// requestIdleCallback sortof-polyfill
if (!self.requestIdleCallback) {
	const IDLE_TIMEOUT = 10;
	self.requestIdleCallback = cb => {
		let start = Date.now();
		return setTimeout(
			() =>
				cb({
					timeRemaining: () => Math.max(0, IDLE_TIMEOUT - (Date.now() - start))
				}),
			1
		);
	};
	self.requestIdleCallback = clearTimeout;
}

export function backgroundTask(fn, timeout = undefined) {
	let id = null;
	const params = [];

	async function runTask({ didTimeout }) {
		if (didTimeout) {
			id = requestIdleCallback(runTask);
			return;
		}
		const start = Date.now();
		const p = params.shift();
		await fn(...p);
		if (params.length) {
			id = requestIdleCallback(runTask, { timeout });
		} else {
			id = null;
		}
	}

	const wrapper = (...args) => {
		params.push(args);
		if (id !== null) {
			return false;
		}
		id = requestIdleCallback(runTask, { timeout });
		return true;
	};

	return wrapper;
}