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/**
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* This file is part of Haketilo.
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*
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* Function: Wrap APIs that depend on some asynchronous initialization into
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* promises.
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*
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* Copyright (C) 2021 Wojtek Kosior
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* As additional permission under GNU GPL version 3 section 7, you
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* may distribute forms of that code without the copy of the GNU
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* GPL normally required by section 4, provided you include this
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* license notice and, in case of non-source distribution, a URL
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* through which recipients can access the Corresponding Source.
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* If you modify file(s) with this exception, you may extend this
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* exception to your version of the file(s), but you are not
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* obligated to do so. If you do not wish to do so, delete this
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* exception statement from your version.
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*
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* As a special exception to the GPL, any HTML file which merely
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* makes function calls to this code, and for that purpose
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* includes it by reference shall be deemed a separate work for
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* copyright law purposes. If you modify this code, you may extend
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* this exception to your version of the code, but you are not
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* obligated to do so. If you do not wish to do so, delete this
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* exception statement from your version.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <https://www.gnu.org/licenses/>.
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*
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* I, Wojtek Kosior, thereby promise not to sue for violation of this file's
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* license. Although I request that you do not make use this code in a
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* proprietary program, I am not going to enforce this in court.
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*/
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/*
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* This module provides an easy way to wrap an async function into a promise
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* so that it only gets executed once.
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*/
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async function assign_result(state, result_producer)
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{
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state.result = await result_producer();
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state.ready = true;
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for (let cb of state.waiting)
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setTimeout(cb, 0, state.result);
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state.waiting = undefined;
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}
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async function get_result(state)
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{
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if (state.ready)
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return state.result;
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return new Promise((resolve, reject) => state.waiting.push(resolve));
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}
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function make_once(result_producer)
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{
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let state = {waiting : [], ready : false, result : undefined};
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assign_result(state, result_producer);
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return () => get_result(state);
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}
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/*
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* EXPORTS_START
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* EXPORT make_once
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* EXPORTS_END
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*/
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