Implement sensor status debouncing

This introduces a configurable debouncing delay before which no update
is sent to matrix, which avoids flooding the matrix room with updates
when the door is opened and closed in quick succession. It also allows
to quickly open and close the door without sending notifications.

The debouncing window can be configured in config.yml, see example.

src/main.rs

@@ -57,7 +57,7 @@ enum DoorSensorStatus {
 #[derive(Debug)]
 struct LolOpenerState {
     sensor_status: Option<DoorSensorStatus>,
-    update_pending: bool,
+    pending: Option<(DoorSensorStatus, String)>,
 }
 
 #[tokio::main]
@@ -88,7 +88,7 @@ async fn main() -> anyhow::Result<()> {
 
             let current_state = Arc::new(Mutex::new(LolOpenerState {
                 sensor_status: None,
-                update_pending: false
+                pending: None
             }));
             let current_state = Arc::clone(&current_state);
 
@@ -100,22 +100,43 @@ async fn main() -> anyhow::Result<()> {
                 while let Some((new_status, msg)) = debounce_rx.recv().await {
                     let should_wait = {
                         //XXX: Panic if the lock is poisoned
-                        let state = current_state.lock().unwrap();
-                        !state.update_pending
+                        let mut state = current_state.lock().unwrap();
+                        let should_wait = state.pending.is_none();
+
+                        state.pending = Some((new_status, msg));
+                        should_wait
                     };
 
                     if should_wait {
-                        sleep(Duration::from_secs(debounce_delay)).await;
-                        //XXX: Panic if the lock is poisoned
-                        let mut state = current_state.lock().unwrap();
-                        (*state).update_pending = false;
+                        let tx = bcast_tx.clone();
+                        let rooms = rooms.clone();
+                        let state = current_state.clone();
 
-                        if Some(new_status) != (*state).sensor_status {
-                            debug!("Sending msg {}", msg);
-                            //XXX: Panic if the matrix module can't get the message
-                            bcast_tx.send((msg.into(), rooms.clone())).unwrap();
-                            (*state).sensor_status = Some(new_status);
-                        }
+                        tokio::spawn(async move {
+                            sleep(Duration::from_secs(debounce_delay)).await;
+
+                            let msg = {
+                                //XXX: Panic if the lock is poisoned
+                                let mut state = state.lock().unwrap();
+                                let pending = state.pending.take();
+
+                                match pending {
+                                    Some((status, msg))
+                                        if state.sensor_status.as_ref() != Some(&status) => {
+                                            state.sensor_status = Some(status);
+                                            Some(msg)
+                                        }
+
+                                    _ => None,
+                                }
+                            };
+
+                            if let Some(msg) = msg {
+                                debug!("Sending msg {}", msg);
+                                //XXX: Panic if the matrix module can't get the message
+                                tx.send((msg, rooms)).unwrap();
+                            }
+                        });
                     }
                 }
             });