/**
 * Forked from https://github.com/digitalloggers/race-as-promised/tree/master
 *
 * Authored by Brian Kim:
 * https://github.com/nodejs/node/issues/17469#issuecomment-685216777
 *
 * Adapted to module structure.
 *
 * This is free and unencumbered software released into the public domain.
 *
 * Anyone is free to copy, modify, publish, use, compile, sell, or
 * distribute this software, either in source code form or as a compiled
 * binary, for any purpose, commercial or non-commercial, and by any
 * means.
 *
 * In jurisdictions that recognize copyright laws, the author or authors
 * of this software dedicate any and all copyright interest in the
 * software to the public domain. We make this dedication for the benefit
 * of the public at large and to the detriment of our heirs and
 * successors. We intend this dedication to be an overt act of
 * relinquishment in perpetuity of all present and future rights to this
 * software under copyright law.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 *
 * For more information, please refer to <http://unlicense.org/>
 */

type Deferred = Readonly<{
    reject: (reason?: unknown) => void;
    resolve: (value: unknown) => void;
}>;

function isObject(value: unknown): value is object {
    return value !== null && (typeof value === 'object' || typeof value === 'function');
}

function addRaceContender(contender: object) {
    const deferreds = new Set<Deferred>();
    const record = { deferreds, settled: false };

    // This call to `then` happens once for the lifetime of the value.
    Promise.resolve(contender).then(
        value => {
            for (const { resolve } of deferreds) {
                resolve(value);
            }

            deferreds.clear();
            record.settled = true;
        },
        err => {
            for (const { reject } of deferreds) {
                reject(err);
            }

            deferreds.clear();
            record.settled = true;
        },
    );
    return record;
}

// Keys are the values passed to race, values are a record of data containing a
// set of deferreds and whether the value has settled.
const wm = new WeakMap<object, { deferreds: Set<Deferred>; settled: boolean }>();
/**
 * An implementation of [`Promise.race`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/race)
 * that causes all of the losing promises to settle. This allows them to be released and garbage
 * collected, preventing memory leaks.
 *
 * Read more here: https://github.com/nodejs/node/issues/17469
 */
export async function safeRace<T extends readonly unknown[] | []>(contenders: T): Promise<Awaited<T[number]>> {
    let deferred: Deferred;
    const result = new Promise((resolve, reject) => {
        deferred = { reject, resolve };
        for (const contender of contenders) {
            if (!isObject(contender)) {
                // If the contender is a primitive, attempting to use it as a key in the
                // weakmap would throw an error. Luckily, it is safe to call
                // `Promise.resolve(contender).then` on a primitive value multiple times
                // because the promise fulfills immediately.
                Promise.resolve(contender).then(resolve, reject);
                continue;
            }

            let record = wm.get(contender);
            if (record === undefined) {
                record = addRaceContender(contender);
                record.deferreds.add(deferred);
                wm.set(contender, record);
            } else if (record.settled) {
                // If the value has settled, it is safe to call
                // `Promise.resolve(contender).then` on it.
                Promise.resolve(contender).then(resolve, reject);
            } else {
                record.deferreds.add(deferred);
            }
        }
    });

    // The finally callback executes when any value settles, preventing any of
    // the unresolved values from retaining a reference to the resolved value.
    return await (result.finally(() => {
        for (const contender of contenders) {
            if (isObject(contender)) {
                const record = wm.get(contender)!;
                record.deferreds.delete(deferred);
            }
        }
    }) as Promise<Awaited<T[number]>>);
}