extern crate futures;
extern crate tokio;

use futures::future::ok;
use futures::{Future, Stream};
use tokio::prelude::future::lazy;
use tokio::runtime::current_thread::Runtime;

fn get_times2_future(number: u32) -> impl Future<Item = u32, Error = ()> {
    ok(number * 2)
}

fn get_times_future(number: u32, times: u32) -> impl Future<Item = u32, Error = ()> {
    ok(number * times)
}

fn main() {
    let numbers = vec![1, 2, 3];
    let mut runtime = Runtime::new().unwrap();
    let calculations = runtime.block_on(lazy(|| {
        let calc_futures = numbers.iter().map(|number| get_times2_future(*number));
        let first_level = futures::stream::futures_unordered(calc_futures);
        let second_level = first_level.and_then(|num| {
            Ok(futures::stream::futures_unordered(
                vec![10, 100, 1000].iter().map(|times| get_times_future(num, *times))
            ))
        });
        second_level.flatten().for_each(|resp| {
            println!("{}", resp);
            Ok(())
        })
    }));
    if let Err(_) = calculations {
        println!("error")
    }
}