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+-----------------------------------------------------------------------------
+-- |
+-- Module      :  XMonad.Hooks.DynamicProperty
+-- Copyright   :  (c) Brandon S Allbery, 2015
+-- License     :  BSD3-style (see LICENSE)
+--
+-- Maintainer  :  allbery.b@gmail.com
+-- Stability   :  unstable
+-- Portability :  not portable
+--
+-- Module to apply a ManageHook to an already-mapped window when a property
+-- changes. This would commonly be used to match browser windows by title,
+-- since the final title will only be set after (a) the window is mapped,
+-- (b) its document has been loaded, (c) all load-time scripts have run.
+-- (Don't blame browsers for this; it's inherent in HTML and the DOM. And
+-- changing title dynamically is explicitly permitted by ICCCM and EWMH;
+-- you don't really want to have your editor window umapped/remapped to
+-- show the current document and modified state in the titlebar, do you?)
+--
+-- This is a handleEventHook that triggers on a PropertyChange event. It
+-- currently ignores properties being removed, in part because you can't
+-- do anything useful in a ManageHook involving nonexistence of a property.
+--
+-----------------------------------------------------------------------------
+
+module XMonad.Hooks.DynamicProperty where
+
+import XMonad
+import Data.Monoid
+import Control.Applicative
+import Control.Monad (when)
+
+-- |
+-- Run a 'ManageHook' when a specific property is changed on a window. Note
+-- that this will run on any window which changes the property, so you should
+-- be very specific in your 'MansgeHook' matching (lots of windows change
+-- their titles on the fly!):
+--
+-- dynamicPropertyChange "WM_NAME" (className =? "Iceweasel" <&&> title =? "whatever" --> doShift "2")
+-- 
+-- Note that the fixity of (-->) won't allow it to be mixed with ($), so you
+-- can't use the obvious $ shorthand.
+--
+-- > dynamicPropertyChange "WM_NAME" $ title =? "Foo" --> doFloat -- won't work!
+--
+-- Consider instead phrasing it like any
+-- other 'ManageHook':
+--
+-- >      , handleEventHook = dynamicPropertyChange "WM_NAME" myDynHook <+> handleEventHook baseConfig
+-- > 
+-- >    {- ... -}
+-- > 
+-- >    myDynHook = composeAll [...]
+--
+dynamicPropertyChange :: String -> ManageHook -> Event -> X All
+dynamicPropertyChange prop hook PropertyEvent { ev_window = w, ev_atom = a, ev_propstate = ps } = do
+  pa <- getAtom prop
+  when (ps == propertyNewValue && a == pa) $ do
+    g <- appEndo <$> userCodeDef (Endo id) (runQuery hook w)
+    windows g
+  return (All False) -- so anything else also processes it
+dynamicPropertyChange _ _ _ = return (All False)
+
+-- | A shorthand for the most common case, dynamic titles
+dynamicTitle :: ManageHook -> Event -> X All
+-- strictly, this should also check _NET_WM_NAME. practically, both will
+-- change and each gets its own PropertyEvent, so we'd need to record that
+-- we saw the event for that window and ignore the second one. Instead, just
+-- trust that nobody sets only _NET_WM_NAME. (I'm sure this will prove false,
+-- since there's always someone who can't bother being compliant.)
+dynamicTitle = dynamicPropertyChange "WM_NAME"