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1 files changed, 79 insertions, 0 deletions

diff --git a/Presence/Nesting.hs b/Presence/Nesting.hs
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+++ b/Presence/Nesting.hs
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+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE FlexibleContexts #-}
+module Nesting where
+
+import Data.Conduit
+import Data.Conduit.Lift
+import Data.XML.Types
+import qualified Data.Text as S
+import Control.Monad.State
+import qualified Data.List as List
+
+type Lang = S.Text
+
+data StrictList a = a :! !(StrictList a) | StrictNil
+
+data XMLState = XMLState { 
+        nestingLevel :: Int,
+        langStack :: StrictList (Int,Lang)
+}
+
+type NestingXML o m a = ConduitM Event o (StateT XMLState m) a
+
+doNestingXML :: Monad m => NestingXML o m r -> ConduitM Event o m r
+doNestingXML m = 
+    evalStateC (XMLState 0 StrictNil) (trackNesting =$= m)
+
+nesting :: Monad m => NestingXML o m Int
+nesting = lift $ (return . nestingLevel) =<< get
+
+
+trackNesting :: Monad m => ConduitM Event Event (StateT XMLState m) ()
+trackNesting = awaitForever doit
+ where
+  doit xml = do
+    XMLState lvl langs <- lift get
+    lift . put $ case xml of
+              EventBeginElement _ attrs -> 
+                case lookupLang attrs of
+                  Nothing   -> XMLState (lvl+1) langs
+                  Just lang -> XMLState (lvl+1) ( (lvl+1,lang) :! langs)
+              EventEndElement _     -> 
+                case langs of 
+                  (llvl,_) :! ls | llvl==lvl -> XMLState (lvl-1) ls
+                  _              | otherwise -> XMLState (lvl-1) langs
+              _  -> XMLState lvl langs
+    yield xml
+
+
+lookupLang attrs =
+    case List.find ( (=="xml:lang") . fst) attrs of
+        Just (_,[ContentText x])   -> Just x
+        Just (_,[ContentEntity x]) -> Just x
+        _                          -> Nothing
+
+
+awaitCloser :: Monad m => Int -> NestingXML o m ()
+awaitCloser lvl = do
+    fix $ \loop -> do
+        lvl' <- nesting
+        when (lvl' >= lvl) $ do
+        xml <- await
+        maybe (return ()) (const loop) xml
+
+withXML f = await >>= maybe (return ()) f
+
+nextElement :: Monad m => NestingXML o m (Maybe Event)
+nextElement = do
+    lvl <- nesting
+    fix $ \loop  -> do
+        xml <- await
+        case xml of
+            Nothing                      -> return Nothing
+            Just (EventBeginElement _ _) -> do
+                return xml
+            Just _ -> do
+                lvl' <- nesting
+                if (lvl'>=lvl) then loop 
+                               else return Nothing
+