Docx Reader: Get rid of Modifiable typeclass.

The docx reader used to use a Modifiable typeclass to combine both
Blocks and Inlines. But all the work was in the inlines. So most of the
generality was wasted, at the expense of making the code harder to
understand. This gets rid of the generality, and adds functions for
Blocks and Inlines. It should be a bit easier to work with going forward.

1 files changed, 154 insertions, 0 deletions

diff --git a/src/Text/Pandoc/Readers/Docx/Combine.hs b/src/Text/Pandoc/Readers/Docx/Combine.hs
new file mode 100644
index 000000000..39e0df825
--- /dev/null
+++ b/src/Text/Pandoc/Readers/Docx/Combine.hs
@@ -0,0 +1,154 @@
+{-# LANGUAGE TypeSynonymInstances, FlexibleInstances,
+    PatternGuards #-}
+
+module Text.Pandoc.Readers.Docx.Combine ( smushInlines
+                                        , smushBlocks
+                                        )
+       where
+
+import Text.Pandoc.Builder
+import Data.List
+import Data.Sequence (ViewR(..), ViewL(..), viewl, viewr, (><), (|>))
+import qualified Data.Sequence as Seq (null)
+
+data Modifier a = Modifier (a -> a)
+                | AttrModifier (Attr -> a -> a) Attr
+                | NullModifier
+
+spaceOutInlinesL :: Inlines -> (Inlines, Inlines)
+spaceOutInlinesL ms = (l, stackInlines fs (m' <> r))
+  where (l, m, r) = spaceOutInlines ms
+        (fs, m')  = unstackInlines m
+
+spaceOutInlinesR :: Inlines -> (Inlines, Inlines)
+spaceOutInlinesR ms = (stackInlines fs (l <> m'), r)
+  where (l, m, r) = spaceOutInlines ms
+        (fs, m')  = unstackInlines m
+
+spaceOutInlines :: Inlines -> (Inlines, Inlines, Inlines)
+spaceOutInlines ils =
+  let (fs, ils') = unstackInlines ils
+      contents = unMany ils'
+      left  = case viewl contents of
+        (Space :< _) -> space
+        _            -> mempty
+      right = case viewr contents of
+        (_ :> Space) -> space
+        _            -> mempty in
+  (left, (stackInlines fs $ trimInlines . Many $ contents), right)
+
+stackInlines :: [Modifier Inlines] -> Inlines -> Inlines
+stackInlines [] ms = ms
+stackInlines (NullModifier : fs) ms = stackInlines fs ms
+stackInlines ((Modifier f) : fs) ms =
+  if isEmpty ms
+  then stackInlines fs ms
+  else f $ stackInlines fs ms
+stackInlines ((AttrModifier f attr) : fs) ms = f attr $ stackInlines fs ms
+
+unstackInlines :: Inlines -> ([Modifier Inlines], Inlines)
+unstackInlines ms = case ilModifier ms of
+  NullModifier -> ([], ms)
+  _            -> (f : fs, ms') where
+    f = ilModifier ms
+    (fs, ms') = unstackInlines $ ilInnards ms
+
+ilModifier :: Inlines -> Modifier Inlines
+ilModifier ils = case viewl (unMany ils) of
+  (x :< xs) | Seq.null xs -> case x of
+    (Emph _)        -> Modifier emph
+    (Strong _)      -> Modifier strong
+    (SmallCaps _)   -> Modifier smallcaps
+    (Strikeout _)   -> Modifier strikeout
+    (Superscript _) -> Modifier superscript
+    (Subscript _)   -> Modifier subscript
+    (Link attr _ tgt) -> Modifier $ linkWith attr (fst tgt) (snd tgt)
+    (Span attr _)   -> AttrModifier spanWith attr
+    _               -> NullModifier
+  _ -> NullModifier
+
+ilInnards :: Inlines -> Inlines
+ilInnards ils = case viewl (unMany ils) of
+  (x :< xs) | Seq.null xs -> case x of
+    (Emph lst)        -> fromList lst
+    (Strong lst)      -> fromList lst
+    (SmallCaps lst)   -> fromList lst
+    (Strikeout lst)   -> fromList lst
+    (Superscript lst) -> fromList lst
+    (Subscript lst)   -> fromList lst
+    (Link _ lst _)    -> fromList lst
+    (Span _ lst)      -> fromList lst
+    _        -> ils
+  _          -> ils
+
+inlinesL :: Inlines -> (Inlines, Inlines)
+inlinesL ils = case viewl $ unMany ils of
+  (s :< sq) -> (singleton s, Many sq)
+  _          -> (mempty, ils)
+
+inlinesR :: Inlines -> (Inlines, Inlines)
+inlinesR ils = case viewr $ unMany ils of
+  (sq :> s) -> (Many sq, singleton s)
+  _          -> (ils, mempty)
+
+combineInlines :: Inlines -> Inlines -> Inlines
+combineInlines x y =
+  let (xs', x') = inlinesR x
+      (y', ys') = inlinesL y
+  in
+   xs' <> (combineSingletonInlines x' y') <> ys'
+
+combineSingletonInlines :: Inlines -> Inlines -> Inlines
+combineSingletonInlines x y =
+  let (xfs, xs) = unstackInlines x
+      (yfs, ys) = unstackInlines y
+      shared = xfs `intersect` yfs
+      x_remaining = xfs \\ shared
+      y_remaining = yfs \\ shared
+      x_rem_attr = filter isAttrModifier x_remaining
+      y_rem_attr = filter isAttrModifier y_remaining
+  in
+   case null shared of
+     True | isEmpty xs && isEmpty ys ->
+            stackInlines (x_rem_attr ++ y_rem_attr) mempty
+          | isEmpty xs ->
+            let (sp, y') = spaceOutInlinesL y in
+            (stackInlines x_rem_attr mempty) <> sp <> y'
+          | isEmpty ys ->
+            let (x', sp) = spaceOutInlinesR x in
+            x' <> sp <> (stackInlines y_rem_attr mempty)
+          | otherwise ->
+              let (x', xsp) = spaceOutInlinesR x
+                  (ysp, y') = spaceOutInlinesL y
+              in
+               x' <> xsp <> ysp <> y'
+     False -> stackInlines shared $
+              combineInlines
+              (stackInlines x_remaining xs)
+              (stackInlines y_remaining ys)
+
+combineBlocks :: Blocks -> Blocks -> Blocks
+combineBlocks bs cs
+  | bs' :> (BlockQuote bs'') <- viewr (unMany bs)
+  , (BlockQuote cs'') :< cs' <- viewl (unMany cs) =
+      Many $ (bs' |> (BlockQuote (bs'' <> cs''))) >< cs'
+combineBlocks bs cs = bs <> cs
+
+instance (Monoid a, Eq a) => Eq (Modifier a) where
+  (Modifier f) == (Modifier g) = (f mempty == g mempty)
+  (AttrModifier f attr) == (AttrModifier g attr') = (f attr mempty == g attr' mempty)
+  (NullModifier) == (NullModifier) = True
+  _ == _ = False
+
+isEmpty :: (Monoid a, Eq a) => a -> Bool
+isEmpty x = x == mempty
+
+isAttrModifier :: Modifier a -> Bool
+isAttrModifier (AttrModifier _ _) = True
+isAttrModifier _                  = False
+
+smushInlines :: [Inlines] -> Inlines
+smushInlines xs = foldl combineInlines mempty xs
+
+smushBlocks :: [Blocks] -> Blocks
+smushBlocks xs = foldl combineBlocks mempty xs