use crate::parallel::{num_threads, Reducer};
use crossbeam_utils::thread;

pub fn join<O1: Send, O2: Send>(left: impl FnOnce() -> O1 + Send, right: impl FnOnce() -> O2 + Send) -> (O1, O2) {
    thread::scope(|s| {
        let left = s.spawn(|_| left());
        let right = s.spawn(|_| right());
        (left.join().unwrap(), right.join().unwrap())
    })
    .unwrap()
}

pub fn in_parallel<I, S, O, R>(
    input: impl Iterator<Item = I> + Send,
    thread_limit: Option<usize>,
    new_thread_state: impl Fn(usize) -> S + Send + Sync,
    consume: impl Fn(I, &mut S) -> O + Send + Sync,
    mut reducer: R,
) -> Result<<R as Reducer>::Output, <R as Reducer>::Error>
where
    R: Reducer<Input = O>,
    I: Send,
    O: Send,
{
    let num_threads = num_threads(thread_limit);
    let new_thread_state = &new_thread_state;
    let consume = &consume;
    thread::scope(move |s| {
        let receive_result = {
            let (send_input, receive_input) = crossbeam_channel::bounded::<I>(num_threads);
            let (send_result, receive_result) = std::sync::mpsc::sync_channel::<O>(num_threads);
            for thread_id in 0..num_threads {
                s.spawn({
                    let send_result = send_result.clone();
                    let receive_input = receive_input.clone();
                    move |_| {
                        let mut state = new_thread_state(thread_id);
                        for item in receive_input {
                            if send_result.send(consume(item, &mut state)).is_err() {
                                break;
                            }
                        }
                    }
                });
            }
            s.spawn(move |_| {
                for item in input {
                    if send_input.send(item).is_err() {
                        break;
                    }
                }
            });
            receive_result
        };

        for item in receive_result {
            reducer.feed(item)?;
        }
        reducer.finalize()
    })
    .unwrap()
}