use futures::prelude::*;
use tokio::prelude::*;

use std::{io, path::PathBuf};

type BoxedFutureFileSize = Box<dyn Future<Item = u64, Error = io::Error>>;

fn recursive_size(path: PathBuf) -> impl Future<Item = u64, Error = io::Error> {
    tokio::fs::symlink_metadata(path.clone())
        .and_then::<_, BoxedFutureFileSize>(|metadata| {
            if metadata.is_file() {
                Box::new(future::ok(metadata.len()))
            } else {
                let sizes = tokio::fs::read_dir(path)
                    .flatten_stream()
                    .and_then(|entry| recursive_size(entry.path()));
                Box::new(sizes.fold(0, |acc, x| future::ok::<_, io::Error>(acc + x)))
            }
        })
}