rewrite it in haskell

packages/git-changes.nix

@@ -2,6 +2,7 @@
 # `git diff HEAD` to show both staged and unstaged changes. Useful for
 # monitoring code changes made by LLMs in real-time without manually restarting
 # the diff viewer.
+
 { writers, haskellPackages, git, coreutils, ... }:
 
 writers.writeHaskellBin "git-changes"
@@ -16,48 +17,69 @@ writers.writeHaskellBin "git-changes"
   import System.FSNotify
   import Control.Concurrent
   import Control.Monad
-  import System.Process
+  import System.Process (system)
   import System.IO
   import Data.List (isInfixOf)
+  import System.Exit (ExitCode(..))
+  import Control.Exception (catch, SomeException)
 
   loadFromBins ["${git}", "${coreutils}"]
 
   main :: IO ()
   main = do
     hSetBuffering stdout NoBuffering
+    hSetBuffering stderr NoBuffering
+    
+    hPutStrLn stderr "[git-changes] Starting..."
+    
+    -- Use a simple approach: just run git diff in foreground, restart when files change
+    runningRef <- newMVar False
     
-    -- Start initial git diff
-    diffRef <- newMVar Nothing
     let runDiff = do
-          -- Kill previous diff if running
-          oldProc <- takeMVar diffRef
-          case oldProc of
-            Just ph -> do
-              terminateProcess ph
-              void $ waitForProcess ph
-            Nothing -> return ()
-          
-          -- Start new git diff
-          ph <- spawnCommand "${git}/bin/git diff HEAD"
-          putMVar diffRef (Just ph)
+          -- Don't restart if already running
+          isRunning <- tryTakeMVar runningRef
+          case isRunning of
+            Just True -> do
+              hPutStrLn stderr "[git-changes] Diff already running, skipping..."
+              putMVar runningRef True
+              return ()
+            _ -> do
+              putMVar runningRef True
+              hPutStrLn stderr "[git-changes] Running git diff..."
+              
+              -- Run git diff - this blocks until it exits
+              exitCode <- system "${git}/bin/git diff HEAD"
+              
+              void $ takeMVar runningRef
+              hPutStrLn stderr $ "[git-changes] Git diff exited with: " ++ show exitCode
+              
+              -- If user quit successfully, exit the program
+              case exitCode of
+                ExitSuccess -> error "User quit"
+                _ -> return ()
     
-    -- Run initial diff
-    runDiff
+    -- Run initial diff in a thread
+    diffThread <- forkIO runDiff
     
-    -- Watch for file changes
-    withManager $ \mgr -> do
+    -- Fork a thread to watch for file changes
+    hPutStrLn stderr "[git-changes] Starting file watcher..."
+    void $ forkIO $ withManager $ \mgr -> do
       _ <- watchTree
         mgr
         "."
-        (\event -> case event of
-          _ -> let path = eventPath event
-               in not (".git" `isInfixOf` path)
-        )
-        (\_ -> do
-          putStrLn "File changed, restarting diff..."
-          runDiff
-        )
+        (\event -> let path = eventPath event
+                   in not (".git" `isInfixOf` path))
+        (\event -> do
+          hPutStrLn stderr $ "[git-changes] File changed: " ++ eventPath event
+          -- Kill the current diff thread
+          killThread diffThread
+          void $ takeMVar runningRef
+          -- Start a new one
+          void $ forkIO runDiff)
       
-      -- Keep running
       forever $ threadDelay 1000000
+    
+    hPutStrLn stderr "[git-changes] Waiting for user to quit..."
+    -- Wait for the diff thread to finish
+    threadDelay maxBound
 ''