//! Creates a worker thread and exposes a sender to communidate with
use async_trait::async_trait;
use std::{ops::Deref, sync::Arc};
use tokio::{
    sync::mpsc::{channel, Sender},
    task::JoinHandle,
};

/// The maximum size for buffering messages
const WORKER_BUFFER_SIZE: usize = 1_000;

/// Worker trait
///
/// The worker trait has the definition of the code the worker has to perform in a different thread
#[async_trait]
pub trait Worker: Send + Sync {
    type Payload: Send + Sync + Clone;

    /// Method to be executed with a given task
    async fn handle(&self, payload: Self::Payload);

    /// Whether or not to process the request
    fn process_request(&self) -> bool {
        true
    }
}

/// Worker manager
///
/// The worker manager manages the instances of the Worker trait, which is executed asynchronously
/// in a separate thread from the send() context.
///
/// The logic of having one or more instances of the Worker trait is abstracted in this structure.
#[derive(Debug)]
pub struct WorkerManager<W: Worker> {
    sender: Sender<W::Payload>,
    worker_thread: JoinHandle<()>,
    worker: Arc<W>,
}

impl<W: Worker> Drop for WorkerManager<W> {
    fn drop(&mut self) {
        self.worker_thread.abort();
    }
}

impl<W: Worker> Deref for WorkerManager<W> {
    type Target = Arc<W>;

    fn deref(&self) -> &Self::Target {
        &self.worker
    }
}

impl<W: Worker + 'static> WorkerManager<W> {
    /// Creates a new WorkerManager given a struct that implements the Worker trait
    pub fn new(worker: W) -> Self {
        let worker = Arc::new(worker);
        let (worker_thread, sender) = WorkerManager::start_background_worker(worker.clone());
        Self {
            sender,
            worker_thread,
            worker,
        }
    }

    fn start_background_worker(worker: Arc<W>) -> (JoinHandle<()>, Sender<W::Payload>) {
        let (sender, mut receiver) = channel(WORKER_BUFFER_SIZE);
        (
            tokio::spawn(async move {
                while let Some(message) = receiver.recv().await {
                    worker.handle(message).await;
                }
            }),
            sender,
        )
    }

    /// Sends a message to be processed in another thread
    pub fn process(&self, message: W::Payload) {
        if self.worker.process_request() {
            let _ = self.sender.try_send(message);
        }
    }
}