Install battery applet, and make it work in the panel

applets/cosmic-applet-battery/src/backlight.rs

@@ -0,0 +1,88 @@
+// TODO: use udev to monitor for brightness changes?
+// How should key bindings be handled? Need something like gnome-settings-daemon?
+
+use std::{
+    fs::{self, File},
+    io::{self, Read},
+    os::unix::ffi::OsStrExt,
+    path::Path,
+    str::{self, FromStr},
+};
+
+const BACKLIGHT_SYSDIR: &str = "/sys/class/backlight";
+
+#[zbus::dbus_proxy(
+    default_service = "org.freedesktop.login1",
+    interface = "org.freedesktop.login1.Session",
+    default_path = "/org/freedesktop/login1/session/auto"
+)]
+trait LogindSession {
+    fn set_brightness(&self, subsystem: &str, name: &str, brightness: u32) -> zbus::Result<()>;
+}
+
+#[derive(Clone)]
+pub struct Backlight(String);
+
+impl Backlight {
+    pub fn brightness(&self) -> Option<u32> {
+        self.prop("brightness")
+    }
+
+    // XXX cache value. Async?
+    pub fn max_brightness(&self) -> Option<u32> {
+        self.prop("max_brightness")
+    }
+
+    pub async fn set_brightness(
+        &self,
+        session: &LogindSessionProxy<'_>,
+        value: u32,
+    ) -> zbus::Result<()> {
+        session.set_brightness("backlight", &self.0, value).await
+    }
+
+    fn prop<T: FromStr>(&self, name: &str) -> Option<T> {
+        let path = Path::new(BACKLIGHT_SYSDIR).join(&self.0).join(name);
+        let mut file = File::open(path).ok()?;
+        let mut s = String::new();
+        file.read_to_string(&mut s).ok()?;
+        s.trim().parse().ok()
+    }
+}
+
+// Choose backlight with most "precision". This is what `light` does.
+pub fn backlight() -> io::Result<Option<Backlight>> {
+    let mut best_backlight = None;
+    let mut best_max_brightness = 0;
+    for i in fs::read_dir(BACKLIGHT_SYSDIR)? {
+        if let Ok(filename) = str::from_utf8(i?.file_name().as_bytes()) {
+            let backlight = Backlight(filename.to_string());
+            if let Some(max_brightness) = backlight.max_brightness() {
+                if max_brightness > best_max_brightness {
+                    best_backlight = Some(backlight);
+                    best_max_brightness = max_brightness;
+                }
+            }
+        }
+    }
+    Ok(best_backlight)
+}
+
+/*
+// TODO: Cache device, max_brightness, etc.
+async fn set_display_brightness(brightness: f64) -> io::Result<()> {
+    if let Some(backlight) = backlight()? {
+        if let Some(max_brightness) = backlight.max_brightness() {
+            let value = brightness.clamp(0., 1.) * (max_brightness as f64);
+            let value = value.round() as u32;
+            let connection = zbus::Connection::system().await?;
+            if let Ok(session) = LogindSessionProxy::builder(&connection).build().await {
+                backlight.set_brightness(&session, value).await;
+            }
+        }
+    }
+    Ok(())
+}
+*/
+
+// TODO: keyboard backlight