import * as http from 'http';

export const getPort = (startPort: number): Promise<number> => {
    const tryGetPort = (cb: (num: number) => void) => {
        var port = startPort;
        startPort += 1;

        var server = http.createServer(() => null);

        server.on('error', (err) => {
            tryGetPort(cb);
        });
        server.listen(port, '0.0.0.0' as any, ((err) => {
            // Found one!
            server.once('close', () => {
                cb(port);
            });
            server.close();
        }) as any);
    }

    let resolve: (num: number) => void;
    const prom = new Promise<number>(res => resolve = res);
    tryGetPort(resolve);
    return prom;
};