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#![doc(html_logo_url = "https://avatars3.githubusercontent.com/u/15439811?v=3&s=200",
       html_favicon_url = "https://iorust.github.io/favicon.ico",
       html_root_url = "https://iorust.github.io",
       html_playground_url = "https://play.rust-lang.org",
       issue_tracker_base_url = "https://github.com/iorust/thunks/issues")]

//! Asynchronous composer for Rust.

// use std::thread;
use std::sync::mpsc::{Receiver, sync_channel};
use std::boxed::{Box};

pub struct Thunk<T, E>(Box<Fn(Box<Fn(Result<T, E>) + Send + 'static>) + Send + 'static>);

impl<T, E> Thunk<T, E> where T: Send + 'static, E: Send + 'static {
    pub fn new<F>(task: F) -> Thunk<T, E>
    where F: Fn(Box<Fn(Result<T, E>) + Send + 'static>) + Send + 'static {
        Thunk(Box::new(task))
    }

    pub fn seq(thunk_vec: Vec<Thunk<T, E>>) -> Thunk<Vec<T>, E> {
        let thunk_vec = Box::new(thunk_vec);
        Thunk::new(move |cb| {
            let mut res: Vec<T> = Vec::new();
            for thunk in thunk_vec.iter() {
                match thunk.await() {
                    Ok(val) => res.push(val),
                    Err(err) => {
                        cb(Err(err));
                        return;
                    }
                }
            }
            cb(Ok(res));
        })
    }

    pub fn all(thunk_vec: Vec<Thunk<T, E>>) -> Thunk<Vec<T>, E> {
        let thunk_vec = Box::new(thunk_vec);
        Thunk::new(move |cb| {
            let mut res: Vec<T> = Vec::new();
            let rx_vec: Vec<Receiver<Result<T, E>>> = thunk_vec.iter()
                .map(|t| t.call_thunk()).collect();

            for rx in rx_vec.iter() {
                match rx.recv().unwrap() {
                    Ok(val) => res.push(val),
                    Err(err) => {
                        cb(Err(err));
                        return;
                    }
                }
            }
            cb(Ok(res));
        })
    }

    pub fn await(&self) -> Result<T, E> {
        self.call_thunk().recv().unwrap()
    }

    fn call_thunk(&self) -> Receiver<Result<T, E>> {
        let (tx, rx) = sync_channel::<Result<T, E>>(1);
        (self.0)(Box::new(move |res| {
            tx.try_send(res).unwrap();
        }));
        rx
    }
}

#[cfg(test)]
mod tests {
    use std::thread;
    use std::time::Duration;
    use super::*;

    #[test]
    fn thunk() {
        let thunk: Thunk<i32, &str> = Thunk::new(|cb| {
            thread::spawn(move || {
                thread::sleep(Duration::new(3, 0));
                cb(Ok(1));
            });
        });
        let res = thunk.await().unwrap();
        // println!("{:?}", res);
        assert_eq!(res, 1);
    }

    #[test]
    fn thunk_seq() {
        let thunk_vec: Vec<Thunk<i32, &str>> = vec![
            Thunk::new(|cb| {
                thread::spawn(move || {
                    thread::sleep(Duration::new(1, 0));
                    cb(Ok(1));
                });
            }),
            Thunk::new(|cb| {
                thread::spawn(move || {
                    thread::sleep(Duration::new(1, 0));
                    cb(Ok(2));
                });
            }),
            Thunk::new(|cb| {
                thread::spawn(move || {
                    thread::sleep(Duration::new(1, 0));
                    cb(Ok(3));
                });
            })
        ];
        let res = Thunk::seq(thunk_vec).await().unwrap();
        assert_eq!(res, vec![1, 2, 3]);
    }

    #[test]
    fn thunk_all() {
        let thunk_vec: Vec<Thunk<i32, &str>> = vec![
            Thunk::new(|cb| {
                thread::spawn(move || {
                    thread::sleep(Duration::new(1, 0));
                    cb(Ok(1));
                });
            }),
            Thunk::new(|cb| {
                thread::spawn(move || {
                    thread::sleep(Duration::new(1, 0));
                    cb(Ok(2));
                });
            }),
            Thunk::new(|cb| {
                thread::spawn(move || {
                    thread::sleep(Duration::new(1, 0));
                    cb(Ok(3));
                });
            })
        ];
        let res = Thunk::all(thunk_vec).await().unwrap();
        assert_eq!(res, vec![1, 2, 3]);
    }
}