/**
 * Cuts down potentially long or infinite loops to prevent blocking the event loop.
 *
 * Example:
 *     snip(10, 500, function*() {
 *         for (let i = 0; i < 1e100; i++, yield) {
 *             console.log(i);
 *         }
 *         console.log('Done!');
 *     });
 *
 *     let check = false;
 *     snip(1, 1000, function*() {
 *         while (!check) {
 *             console.log('check = false');
 *             yield;
 *         }
 *         console.log('Done!');
 *     });
 *     setTimeout(() => check = true, 10000);
 *
 * @param  {number} interval       The number of times that `yield` will be called until it times out.
 * @param  {number} cooldown       The amount of time in milliseconds between each interval.
 * @param  {function*(): any} gen  The generator function. Each `yield` gives the current count within the interval (from 0 to interval).
 * @return {Promise<any>}          Gives the return value of gen.
 */
function snip(interval, cooldown, gen) {
    return new Promise(function(resolve, reject) {
        let g = gen(), v, i;
        setTimeout(function loop() {
            try {
                for (i = 0; i < interval; i++) {
                    v = g.next(i);
                    if (v.done) {
                        this.ended = true;
                        resolve(v.value);
                        return;
                    }
                }
                setTimeout(loop, cooldown);
            } catch (e) {
                reject(e);
            }
        }, 0);
    });
}