/**
 * 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;
})();