battery eta smoothing

crates/services/src/battery.rs

@@ -15,6 +15,11 @@ pub const NAMESPACE: &str = "battery.";
 
 /// How long to wait before retrying when UPower is unreachable.
 const RETRY: Duration = Duration::from_secs(30);
+/// EMA weight for raw UPower estimates; lower = smoother but laggier.
+// ponytail: fixed alpha, make configurable if laggy/jittery on real hardware.
+const ETA_ALPHA: f64 = 0.3;
+/// Minimum change before republishing ETA; matches the minute-resolution display.
+const ETA_DEADBAND_SECS: u64 = 60;
 
 /// UPower device states (`org.freedesktop.UPower.Device.State`).
 const CHARGING: u32 = 1;
@@ -34,8 +39,9 @@ impl BatteryService {
             iced::stream::channel(0, move |mut sender: mpsc::Sender<Wire>| async move {
                 tracing::info!(key, "battery service started");
                 let mut last: Option<(i32, BatteryStatus, i64, i64)> = None;
+                let mut eta_filter = EtaFilter::default();
                 loop {
-                    match serve(&mut sender, key, &mut last).await {
+                    match serve(&mut sender, key, &mut last, &mut eta_filter).await {
                         // Subscriber gone: stop the service.
                         Ok(false) => return,
                         Ok(true) => tracing::debug!(key, "upower stream ended; reconnecting"),
@@ -54,12 +60,13 @@ async fn serve(
     sender: &mut mpsc::Sender<Wire>,
     key: &'static str,
     last: &mut Option<(i32, BatteryStatus, i64, i64)>,
+    eta_filter: &mut EtaFilter,
 ) -> Result<bool, zbus::Error> {
     let conn = zbus::Connection::system().await?;
     let display = UPowerProxy::new(&conn).await?.get_display_device().await?;
     let device = DeviceProxy::builder(&conn).path(display)?.build().await?;
 
-    if !emit(sender, key, last, read(&device).await?).await {
+    if !emit(sender, key, last, eta_filter, read(&device).await?).await {
         return Ok(false);
     }
 
@@ -77,7 +84,7 @@ async fn serve(
             Some(change) = time_to_full.next() => (percent, status, change.get().await?, to_empty),
             else => return Ok(true),
         };
-        if !emit(sender, key, last, current).await {
+        if !emit(sender, key, last, eta_filter, current).await {
             return Ok(false);
         }
     }
@@ -89,6 +96,7 @@ async fn emit(
     sender: &mut mpsc::Sender<Wire>,
     key: &'static str,
     last: &mut Option<(i32, BatteryStatus, i64, i64)>,
+    eta_filter: &mut EtaFilter,
     (percent, status, to_full, to_empty): (i32, BatteryStatus, i64, i64),
 ) -> bool {
     let mut events = Vec::new();
@@ -100,11 +108,9 @@ async fn emit(
         tracing::debug!(key, ?status, "publishing battery status");
         events.push(BatteryEvent::StatusChanged(status));
     }
-    let old_eta = last.map(|(_, s, f, e)| eta(s, f, e)).unwrap_or_default();
-    let new_eta = eta(status, to_full, to_empty);
-    if old_eta != new_eta {
-        tracing::debug!(key, ?new_eta, "publishing battery eta");
-        events.push(BatteryEvent::EtaChanged(new_eta));
+    if let Some(smoothed) = eta_filter.update(status, to_full, to_empty) {
+        tracing::debug!(key, ?smoothed, "publishing battery eta");
+        events.push(BatteryEvent::EtaChanged(smoothed));
     }
     *last = Some((percent, status, to_full, to_empty));
     for event in events {
@@ -127,6 +133,60 @@ async fn read(device: &DeviceProxy<'_>) -> Result<(i32, BatteryStatus, i64, i64)
     ))
 }
 
