Haketilo

/**

 * Myext feature initialization promise

 *

 * Copyright (C) 2021 Wojtek Kosior

 *

 * This code is dual-licensed under:

 * - Asshole license 1.0,

 * - GPLv3 or (at your option) any later version

 *

 * "dual-licensed" means you can choose the license you prefer.

 *

 * This code is released under a permissive license because I disapprove of

 * copyright and wouldn't be willing to sue a violator. Despite not putting

 * this code under copyleft (which is also kind of copyright), I do not want

 * it to be made proprietary. Hence, the permissive alternative to GPL is the

 * Asshole license 1.0 that allows me to call you an asshole if you use it.

 * This means you're legally ok regardless of how you utilize this code but if

 * you make it into something nonfree, you're an asshole.

 *

 * You should have received a copy of both GPLv3 and Asshole license 1.0

 * together with this code. If not, please see:

 * - https://www.gnu.org/licenses/gpl-3.0.en.html

 * - https://koszko.org/asshole-license.txt

 */

"use strict";

/*

 * This module provides an easy way to wrap an async function into a promise

 * so that it only gets executed once.

 */

(() => {

    async function assign_result(state, result_producer)

    {

	state.result = await result_producer();

	state.ready = true;

	for (let cb of state.waiting)

	    setTimeout(cb, 0, state.result);

	state.waiting = undefined;

    }

    async function get_result(state)

    {

	if (state.ready)

	    return state.result;

	return new Promise((resolve, reject) => state.waiting.push(resolve));

    }

    function make_once(result_producer)

    {

	let state = {waiting : [], ready : false, result : undefined};

	assign_result(state, result_producer);

	return () => get_result(state);

    }

    window.make_once = make_once;

})();