feat: implement support for monitoring D-Bus signals

lua/auto-dark-mode/init.lua

@@ -54,6 +54,8 @@ M.state = {
 	system = nil,
 	---@type table
 	query_command = {},
+	---@type table
+	monitor_command = {},
 }
 
 ---@return nil
@@ -92,6 +94,14 @@ M.init = function()
 			"string:org.freedesktop.appearance",
 			"string:color-scheme",
 		}
+
+		if vim.fn.executable("dbus-monitor") ~= 0 then
+			M.state.monitor_command = {
+				"dbus-monitor",
+				"--session",
+				"type=signal,interface=org.freedesktop.portal.Settings,member=SettingChanged,path=/org/freedesktop/portal/desktop,arg0='org.freedesktop.appearance',arg1='color-scheme'",
+			}
+		end
 	elseif M.state.system == "Windows_NT" or M.state.system == "WSL" then
 		local reg = "reg.exe"
 

lua/auto-dark-mode/interval.lua

@@ -16,9 +16,9 @@ local uv = vim.uv or vim.loop
 ---@return Appearance?
 local function parse_query_response(stdout, stderr)
 	if M.state.system == "Linux" then
-        if stderr ~= "" then
-            return nil;
-        end
+		if stderr ~= "" then
+			return nil
+		end
 
 		-- https://github.com/flatpak/xdg-desktop-portal/blob/c0f0eb103effdcf3701a1bf53f12fe953fbf0b75/data/org.freedesktop.impl.portal.Settings.xml#L32-L46
 		-- 0: no preference
@@ -67,6 +67,49 @@ local function sync_theme(appearance)
 	end
 end
 
+-- Uses a subprocess to monitor the system for the current dark mode setting.
+-- The callback is called with the plaintext stdout response of the query.
+---@param callback? fun(stdout: string, stderr: string): nil
+---@return nil
+M.monitor_dark_mode = function(callback)
+	-- if no callback is provided, use a no-op
+	callback = callback or function() end
+
+	if vim.system then
+		vim.system(M.state.monitor_command, {
+			text = true,
+			stdout = function(_, data)
+				if string.match(data, "uint32") then
+					-- check if this was a signal update with a new value,
+					-- as otherwise the fallback option will be incorrectly triggered
+					callback(data, "")
+				end
+			end,
+			stderr = function(_, data)
+				callback("", data)
+			end,
+		})
+	else
+		-- Legacy implementation using `vim.fn.jobstart` instead of `vim.system`,
+		-- for use in neovim <0.10.0
+		vim.fn.jobstart(M.state.monitor_command, {
+			on_stdout = function(_, data, _)
+				data = table.concat(data, "")
+
+				if string.match(data, "uint32") then
+					-- check if this was a signal update with a new value,
+					-- as otherwise the fallback option will be incorrectly triggered
+					callback(data, "")
+				end
+			end,
+			on_stderr = function(_, data, _)
+				data = table.concat(data, "")
+				callback("", data)
+			end,
+		})
+	end
+end
+
 -- Uses a subprocess to query the system for the current dark mode setting.
 -- The callback is called with the plaintext stdout response of the query.
 ---@param callback? fun(stdout: string, stderr: string): nil
@@ -151,7 +194,12 @@ M.start = function(options, state)
 	-- act as if the timer has finished once to instantly sync on startup
 	timer_callback()
 
-	M.start_timer()
+	-- if the system supports monitoring, prefer that over polling updates
+	if next(M.state.monitor_command) ~= nil then
+		M.monitor_dark_mode(M.parse_callback)
+	else
+		M.start_timer()
+	end
 end
 
 return M