//!
//! # webserver
//! 
//! One simple webserver. Learn from https://www.youtube.com/watch?v=TOyiliDaK30&list=PL3azK8C0kje1DUJbaOqce19j3R_-tIc4_&index=110.

use std::thread;
use std::sync::mpsc;
use std::sync::Arc;
use std::sync::Mutex;

enum Message {
    NewJob(Job),
    Terminate,
}

pub struct ThreadPool
{
    workers: Vec<Worker>,
    sender:mpsc::Sender<Message>,
}


// struct Job;

trait FnBox {
    fn call_box(self:Box<Self>);
}

impl<F:FnOnce()> FnBox for F{
    fn call_box(self:Box<F>){
        (*self)()
    }
}

type Job = Box<dyn FnBox+ Send+ 'static>;

impl ThreadPool {
    /// Create a new ThreadPool
    /// 
    /// The size is the number of threads in the pool.
    /// 
    /// 
    pub fn new(size:usize)->ThreadPool{
        assert!(size>0);
        let mut workers = Vec::with_capacity(size);

        let (sender,receiver) = mpsc::channel();
        let receiver = Arc::new(Mutex::new(receiver));
        
        for id in 0..size{
            workers.push(Worker::new(id,Arc::clone(&receiver)));
        }
        ThreadPool { workers,sender }
    }

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

    }
}

struct Worker {
    id: usize,
    thread: Option<thread::JoinHandle<()>>,
}

impl Worker {
    fn new(id: usize,receiver:Arc<Mutex<mpsc::Receiver<Message>>>)->Worker{

        let thread = thread::spawn(move|| loop{
            let message = receiver.lock().unwrap().recv().unwrap();
            match message {
                Message::NewJob(job) => {
                    job.call_box();
                },
                Message::Terminate => {
                    println!("worker {} was told to terminate.",id);
                    break;
                }
            }
            
        });

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

impl Drop for ThreadPool {
    fn drop(&mut self) {
        for _ in &mut self.workers {
            self.sender.send(Message::Terminate).unwrap();
        }

        for worker in &mut self.workers {

            if let Some(thread) = worker.thread.take(){
                thread.join().unwrap();
            };
        }
    }
}