vanadium/xmobar: make dpi aware

nix/configurations/vanadium/home/xmobar/xmobar.hs

@@ -2,6 +2,48 @@ import Xmobar
 
 import Data.Function ((&))
 import Data.List (intercalate)
+import Data.Map qualified as M
+import System.Process
+
+parseXRDB :: String -> M.Map String String
+parseXRDB = M.fromList . parseXRDBLines . lines
+
+parseXRDBLines :: [String] -> [(String, String)]
+parseXRDBLines = map parseXRDBLine
+
+parseXRDBLine :: String -> (String, String)
+parseXRDBLine s = case break (== ':') s of
+  (k, ':' : v) -> (k, dropWhile (== '\t') v)
+  _ -> error $ "Failed to parse " <> s
+
+-- | Hack to adapt the bar height, fontsize, etc, with the chosen dpi in XRDB
+withDynamicDPI :: Config -> IO Config
+withDynamicDPI cfg = do
+  xrdbConfig <- parseXRDB <$> readCreateProcess (shell "xrdb -query") mempty
+  case xrdbConfig M.!? "Xft.dpi" of
+    Nothing -> pure cfg
+    Just dpiStr ->
+      let
+        dpi = read dpiStr
+
+        -- In case of low DPI:
+        -- * reduce height
+        -- * increase font size
+        isLowDPI = dpi < 120
+
+        updatePosition (BottomH x) = BottomH $ if isLowDPI then 15 else x
+        updatePosition x = x
+
+        updateFontSize x = k <> " " <> v'
+          where
+            (k, ' ' : v) = break (== ' ') x
+            v' = if isLowDPI then "9" else v
+      in
+        pure $ cfg
+          { dpi = dpi
+          , position = updatePosition (position cfg)
+          , font = updateFontSize (font cfg)
+          }
 
 config :: Config
 config =
@@ -99,4 +141,4 @@ minute :: Int -> Int
 minute = (* 60) . second
 
 main :: IO ()
-main = xmobar config
+main = withDynamicDPI config >>= xmobar