From 3c62f2d59a7319aef2eedbe0d2c6cc8bb9f87f03 Mon Sep 17 00:00:00 2001
From: Anton Khirnov <anton@khirnov.net>
Date: Sun, 12 Feb 2023 21:56:06 +0000
Subject: rc: show notification on screen backlight changes

---
 rc.lua | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/rc.lua b/rc.lua
index 2bf47ca..28eb8e8 100644
--- a/rc.lua
+++ b/rc.lua
@@ -9,6 +9,8 @@ local beautiful = require("beautiful")
 -- Notification library
 local naughty = require("naughty")
 
+local gio     = require("lgi").Gio
+
 -- local modules
 local bindings   = require("bindings")
 local commondefs = require("commondefs")
@@ -233,3 +235,39 @@ do
             end)
     end
 end
+
+-- show notification on display brightness changes
+local function brightness_stdout(line)
+    local action, device = string.match(line, '^KERNEL%[%d+.%d*%]%s+(%a+)%s+([^%s]+)%s+%(backlight%)$')
+    if action ~= 'change' then
+        return
+    end
+
+    local function readnum(name)
+        local file = gio.File.new_for_path('/sys/' .. device .. '/' .. name)
+        local contents = file:load_contents(nil)
+
+        if contents then
+            contents = string.gsub(contents, "%s$", "")
+            return string.len(contents) > 0 and tonumber(contents) or nil
+        end
+
+        return nil
+    end
+
+    local brightness     = readnum('brightness')
+    local max_brightness = readnum('max_brightness')
+
+    if brightness and max_brightness then
+        utils.notify_singleton(wsp, 'brightness',
+                               { title = 'Brightness',
+                                 text = tostring(100 * brightness // max_brightness) .. '%'})
+    end
+
+    return nil
+end
+local function brightness_exit(reason, code)
+    utils.warn('brightness', 'udevadm monitor exited: %s/%d', reason, code)
+end
+awful.spawn.with_line_callback('udevadm monitor --kernel --subsystem-match=backlight',
+                               { stdout = brightness_stdout, exit = brightness_exit })
-- 
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