feat: restore keyboard backlight on focus loss

scripts/kb-blackout.lua

@@ -5,18 +5,20 @@
     * Listens to pause/playback/core-idle so lights only stay off when media is actively playing.
     * Captures the session's starting brightness, dims via `brightnessctl`, and restores exactly that value when playback stops.
     * Debounces rapid state flips, auto-discovers an LED device (`brightnessctl --list`), and surfaces warnings when Linux, device, or permission prerequisites fail.
+    * Optionally restores the keyboard backlight whenever mpv loses window focus so other apps retain your preferred lighting.
 
   Requirements:
     * Linux + mpv 0.36+ with the bundled Lua 5.2 runtime.
     * `brightnessctl` accessible in PATH or via `brightnessctl_path`, with permission to control the target LED class device.
 
   Configuration:
-    Edit the `config` table below to tune timeouts, restore behavior, minimum brightness, LED device detection, and the `brightnessctl` binary path.
+    Edit the `config` table below to tune timeouts, restore behavior, minimum brightness, LED device detection, focus handling, and the `brightnessctl` binary path.
 ]]
 
 local config = {
   timeout_ms = 3000,
   restore_on_pause = true,
+  restore_on_unfocus = true,
   minimum_brightness = 0,
   led_path = "",
   debounce_ms = 250,
@@ -50,6 +52,7 @@ config.timeout_ms = tonumber(config.timeout_ms) or 3000
 config.minimum_brightness = math.max(0, math.floor(tonumber(config.minimum_brightness) or 0))
 config.debounce_ms = math.max(0, tonumber(config.debounce_ms) or 250)
 config.restore_on_pause = coerce_boolean(config.restore_on_pause, true)
+config.restore_on_unfocus = coerce_boolean(config.restore_on_unfocus, true)
 
 local function seconds(ms)
   return (tonumber(ms) or 0) / 1000
@@ -68,6 +71,7 @@ local state = {
   device_detection_attempted = false,
   first_frame_seen = false,
   pending_timer = false,
+  window_focused = true,
 }
 
 local function detect_keyboard_device()
@@ -388,6 +392,30 @@ local function handle_idle_event(tag)
   restore_backlight(tag or "idle")
 end
 
+local function handle_focus_event(source, focused)
+  local is_focused = not not focused
+  if state.window_focused == is_focused then
+    return
+  end
+  state.window_focused = is_focused
+
+  if not is_focused then
+    emit_intent("focus_lost")
+    cancel_timer()
+    if config.restore_on_unfocus then
+      restore_backlight(source or "focus-lost")
+    else
+      msg.verbose("Focus lost; restore_on_unfocus disabled; keeping lights off.")
+    end
+    return
+  end
+
+  emit_intent("focus_gained")
+  if state.playback_active and not mp.get_property_native("pause") then
+    handle_play_event(source or "focus-gained")
+  end
+end
+
 local function on_pause(_, value)
   if value == nil then
     return
@@ -425,9 +453,17 @@ local function on_filename(_, value)
   end
 end
 
+local function on_focus(_, value)
+  if value == nil then
+    return
+  end
+  handle_focus_event("focus", value)
+end
+
 mp.observe_property("pause", "bool", on_pause)
 mp.observe_property("playback-time", "native", on_playback_time)
 mp.observe_property("filename", "string", on_filename)
+mp.observe_property("focused", "bool", on_focus)
 
 mp.register_event("end-file", function()
   handle_idle_event("end-file")