docbook2txt: halfway finish <informaltable>

This required a lot of restructuring, which is why I won't
put this on another branch.

A part of the library which is updated in github but not yet at hackage,
is needed to continue. Specifically, the `Monoid` instance in
`Text.Layout.Table.Cell.Formatted` is needed to put together multiple
colored text in a table.

Among other things introduced, there is now our own `Formatted` type
which is used to await formatting until things like tables come up.
Compared to the earlier `IO ()` approach, this is probably a lot better.

internals/docbook2txt/default.nix

@@ -1,4 +1,4 @@
 { pkgs, compiler ? "ghc924", ... }:
 pkgs.writers.writeHaskellBin "docbook2txt" {
-  libraries = with pkgs.haskellPackages; [ tagsoup ansi-terminal split text ];
+  libraries = with pkgs.haskellPackages; [ tagsoup ansi-terminal split table-layout text ];
 } (builtins.readFile ./docbook2txt.hs)

internals/docbook2txt/docbook2txt.hs

@@ -8,16 +8,93 @@
 --   end up having to write custom conversion logic for every tag to be
 --   consumed by pandoc anyway. So instead, I am just planning on keeping
 --   my own module parsing raw xml tags (for now).
-
+{-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE PatternSynonyms #-}
 
+import Data.Char (isSpace)
 import Data.List (find, intersperse)
 import Data.List.Split (splitOn)
-import qualified System.Console.ANSI as AN
+import Data.Maybe (fromMaybe)
+import Data.String (IsString, fromString)
+import qualified System.Console.ANSI.Codes as AN
 import qualified System.Console.ANSI.Types as AN
 import System.Environment (getArgs)
 import qualified Text.HTML.TagSoup as TS
 import qualified Text.HTML.TagSoup.Tree as TS
+-- import qualified Text.Layout.Table as T
+-- import qualified Text.Layout.Table.Cell as T
+-- import qualified Text.Layout.Table.Cell.Formatted as T
+
+--
+-- Datatypes with relevant methods
+--
+
+-- TODO: Mark reflowable text, and do a reflow fold before print.
+
+-- data ShouldReflow a = SRReflow a
+--                     | SRConstant a
+--   deriving (Show, Eq)
+
+data Formatted
+  = FSeveral [Formatted]
+  | FWrapped String Formatted String
+  | FPlain String
+  deriving (Eq)
+
+instance IsString Formatted where
+  fromString = FPlain
+
+instance Show Formatted where
+  show (FSeveral fs) = concatMap show fs
+  show (FWrapped w1 s w2) = concat [w1, show s, w2]
+  show (FPlain s) = s
+
+instance Semigroup Formatted where
+  FSeveral x <> FSeveral y = FSeveral $ x ++ y
+  f1 <> FSeveral x = FSeveral $ f1 : x
+  FSeveral x <> f1 = FSeveral $ x ++ [f1]
+  f1 <> f2 = FSeveral [f1, f2]
+
+instance Monoid Formatted where
+  mempty = FPlain mempty
+
+realString :: Formatted -> String
+realString (FSeveral fs) = concatMap realString fs
+realString (FWrapped w1 s w2) = realString s
+realString (FPlain s) = s
+
+realLength :: Formatted -> Int
+realLength = length . realString
+
+-- TODO: Revisit when table-layout gets a new release
+-- https://github.com/muesli4/table-layout/issues/43
+
+-- toTableFormattedType :: Formatted -> T.Formatted String
+-- toTableFormattedType f = case f of
+--   FSeveral fs -> mconcatMap toTableFormattedType fs
+--   FWrapped w1 (FPlain s) w2 -> T.formatted w1 s w2
+--   FWrapped _ f1 _ -> toTableFormattedType f1
+--   FPlain s -> T.plain s
+
+data PotentiallyColorizedString = PCS
+  { colorized :: Formatted,
+    nonColorized :: String
+  }
+  deriving (Show, Eq)
+
+instance Semigroup PotentiallyColorizedString where
+  pcs1 <> pcs2 =
+    PCS
+      { colorized = colorized pcs1 <> colorized pcs2,
+        nonColorized = nonColorized pcs1 <> nonColorized pcs2
+      }
+
+instance Monoid PotentiallyColorizedString where
+  mempty =
+    PCS
+      { colorized = mempty,
+        nonColorized = mempty
+      }
 
 main :: IO ()
 main = do
@@ -26,10 +103,32 @@ main = do
   let colorizedMode = "-C" `elem` args
   printTags colorizedMode $ map replaceTagColor $ removeParagraphTags $ TS.parseTree stdin
 
