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/*
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 *  This file is part of CoCalc: Copyright © 2020 Sagemath, Inc.
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 *  License: MS-RSL – see LICENSE.md for details
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 */
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/*
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Wait until some function until of obj is truthy
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(not truthy includes "throw an exception").
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Waits until "until(obj)" evaluates to something truthy
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in *seconds* -- set to 0 to disable (sort of DANGEROUS, obviously.)
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Returns until(obj) on success and raises Error('timeout') or
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Error('closed') on failure (closed if obj emits
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'closed' event.
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obj is an event emitter, and obj should emit change_event
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whenever it changes.
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obj should emit 'close' if it prematurely ends.
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The until function may be async.
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The timeout can be 0 to disable timeout.
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*/
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import { callback } from "awaiting";
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import { EventEmitter } from "events";
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interface WaitObject extends EventEmitter {
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  get_state: Function;
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}
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export async function wait({
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  obj,
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  until,
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  timeout,
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  change_event,
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}: {
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  obj: WaitObject;
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  until: Function;
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  timeout: number;
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  change_event: string;
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}): Promise<any> {
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  function wait(cb): void {
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    let fail_timer: any = undefined;
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    function done(err, ret?): void {
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      obj.removeListener(change_event, f);
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      obj.removeListener("close", f);
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      if (fail_timer !== undefined) {
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        clearTimeout(fail_timer);
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        fail_timer = undefined;
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      }
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      if (cb === undefined) {
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        return;
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      }
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      cb(err, ret);
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      cb = undefined;
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    }
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    async function f() {
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      if (obj.get_state() === "closed") {
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        done(`closed - wait-until - ${change_event}`);
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        return;
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      }
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      let x;
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      try {
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        x = await until(obj);
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      } catch (err) {
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        done(err);
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        return;
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      }
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      if (x) {
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        done(undefined, x);
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      }
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    }
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    obj.on(change_event, f);
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    obj.on("close", f);
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    if (timeout) {
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      const fail = () => {
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        done("timeout");
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      };
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      fail_timer = setTimeout(fail, 1000 * timeout);
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    }
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    // It might already be true (even before event fires):
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    f();
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  }
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  return await callback(wait);
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}
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