From b2319c8084d34edb85e0fee4ca7edcdee0c8aeed Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Roman=20Smr=C5=BE?= <roman.smrz@seznam.cz>
Date: Mon, 1 Jun 2026 20:52:01 +0200
Subject: Postpone flushing terminal when replacing lines

---
 main/Main.hs     |  2 +-
 main/Terminal.hs | 33 ++++++++++++++++++++++++++-------
 2 files changed, 27 insertions(+), 8 deletions(-)

diff --git a/main/Main.hs b/main/Main.hs
index 4a85f4e..8d7cc08 100644
--- a/main/Main.hs
+++ b/main/Main.hs
@@ -418,7 +418,7 @@ interactiveLoop st opts = withTerminal commandCompletion $ \term -> do
     _ <- liftIO $ do
         tzone <- getCurrentTimeZone
         let self = finalOwner $ headLocalIdentity erebosHead
-        watchDirectMessageThreads erebosHead $ \prev cur -> do
+        watchDirectMessageThreads erebosHead $ \prev cur -> holdFlush term $ do
             let ( remove, messages ) = dmThreadToListChange prev cur
             when (remove > 0) $ do
                 modifyMVar_ currentLinesVar $ \clines -> if
diff --git a/main/Terminal.hs b/main/Terminal.hs
index 53814f9..5b814f8 100644
--- a/main/Terminal.hs
+++ b/main/Terminal.hs
@@ -5,6 +5,7 @@ module Terminal (
     Terminal,
     hasTerminalUI,
     withTerminal,
+    holdFlush,
     setPrompt,
     setPromptStatus,
     showPrompt, hidePrompt,
@@ -59,6 +60,7 @@ data Terminal = Terminal
     , termHistoryPos :: TVar Int
     , termHistoryStash :: TVar ( String, String )
     , termBottomIndex :: TVar Int
+    , termHoldFlush :: TVar Int
     }
 
 data TerminalLine = TerminalLine
@@ -108,6 +110,7 @@ initTerminal termCompletionFunc = do
     termHistoryPos <- newTVarIO 0
     termHistoryStash <- newTVarIO ( "", "" )
     termBottomIndex <- newTVarIO 0
+    termHoldFlush <- newTVarIO 0
     return Terminal {..}
 
 bracketSet :: IO a -> (a -> IO b) -> a -> IO c -> IO c
@@ -123,6 +126,22 @@ withTerminal compl act = do
             act term
 
 
+termFlush :: Terminal -> IO ()
+termFlush Terminal {..} = do
+    join $ atomically $ do
+        readTVar termHoldFlush >>= \case
+            0 -> return $ hFlush stdout
+            _ -> return $ return ()
+
+holdFlush :: Terminal -> IO a -> IO a
+holdFlush term@Terminal {..} act = do
+    atomically $ writeTVar termHoldFlush . (+ 1) =<< readTVar termHoldFlush
+    x <- act
+    atomically $ writeTVar termHoldFlush . subtract 1 =<< readTVar termHoldFlush
+    termFlush term
+    return x
+
+
 putAnsi :: AnsiText -> IO ()
 putAnsi = T.putStr . fromAnsiText
 
@@ -201,7 +220,7 @@ getInputLine term@Terminal {..} handleResult = do
                             writeTVar termInput ( pre', post )
                             getCurrentPromptLine term
                         putAnsi $ "\r" <> prompt
-                        hFlush stdout
+                        termFlush term
 
                 termCompletionFunc ( T.pack pre, T.pack post ) >>= \case
 
@@ -310,7 +329,7 @@ getInputLine term@Terminal {..} handleResult = do
             str <- atomically $ f =<< readTVar termInput
             when (termAnsi && not (T.null $ fromAnsiText str)) $ do
                 putAnsi str
-                hFlush stdout
+                termFlush term
         go
 
 
@@ -332,7 +351,7 @@ redrawPrompt term = do
     promptLine <- getCurrentPromptLine term
     return $ do
         putAnsi $ "\r\ESC[K" <> promptLine
-        hFlush stdout
+        termFlush term
 
 setPrompt :: Terminal -> FormattedText -> IO ()
 setPrompt Terminal { termAnsi = False } _ = do
@@ -403,7 +422,7 @@ printLine tlTerminal@Terminal {..} str = do
             writeTVar termBottomIndex $ bindex + tlLineCount
             return bindex
 
-        hFlush stdout
+        termFlush tlTerminal
         return TerminalLine {..}
 
 updateLine :: TerminalLine -> FormattedText -> IO ()
@@ -443,19 +462,19 @@ printBottomLines term@Terminal {..} str = do
             withMVar termLock $ \_ -> do
                 atomically $ writeTVar termBottomLines blines
                 drawBottomLines term
-                hFlush stdout
+                termFlush term
 
 clearBottomLines :: Terminal -> IO ()
 clearBottomLines Terminal { termAnsi = False } = do
     return ()
-clearBottomLines Terminal {..} = do
+clearBottomLines term@Terminal {..} = do
     withMVar termLock $ \_ -> do
         atomically (readTVar termBottomLines) >>= \case
             []  -> return ()
             _:_ -> do
                 atomically $ writeTVar termBottomLines []
                 putStr $ "\ESC[s\n\ESC[J\ESC[u"
-                hFlush stdout
+                termFlush term
 
 drawBottomLines :: Terminal -> IO ()
 drawBottomLines Terminal {..} = do
-- 
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