+/// Low-pass + deadband filter for UPower's jittery time estimates.
+/// `update` returns `Some` only when the module should be notified.
+#[derive(Default)]
+struct EtaFilter {
+    smooth: Option<f64>,
+    status: Option<BatteryStatus>,
+    published: Option<Option<u64>>,
+}
+
+impl EtaFilter {
+    fn update(
+        &mut self,
+        status: BatteryStatus,
+        to_full: i64,
+        to_empty: i64,
+    ) -> Option<Option<u64>> {
+        let raw = eta(status, to_full, to_empty);
+        let Some(raw) = raw else {
+            self.smooth = None;
+            self.status = Some(status);
+            // First run with no estimate: nothing to report (matches unfiltered behavior).
+            let changed = self.published.is_some_and(|p| p.is_some());
+            self.published = Some(None);
+            return changed.then_some(None);
+        };
+        // Estimate source switches with charge state, so past smoothing is stale.
+        let reset = self.status != Some(status) || self.smooth.is_none();
+        self.status = Some(status);
+        let smooth = if reset {
+            raw as f64
+        } else {
+            ETA_ALPHA * raw as f64 + (1.0 - ETA_ALPHA) * self.smooth.unwrap_or(raw as f64)
+        };
+        self.smooth = Some(smooth);
+        let candidate = smooth.round() as u64;
+        match self.published {
+            // First sample: publish immediately.
+            None => {
+                self.published = Some(Some(candidate));
+                Some(Some(candidate))
+            }
+            Some(published) => {
+                let drift = published.map_or(u64::MAX, |p| p.abs_diff(candidate));
+                if reset || drift >= ETA_DEADBAND_SECS {
+                    self.published = Some(Some(candidate));
+                    Some(Some(candidate))
+                } else {
+                    None
+                }
+            }
+        }
+    }
+}
+
 /// Seconds until full while charging, or until empty while discharging.
 /// UPower reports 0 when there is no estimate, and neither state applies
 /// once full, empty, or unknown — all of those surface as `None`.
@@ -182,3 +242,48 @@ trait Device {
     #[zbus(property)]
     fn time_to_full(&self) -> zbus::Result<i64>;
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const DIS: BatteryStatus = BatteryStatus::Discharging;
+
+    #[test]
+    fn jitter_within_deadband_is_suppressed() {
+        let mut f = EtaFilter::default();
+        assert_eq!(f.update(DIS, 0, 3600), Some(Some(3600)));
+        assert_eq!(f.update(DIS, 0, 3610), None);
+        assert_eq!(f.update(DIS, 0, 3590), None);
+    }
+
+    #[test]
+    fn large_step_publishes_smoothed_value() {
+        let mut f = EtaFilter::default();
+        assert_eq!(f.update(DIS, 0, 3600), Some(Some(3600)));
+        // EMA: 0.3*1800 + 0.7*3600 = 3060, drift 540 >= 60.
+        assert_eq!(f.update(DIS, 0, 1800), Some(Some(3060)));
+    }
+
+    #[test]
+    fn status_flip_resets_and_publishes() {
+        let mut f = EtaFilter::default();
+        assert_eq!(f.update(DIS, 0, 3600), Some(Some(3600)));
+        assert_eq!(f.update(BatteryStatus::Charging, 1200, 0), Some(Some(1200)));
+    }
+
+    #[test]
+    fn loss_and_return_of_estimate_publishes() {
+        let mut f = EtaFilter::default();
+        assert_eq!(f.update(DIS, 0, 3600), Some(Some(3600)));
+        assert_eq!(f.update(DIS, 0, 0), Some(None));
+        assert_eq!(f.update(DIS, 0, 0), None);
+        assert_eq!(f.update(DIS, 0, 3500), Some(Some(3500)));
+    }
+
+    #[test]
+    fn first_run_without_estimate_stays_silent() {
+        let mut f = EtaFilter::default();
+        assert_eq!(f.update(BatteryStatus::Full, 0, 0), None);
+    }
+}