codemp/src/cursor/controller.rs

//! ### controller
//!
//! a controller implementation for cursor actions
use std::sync::Arc;

use tokio::sync::{
	broadcast::{
		self,
		error::{RecvError, TryRecvError},
	},
	mpsc, watch, Mutex,
};
use tonic::async_trait;

use crate::api::{Controller, Cursor};
use codemp_proto::cursor::{CursorEvent, CursorPosition};
/// the cursor controller implementation
///
/// this contains
/// * the unique identifier of current user
/// * a sink to send movements into
/// * a mutex over a stream of inbound cursor events
/// * a channel to stop the associated worker
///
/// for each controller a worker exists , managing outgoing and inbound event queues
///
/// upon dropping this handle will stop the associated worker
#[derive(Debug, Clone)]
#[cfg_attr(feature = "python", pyo3::pyclass)]
#[cfg_attr(feature = "js", napi_derive::napi)]
pub struct CursorController(pub(crate) Arc<CursorControllerInner>);

#[derive(Debug)]
pub(crate) struct CursorControllerInner {
	op: mpsc::UnboundedSender<CursorPosition>,
	last_op: Mutex<watch::Receiver<CursorEvent>>,
	stream: Mutex<broadcast::Receiver<CursorEvent>>,
	stop: mpsc::UnboundedSender<()>,
}

impl CursorControllerInner {
	pub(crate) fn new(
		op: mpsc::UnboundedSender<CursorPosition>,
		last_op: Mutex<watch::Receiver<CursorEvent>>,
		stream: Mutex<broadcast::Receiver<CursorEvent>>,
		stop: mpsc::UnboundedSender<()>,
	) -> Self {
		Self {
			op,
			last_op,
			stream,
			stop,
		}
	}
}

#[async_trait]
impl Controller<Cursor> for CursorController {
	/// enqueue a cursor event to be broadcast to current workspace
	/// will automatically invert cursor start/end if they are inverted
	fn send(&self, mut cursor: Cursor) -> crate::Result<()> {
		if cursor.start > cursor.end {
			std::mem::swap(&mut cursor.start, &mut cursor.end);
		}
		Ok(self.0.op.send(cursor.into())?)
	}

	/// try to receive without blocking, but will still block on stream mutex
	fn try_recv(&self) -> crate::Result<Option<Cursor>> {
		let mut stream = self.0.stream.blocking_lock();
		match stream.try_recv() {
			Ok(x) => Ok(Some(x.into())),
			Err(TryRecvError::Empty) => Ok(None),
			Err(TryRecvError::Closed) => Err(crate::Error::Channel { send: false }),
			Err(TryRecvError::Lagged(n)) => {
				tracing::warn!("cursor channel lagged, skipping {} events", n);
				Ok(stream.try_recv().map(|x| x.into()).ok())
			}
		}
	}

	// TODO is this cancelable? so it can be used in tokio::select!
	// TODO is the result type overkill? should be an option?
	/// get next cursor event from current workspace, or block until one is available
	async fn recv(&self) -> crate::Result<Cursor> {
		let mut stream = self.0.stream.lock().await;
		match stream.recv().await {
			Ok(x) => Ok(x.into()),
			Err(RecvError::Closed) => Err(crate::Error::Channel { send: false }),
			Err(RecvError::Lagged(n)) => {
				tracing::error!("cursor channel lagged behind, skipping {} events", n);
				Ok(stream
					.recv()
					.await
					.expect("could not receive after lagging")
					.into())
			}
		}
	}

	/// await for changed mutex and then next op change
	async fn poll(&self) -> crate::Result<()> {
		Ok(self.0.last_op.lock().await.changed().await?)
	}

	fn stop(&self) -> bool {
		self.0.stop.send(()).is_ok()
	}
}