[scan for device
Evan Martin <martine@danga.com>**20060216085150] {
hunk ./MPDMate.hs 8
-file = "/dev/input/event3"
-
hunk ./MPDMate.hs 21
+main :: IO ()
hunk ./MPDMate.hs 23
-  name <- PowerMate.getName file
-  putStrLn name
+  powermate_device <- PowerMate.searchForDevice
+  case powermate_device of
+    Nothing  -> return ()
+    Just pmd -> do
+      mpd <- MPD.connect "localhost" 6600
hunk ./MPDMate.hs 29
-  mpd <- MPD.connect "localhost" 6600
-
-  handle_pm <- openBinaryFile file ReadWriteMode
-  loop mpd $ \mpd -> do
-    event <- PowerMate.readEventWithSkip handle_pm Nothing
-    (do maybe (return ()) (processEvent mpd) event
-        return mpd)
-       `catch` \e -> do
-         print $ ioeGetErrorString e
-         MPD.reconnect mpd
+      handle_pm <- openBinaryFile pmd ReadWriteMode
+      loop mpd $ \mpd -> do
+        event <- PowerMate.readEventWithSkip handle_pm Nothing
+        (do maybe (return ()) (processEvent mpd) event
+            return mpd)
+           `catch` \e -> do
+             print $ ioeGetErrorString e
+             MPD.reconnect mpd
+      return ()
hunk ./PowerMate.hsc 3
-  getName,
+  getUSBName,
+  searchForDevice,
hunk ./PowerMate.hsc 19
+import List (isPrefixOf, find)
+import Control.Monad (filterM, liftM)
+import System.Directory (getDirectoryContents)
hunk ./PowerMate.hsc 36
-getName :: FilePath -> IO String
-getName filename = do
+getUSBName :: FilePath -> IO String
+getUSBName filename = do
hunk ./PowerMate.hsc 39
+
+searchForDevice :: IO (Maybe FilePath)
+searchForDevice = do
+  files <- getDirectoryContents basedir
+  let goodfiles = filter ("event" `isPrefixOf`) files
+  let paths = [basedir ++ "/" ++ file | file <- goodfiles]
+  -- There's this: find :: (a -> Bool) -> [a] -> Maybe a
+  -- but I want: (a -> m Bool) -> [a] -> m (Maybe a)
+  inputs <- filterM deviceIsGood paths
+  return $ case inputs of
+    []    -> Nothing
+    (x:_) -> Just x
+  where basedir = "/dev/input"
+        deviceIsGood path = do
+          putStr (path ++ ": ")
+          hFlush stdout
+          name <- getUSBName path
+          putStrLn name
+          return $ nameIsGood name
+        nameIsGood "Griffin PowerMate" = True
+        nameIsGood _                   = False
}