Copyright (C) 2021 Wojtek Kosior
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * As additional permission under GNU GPL version 3 section 7, you
 * may distribute forms of that code without the copy of the GNU
 * GPL normally required by section 4, provided you include this
 * license notice and, in case of non-source distribution, a URL
 * through which recipients can access the Corresponding Source.
 * If you modify file(s) with this exception, you may extend this
 * exception to your version of the file(s), but you are not
 * obligated to do so. If you do not wish to do so, delete this
 * exception statement from your version.
 *
 * As a special exception to the GPL, any HTML file which merely
 * makes function calls to this code, and for that purpose
 * includes it by reference shall be deemed a separate work for
 * copyright law purposes. If you modify this code, you may extend
 * this exception to your version of the code, but you are not
 * obligated to do so. If you do not wish to do so, delete this
 * exception statement from your version.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 *
 * I, Wojtek Kosior, thereby promise not to sue for violation of this file's
 * license. Although I request that you do not make use this code in a
 * proprietary program, I am not going to enforce this in court.
 */

const make = (value=undefined) => ({value, listeners: new Set()});
const subscribe = (observable, cb) => observable.listeners.add(cb);
const unsubscribe = (observable, cb) => observable.listeners.delete(cb);

const silent_set = (observable, value) => observable.value = value;
const broadcast = (observable, ...values) =>
      observable.listeners.forEach(cb => cb(...values));

function set(observable, value)
{
    const old_value = observable.value;
    silent_set(observable, value);
    broadcast(observable, value, old_value);
}

const observables = {make, subscribe, unsubscribe, broadcast, silent_set, set};

/*
 * EXPORTS_START
 * EXPORT observables
 * EXPORTS_END
 */