use crossbeam::channel::{Receiver, Sender};
use std::sync::mpsc;

#[derive(Clone)]
/// A generic job dispatcher struct that allows sending jobs of type `T` and receiving results of type `V` using message passing.
pub struct JobDispatcher<T: Send + 'static, V: Send + 'static> {
    sender: Sender<JobOrder<T, V>>,
}

pub struct JobResult<V>(std::sync::mpsc::Receiver<V>);

impl<V> JobResult<V> {
    /// Wait for the Result of a Job.
    pub fn wait(self) -> V {
        self.0.recv().unwrap()
    }
}

impl<T: Send + 'static, V: Send + 'static> JobDispatcher<T, V> {
    /// Creates a new instance of `JobDispatcher` and returns a tuple that contains it and a receiver end for `JobOrder`s.
    /// # Example:
    /// ```
    /// use jobdispatcher::*;
    /// // Create job dispatcher
    /// let (dispatcher, recv) = JobDispatcher::<i32, i32>::new();
    ///
    /// // Worker Thread
    /// std::thread::spawn(move || {
    ///     for job in recv {
    ///         let result = job.param + 1;
    ///         job.done(result);
    ///     }
    /// });
    ///    
    /// // Usage
    /// let result = dispatcher.send(3);
    /// assert_eq!(result, 4);
    /// ```
    #[must_use]
    pub fn new() -> (Self, Receiver<JobOrder<T, V>>) {
        let (sender, receiver) = crossbeam::channel::bounded(12);

        (Self { sender: sender }, receiver)
    }

    /// Sends a job of type `T` to the job dispatcher and waits for its result of type `V`.
    /// Returns the result of the job once it has been processed.
    /// # Panics
    /// This function panics when the `JobOrder` struct gets out of scope without returning a finished result.
    /// Additionally if the internal `Mutex` is poisoned, this function will panic as well.
    pub fn send(&self, param: T) -> V {
        let (tx, rx) = mpsc::channel();
        let job_order = JobOrder::new(param, move |ret| {
            tx.send(ret).unwrap();
        });
        self.sender.send(job_order).unwrap();
        rx.recv().unwrap()
    }

    pub fn send_async(&self, param: T) -> JobResult<V> {
        let (tx, rx) = mpsc::channel();
        let job_order = JobOrder::new(param, move |ret| {
            tx.send(ret).unwrap();
        });
        self.sender.send(job_order).unwrap();
        JobResult(rx)
    }

    /// Sends a job of type `T` to the job dispatcher and waits for its result of type `V`.
    /// Returns `Some(V)` when the job returns an result, `None` if somehow nothing was returned or the internal `Mutex` is poisoned.
    pub fn try_send(&self, param: T) -> Option<V> {
        let (tx, rx) = mpsc::channel();
        let job_order = JobOrder::new(param, move |ret| {
            tx.send(ret).unwrap();
        });
        self.sender.send(job_order).ok()?;
        rx.recv().ok()
    }
}

/// A struct that represents a job order that encapsulates a job of type `T` and its result of type `V`, along with a callback function that will send the result back to the job origin.
pub struct JobOrder<T, V> {
    /// The job parameter of type `T`.
    pub param: T,
    callback: Box<dyn FnOnce(V) + Send>,
}

impl<T, V> JobOrder<T, V> {
    /// Creates a new `JobOrder` instance with the specified job parameter `param` of type `T` and a callback function that takes the job result of type `V` as an argument.
    #[must_use]
    fn new(param: T, callback: impl FnOnce(V) + Send + 'static) -> Self {
        Self {
            param,
            callback: Box::new(callback),
        }
    }

    /// Send the result of the `JobOrder` back to it's origin
    pub fn done(self, val: V) {
        (self.callback)(val);
    }
}