From ec96ec469e9dff06bc503366ff7e3022c595d8f7 Mon Sep 17 00:00:00 2001
From: Guy Gastineau <strings.stringsandstrings@gmail.com>
Date: Tue, 14 Sep 2021 13:05:49 -0400
Subject: Add the QueueReader plugin.

  * A queue reader for xmobar using `TQueue a` from `stm`.
    This is a flexible and performat solution for sharing
    data between arbitrary haskell and xmobar.
  * I am not sure if I did the haddocks correctly.
---
 src/Xmobar.hs                     |  2 ++
 src/Xmobar/Plugins/QueueReader.hs | 50 +++++++++++++++++++++++++++++++++++++++
 xmobar.cabal                      |  1 +
 3 files changed, 53 insertions(+)
 create mode 100644 src/Xmobar/Plugins/QueueReader.hs

diff --git a/src/Xmobar.hs b/src/Xmobar.hs
index f37f065..28ef354 100644
--- a/src/Xmobar.hs
+++ b/src/Xmobar.hs
@@ -33,6 +33,7 @@ module Xmobar (xmobar
 #endif
               , module Xmobar.Plugins.EWMH
               , module Xmobar.Plugins.HandleReader
+              , module Xmobar.Plugins.QueueReader
               , module Xmobar.Plugins.Kbd
               , module Xmobar.Plugins.Locks
 #ifdef INOTIFY
@@ -60,6 +61,7 @@ import Xmobar.Plugins.DateZone
 #endif
 import Xmobar.Plugins.EWMH
 import Xmobar.Plugins.HandleReader
+import Xmobar.Plugins.QueueReader
 import Xmobar.Plugins.Kbd
 import Xmobar.Plugins.Locks
 #ifdef INOTIFY
diff --git a/src/Xmobar/Plugins/QueueReader.hs b/src/Xmobar/Plugins/QueueReader.hs
new file mode 100644
index 0000000..cf60c1d
--- /dev/null
+++ b/src/Xmobar/Plugins/QueueReader.hs
@@ -0,0 +1,50 @@
+{-# LANGUAGE RecordWildCards #-}
+module Xmobar.Plugins.QueueReader
+  (QueueReader (..)
+  ) where
+
+import Xmobar.Run.Exec (Exec (..))
+
+import Control.Monad (forever)
+import qualified Control.Concurrent.STM as STM
+
+-- | A 'QueueReader' displays data from an 'TQueue a' where
+-- the data items 'a' are rendered by a user supplied function.
+--
+-- Like the 'HandleReader' plugin this is only useful if you are
+-- running @xmobar@ from other Haskell code.  You should create a
+-- new @TQueue a@ and pass it to this plugin.
+--
+-- @
+-- main :: IO
+-- main = do
+--   q <- STM.newQueueIO @String
+--   bar <- forkIO $ xmobar conf
+--     { commands = Run (QueueReader q id "Queue") : commands conf }
+--   STM.atomically $ STM.writeTQueue q "Some Message"
+-- @
+data QueueReader a
+  = QueueReader
+  { qQueue    :: STM.TQueue a
+  , qShowItem :: a -> String
+  , qName :: String
+  }
+
+-- | This cannot be read back.
+instance Show (QueueReader a) where
+  -- | Only show the name/alias for the queue reader.
+  show q = "QueueReader " <> qName q
+
+-- | WARNING: This read instance will throw an exception if used! It is
+-- only implemented, because it is required by 'Xmobar.Run` in 'Xmobar.commands'.
+instance Read (QueueReader a) where
+  -- | Throws an 'error'!
+  readsPrec = error "QueueReader: instance is a stub"
+
+-- | Async queue/channel reading.
+instance Exec (QueueReader a) where
+  -- | Read from queue as data arrives.
+  start QueueReader{..} cb =
+    forever (STM.atomically (qShowItem <$> STM.readTQueue qQueue) >>= cb)
+
+  alias = qName
diff --git a/xmobar.cabal b/xmobar.cabal
index 5c16dc1..7bc6a61 100644
--- a/xmobar.cabal
+++ b/xmobar.cabal
@@ -140,6 +140,7 @@ library
                    Xmobar.Plugins.Date,
                    Xmobar.Plugins.EWMH,
                    Xmobar.Plugins.HandleReader,
+                   Xmobar.Plugins.QueueReader,
                    Xmobar.Plugins.PipeReader,
                    Xmobar.Plugins.MarqueePipeReader,
                    Xmobar.Plugins.StdinReader,
-- 
cgit v1.2.3