From 8202594b1d3d45002372e71cc082d37b8ae377ab Mon Sep 17 00:00:00 2001
From: Matthew Flavin <mflavin@mit.edu>
Date: Mon, 8 Mar 2021 00:52:38 -0500
Subject: [PATCH] Added leader functions

---
 CHANGES.md                    |  4 +++
 XMonad/Hooks/ManageHelpers.hs | 55 ++++++++++++++++++++++++++++++++++-
 2 files changed, 58 insertions(+), 1 deletion(-)

diff --git a/CHANGES.md b/CHANGES.md
index f7a4c2a4..1ec594dd 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -311,6 +311,10 @@
 
     - Added `doLower` and `doRaise`
 
+    - Added `findTagLeader`, `ledFrom`, and `shiftToLeader` functions which allow
+      a hook to be created that shifts a window to the workspace of its leader
+      window (according to the WM_CLIENT_LEADER property).
+
   * `XMonad.Util.EZConfig`
 
     - Added support for XF86Bluetooth.
diff --git a/XMonad/Hooks/ManageHelpers.hs b/XMonad/Hooks/ManageHelpers.hs
index 39becb9a..6cc25eec 100644
--- a/XMonad/Hooks/ManageHelpers.hs
+++ b/XMonad/Hooks/ManageHelpers.hs
@@ -35,10 +35,14 @@ module XMonad.Hooks.ManageHelpers (
     isDialog,
     pid,
     transientTo,
+    findTagLeader,
+    ledFrom,
     maybeToDefinite,
     MaybeManageHook,
     transience,
     transience',
+    shiftToLeader,
+    shiftToLeader',
     doRectFloat,
     doFullFloat,
     doCenterFloat,
@@ -169,6 +173,47 @@ transientTo = do
     d <- (liftX . asks) display
     liftIO $ getTransientForHint d w
 
+-- | 'if'' lifted to a monad
+ifM :: Monad m => m Bool -> m a -> m a -> m a
+ifM b t f = do b <- b; if b then t else f
+
+-- | 'find' lifted to a monad
+findM :: Monad m => (a -> m Bool) -> [a] -> m (Maybe a)
+findM p = foldr (\x -> ifM (p x) (pure $ Just x)) (pure Nothing)
+
+-- | 'any' lifted to a monad
+anyM :: Monad m => (a -> m Bool) -> [a] -> m Bool
+anyM p = foldr ((<||>) . p) (pure False)
+
+-- | This function returns the WM_CLIENT_LEADER property for a particular window, 'Just'
+-- the ID if the window sets this property and 'Nothing' otherwise.
+getCL :: Window -> X (Maybe XID)
+getCL = (pure . cp =<<) . getProp32s "WM_CLIENT_LEADER"
+    where
+    cp (Just [x]) = Just (fromIntegral x)
+    cp _ = Nothing
+
+-- | For a given window, the findTagLeader function attempts to find the 'WorkspaceId' 
+-- of the first window, aside from itself, that sets the same WM_CLIENT_LEADER property. 
+-- It returns 'Just' the workspace tag if the window sets this property and a matching 
+-- window can be found within the given 'StackSet', and 'Nothing' otherwise.
+findTagLeader ::  Window -> W.StackSet i l Window s sd -> X (Maybe i)
+findTagLeader a = fmap getTag . (findM $ has . W.stack) . W.workspaces
+    where
+    has Nothing = pure False
+    has (Just (W.Stack t l r)) = isLeader t  <||> anyM isLeader l <||> anyM isLeader r 
+    isLeader w = do 
+        k <- getCL w
+        j <- getCL a
+        return $ k /= Nothing && w /= a && j == k
+    getTag Nothing = Nothing
+    getTag (Just (W.Workspace i l a)) = Just i
+
+-- | A predicate to check whether a window has a leader. It holds the result which might 
+-- be the workspace tag of the window that leads it or 'Nothing' if one cannot be found.
+ledFrom :: Query (Maybe WorkspaceId)
+ledFrom = ask >>= liftX . withWindowSet . findTagLeader
+
 -- | A convenience 'MaybeManageHook' that will check to see if a window
 -- is transient, and then move it to its parent.
 transience :: MaybeManageHook
@@ -181,11 +226,19 @@ transience = transientTo </=? Nothing -?>> move
 transience' :: ManageHook
 transience' = maybeToDefinite transience
 
+-- | A convenience 'MaybeManageHook' that will check to see if a window has a leader,
+-- and then move it to the workspace of the leader.
+shiftToLeader :: MaybeManageHook
+shiftToLeader = ledFrom </=? Nothing -?>> maybe idHook doShift
+
+-- | 'shiftToLeader' set to a 'ManageHook'
+shiftToLeader' :: ManageHook
+shiftToLeader' = maybeToDefinite shiftToLeader
+
 -- | converts 'MaybeManageHook's to 'ManageHook's
 maybeToDefinite :: (Monoid a, Functor m) => m (Maybe a) -> m a
 maybeToDefinite = fmap (fromMaybe mempty)
 
-
 -- | Floats the new window in the given rectangle.
 doRectFloat :: W.RationalRect  -- ^ The rectangle to float the window in. 0 to 1; x, y, w, h.
             -> ManageHook