// Kubernetes uses the following command to spawn Docker containers:
// docker run --cpuset-cpus="0,1" to assign only 2 CPUs.
// However, Node.js returns the core count of the host system (up to 96!)

import {execSync} from 'node:child_process';
import os from 'node:os';

let nprocCount: number | null | undefined;

// We also get it from nproc and use the minimum of the two.
export const getConcurrencyFromNProc = (): number | null => {
	if (nprocCount !== undefined) {
		return nprocCount;
	}

	try {
		const count = parseInt(
			execSync('nproc', {stdio: 'pipe'}).toString().trim(),
			10,
		);
		nprocCount = count;
		return count;
	} catch {
		return null;
	}
};

const getNodeCpuCount = (): number => {
	// os.availableParallelism() is faster and respects cgroup CPU limits in containers.
	// Available since Node 18.14 / 19.4.
	if (typeof os.availableParallelism === 'function') {
		return os.availableParallelism();
	}

	return os.cpus().length;
};

export const getCpuCount = () => {
	const node = getNodeCpuCount();
	const nproc = getConcurrencyFromNProc();
	if (nproc === null) {
		return node;
	}

	return Math.min(nproc, node);
};