use std::{
    panic::{self, AssertUnwindSafe},
    thread,
};

pub struct ThreadPool {
    workers: Vec<Worker>,
    sender: Option<crossbeam_channel::Sender<Job>>,
}

type Job = Box<dyn FnOnce() + Send + 'static>;

impl ThreadPool {
    pub fn new(size: usize, max_waiting: usize) -> Self {
        assert!(size > 0);

        let (sender, receiver) = crossbeam_channel::bounded(max_waiting);
        let mut workers = Vec::with_capacity(size);
        for id in 0..size {
            workers.push(Worker::new(id, receiver.clone()));
        }

        ThreadPool {
            workers,
            sender: Some(sender),
        }
    }

    pub fn execute<F>(&self, f: F)
    where
        F: FnOnce() + Send + 'static,
    {
        let job = Box::new(f);
        if let Some(sender) = &self.sender {
            sender.send(job).unwrap();
        }
    }
}

impl Drop for ThreadPool {
    fn drop(&mut self) {
        drop(self.sender.take()); // close channel
        for worker in &mut self.workers {
            if let Some(thread) = worker.thread.take() {
                thread.join().unwrap();
            }
        }
    }
}

#[allow(unused)]
struct Worker {
    id: usize,
    thread: Option<thread::JoinHandle<()>>,
}

impl Worker {
    fn new(id: usize, receiver: crossbeam_channel::Receiver<Job>) -> Self {
        let thread = thread::spawn(move || {
            while let Ok(job) = receiver.recv() {
                let result = panic::catch_unwind(AssertUnwindSafe(job));
                if let Err(e) = result {
                    eprintln!("Worker {id} saw a panic: {e:?}");
                }
            }
        });

        Worker {
            id,
            thread: Some(thread),
        }
    }
}