//! # `threadpool-simple` beta
//! Create threads and give them jobs very simply!
//! 
//!
//! # Example
//! 
//! ```
//! struct ThreadPool {
//!     worker: Vec<Worker>,
//!     sender:  mpsc::Sender<Job>,
//! ```
//! Using channels for sending/receiving jobs between threads
//! 
//! 
use std::thread;
use std::sync::{Mutex, Arc, Condvar, MutexGuard, mpsc};
use std::time::Duration;

/// Alias for the type of a job, representing a closure or function that takes no arguments and does not return a value.
type Job = Box<dyn FnOnce() + Send + 'static>;

/// Struct representing a thread pool.
struct ThreadPool {
    workers: Vec<Worker>,
    sender: mpsc::Sender<Job>,
}

impl ThreadPool {
    /// Creates a new thread pool with the specified size.
    ///
    /// # Arguments
    ///
    /// * `size` - The number of threads in the thread pool.
    ///
    /// # Panics
    ///
    /// Panics if the `size` is 0.
    fn new(size: usize) -> Self {
        assert!(size > 0);

        let (sender, receiver) = mpsc::channel();
        let receiver = Arc::new(Mutex::new(receiver));
        let mut workers = Vec::with_capacity(size);

        for id in 0..size {
            workers.push(Worker::new(id, Arc::clone(&receiver)));
        }

        ThreadPool { workers, sender }
    }

    /// Executes a job in the thread pool.
    ///
    /// # Arguments
    ///
    /// * `f` - The closure or function representing the job to be executed.
    ///
    /// # Example
    ///
    /// ```
    /// let pool = ThreadPool::new(4);
    ///
    /// pool.execute(move || {
    ///     println!("Working on a job");
    /// });
    /// ```
    fn execute<F>(&self, f: F)
    where
        F: FnOnce() + Send + 'static,
    {
        let job = Box::new(f);
        self.sender.send(job).expect("Error while sending job in pool");
    }
}

/// Struct representing a worker in the thread pool.
struct Worker {
    id: usize,
    thread: thread::JoinHandle<()>,
}

impl Worker {
    /// Creates a new worker associated with the given ID and the receiver for job messages.
    ///
    ///! # Arguments
    ///!
    ///! * `id` - The ID of the worker.
    ///! * `receiver` - The receiver for job messages.
    fn new(id: usize, receiver: Arc<Mutex<mpsc::Receiver<Job>>>) -> Worker {
        let thread = thread::spawn(move || loop {
            let job = receiver.lock().unwrap().recv().unwrap();
            println!("[THREAD{}] IS WORKING", id);
            job();
        });

        Worker { id, thread }
    }
}

/*
```
fn main() {
    let pool = ThreadPool::new(100);
    for i in 0..10 {
        pool.execute(move || {
            println!("Working on {i}");
        });
    }
    thread::sleep(Duration::from_millis(1000));
}
```*/