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

@@ -24,7 +24,8 @@ mod matrix;
 mod mqtt;
 
 use tokio::{
-    sync::{Notify, broadcast},
+    sync::{Notify, broadcast, mpsc},
+    time::{sleep, Duration},
     task::JoinHandle,
 };
 
@@ -48,11 +49,16 @@ struct Args {
     config: String,
 }
 
-#[derive(PartialEq)]
-enum LolOpenerStatus {
+#[derive(PartialEq, Clone, Copy, Debug)]
+enum DoorSensorStatus {
     Open,
     Closed,
 }
+#[derive(Debug)]
+struct LolOpenerState {
+    sensor_status: Option<DoorSensorStatus>,
+    pending: Option<(DoorSensorStatus, String)>,
+}
 
 #[tokio::main]
 async fn main() -> anyhow::Result<()> {
@@ -80,25 +86,75 @@ async fn main() -> anyhow::Result<()> {
             matrix_ready.notified().await;
             info!("Matrix is ready");
 
-            let current_status = Arc::new(Mutex::new(None));
-            let current_status = Arc::clone(&current_status);
+            let current_state = Arc::new(Mutex::new(LolOpenerState {
+                sensor_status: None,
+                pending: None
+            }));
+            let current_state = Arc::clone(&current_state);
+
+            let (debounce_tx, mut debounce_rx) = mpsc::unbounded_channel::<(DoorSensorStatus, String)>();
+            let debounce_delay = config.debounce_delay;
+            let rooms = config.rooms.clone();
+            let handle = tokio::spawn(async move {
+
+                while let Some((new_status, msg)) = debounce_rx.recv().await {
+                    let should_wait = {
+                        //XXX: Panic if the lock is poisoned
+                        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 {
+                        let tx = bcast_tx.clone();
+                        let rooms = rooms.clone();
+                        let state = current_state.clone();
+
+                        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();
+                            }
+                        });
+                    }
+                }
+            });
 
             let mut mqtt = MQTT::new(config.mqtt.clone()).await;
             mqtt.subscribe(move |status: StatusMessage| {
                 let (new_status, msg) = match status {
-                    StatusMessage { contact: true, .. } => (Some(LolOpenerStatus::Closed), "🔴 Le LOL est fermé :("),
-                    StatusMessage { contact: false, .. } => (Some(LolOpenerStatus::Open), "🟢 Le LOL est ouvert :)"),
+                    StatusMessage { contact: true, .. } => (DoorSensorStatus::Closed, "🔴 Le LOL est fermé :("),
+                    StatusMessage { contact: false, .. } => (DoorSensorStatus::Open, "🟢 Le LOL est ouvert :)"),
                 };
 
-                //XXX: Panic if the lock is poisoned (why would that happen?)
-                let mut current_status = current_status.lock().unwrap();
-                if new_status != *current_status {
-                    debug!("Sending msg {}", msg);
-                    //XXX: Panic if the matrix module can't get the message
-                    bcast_tx.send((msg.into(), config.rooms.clone())).unwrap();
-                    *current_status = new_status;
-                }
+                //XXX: Panic if the channel is closed
+                debounce_tx.send((new_status, String::from(msg))).unwrap();
+
             }).await.unwrap(); //XXX: Panic if the mqtt broker fails
+
+            handle.abort();
+            handle.await.unwrap();
         })
     };