import http from 'http';
import * as client from 'prom-client';
import config from 'lib/Config';
import { Log } from 'lib/Log';

const log = Log.child({
	method: 'Metrics',
});

/** Register default node metrics to collect */
// eslint-disable-next-line @typescript-eslint/no-unsafe-call,@typescript-eslint/no-unsafe-member-access
client.collectDefaultMetrics({});

/** Spawn a server to handle metrics requests */
const server = http.createServer((req, res) => {
	log.trace('Fetch metrics');

	// eslint-disable-next-line @typescript-eslint/no-unsafe-call,@typescript-eslint/no-unsafe-member-access
	client.register
		.metrics()
		.then((metrics: string) => {
			res
				.writeHead(200, {
					'Content-Length': Buffer.byteLength(metrics),
					'Content-Type': 'text/plain',
				})
				.end(metrics);
		})
		.catch((err: Error) => {
			log.error('Failed to resolve metrics', err);
			res
				.writeHead(500, {
					'Content-Type': 'text/plain',
				})
				.end();
		});
});

// Only listen to internal requests
if (config.metrics.enabled) {
	const { host, port } = config.metrics;
	const hostname = `${host}:${port}`;
	log.info('Registering metrics server %s (env: %s) @ %s', config.app.name, config.env, hostname);

	server.listen(+port, host, () => {
		log.info('Metrics for %s (env: %s) started @ %s', config.app.name, config.env, hostname);
	});
} else log.info('Metrics disabled for this service');

export default client;