import { SERVER, SERVER_OPTIONS } from '../server.ts';

const BASE_PORT: number = 50_000;
const MAX_PORT_OFFSET: number = 10_000;
let current_port_offset = 0;
function get_next_free_port(): number {
	let free_port: number | undefined = undefined;
	let attempts = 0;
	do {
		const port_to_try: number = BASE_PORT + (current_port_offset++ % MAX_PORT_OFFSET);

		try {
			Deno.listen({ port: port_to_try }).close();
			free_port = port_to_try;
		} catch (error) {
			if (!(error instanceof Deno.errors.AddrInUse)) {
				throw error;
			}
		}

		++attempts;

		if (attempts % MAX_PORT_OFFSET === 0) {
			console.warn(`Tried all ports at least once while trying to locate a free one, something wrong?`);
		}
	} while (!free_port);

	return free_port;
}

/**
 * Interface defining the configuration for an ephemeral server
 * @property {string} hostname - hostname bound to, default: 'localhost'
 * @property {number} port - port bound to, default: next free port
 * @property {SERVER} server - server instance
 */
export interface EPHEMERAL_SERVER {
	hostname: string;
	port: number;
	server: SERVER;
}

/**
 * Gets an ephemeral Serverus SERVER on an unused port.
 *
 * @param options Optional SERVER_OPTIONS
 * @returns A LISTEN_SERVER_SETUP object with information and a reference to the server
 */
export async function get_ephemeral_listen_server(options?: SERVER_OPTIONS): Promise<EPHEMERAL_SERVER> {
	const server_options = {
		...{
			hostname: 'localhost',
			port: get_next_free_port()
		},
		...(options ?? {})
	};

	const server = new SERVER(server_options);

	const ephemeral_server: EPHEMERAL_SERVER = {
		hostname: server_options.hostname,
		port: server_options.port,
		server: await server.start()
	};

	return ephemeral_server;
}