-data PotentiallyColorizedString = PCS
-  { colorized :: IO (),
-    nonColorized :: String
-  }
+-- Print a list of PCSs.
+-- Depending on the first argument, the color can be optionally
+-- colored.
+printTags :: Bool -> [PotentiallyColorizedString] -> IO ()
+printTags False = putStrLn . unwords . map nonColorized
+printTags True = putStrLn . mconcatMap (show . colorized)
+
+-- ANSI helpers
+
+wrapSGR :: AN.SGR -> String -> Formatted
+wrapSGR sgr str = FWrapped (AN.setSGRCode [sgr]) (fromString str) (AN.setSGRCode [AN.Reset])
+
+wrapColor :: AN.Color -> String -> Formatted
+wrapColor = wrapSGR . AN.SetColor AN.Foreground AN.Vivid
+
+wrapTxt :: String -> String -> String
+wrapTxt delimiter string = concat [delimiter, string, delimiter]
+
+wrapTxt' :: String -> Formatted -> Formatted
+wrapTxt' delimiter string = FSeveral [fromString delimiter, string, fromString delimiter]
+
+bold :: AN.SGR
+bold = AN.SetConsoleIntensity AN.BoldIntensity
+
+mconcatMap :: Monoid b => (a -> b) -> [a] -> b
+mconcatMap f = mconcat . map f
 
 -- Remove `</para><para>` tags.
 -- If there are more in one doc comment, the middle ones
@@ -45,30 +144,6 @@ removeParagraphTags (TS.TagLeaf (TS.TagOpen "para" _) : rest) = removeParagraphT
 removeParagraphTags (x : y : rest) = x : removeParagraphTags (y : rest)
 removeParagraphTags x = x
 
--- Print a list of PCSs.
--- Depending on the first argument, the color can be optionally
--- colored.
-printTags :: Bool -> [PotentiallyColorizedString] -> IO ()
-printTags False = putStrLn . unwords . map nonColorized
-printTags True = mapM_ colorized
-
--- ANSI helpers
-
-wrapSGR :: AN.SGR -> String -> IO ()
-wrapSGR sgr str = do
-  AN.setSGR [sgr]
-  putStr str
-  AN.setSGR [AN.Reset]
-
-wrapColor :: AN.Color -> String -> IO ()
-wrapColor c = wrapSGR (AN.SetColor AN.Foreground AN.Vivid c)
-
-wrapTxt :: String -> String -> String
-wrapTxt delimiter string = concat [delimiter, string, delimiter]
-
-bold :: AN.SGR
-bold = AN.SetConsoleIntensity AN.BoldIntensity
-
 pattern TextLeaf a = TS.TagLeaf (TS.TagText a)
 
 -- Replace tags with their PCS string equivalent.
@@ -76,12 +151,12 @@ replaceTagColor :: TS.TagTree String -> PotentiallyColorizedString
 replaceTagColor tagtree = case tagtree of
   TS.TagLeaf (TS.TagText s) ->
     PCS
-      { colorized = putStr s,
+      { colorized = fromString s,
         nonColorized = s
       }
   TS.TagBranch "para" _ inner ->
     PCS
-      { colorized = mapM_ (colorized . replaceTagColor) inner,
+      { colorized = mconcatMap (colorized . replaceTagColor) inner,
         nonColorized = concatMap (nonColorized . replaceTagColor) inner
       }
   TS.TagBranch "code" _ [TextLeaf content] ->
@@ -136,12 +211,12 @@ replaceTagColor tagtree = case tagtree of
       }
   TS.TagBranch "quote" _ inner ->
     PCS
-      { colorized = sequence_ [putStr "\"", mapM_ (colorized . replaceTagColor) inner, putStr "\""],
+      { colorized = wrapTxt' "\"" $ mconcatMap (colorized . replaceTagColor) inner,
         nonColorized = wrapTxt "\"" $ concatMap (nonColorized . replaceTagColor) inner
       }
   TS.TagBranch "warning" _ inner ->
     PCS
-      { colorized = sequence_ [wrapColor AN.Red "WARNING: ", mapM_ (colorized . replaceTagColor) inner],
+      { colorized = mconcat [wrapColor AN.Red "WARNING: ", mconcatMap (colorized . replaceTagColor) inner],
         nonColorized = "WARNING: " ++ concatMap (nonColorized . replaceTagColor) inner
       }
   TS.TagBranch "xref" [("linkend", link)] [] ->
@@ -149,15 +224,57 @@ replaceTagColor tagtree = case tagtree of
         removeOptPrefix ('o' : 'p' : 't' : '-' : rest) = rest
         removeOptPrefix x = x
 
-        replaceName :: String -> IO ()
-        replaceName x = if x == "_name_" then wrapColor AN.Red "<name>" else wrapSGR bold x
+        replaceName :: String -> Formatted
+        replaceName "_name_" = wrapColor AN.Red "<name>"
+        replaceName x = wrapSGR bold x
 
-        formattedLink :: [IO ()]
-        formattedLink = intersperse (wrapSGR bold ".") $ map replaceName $ splitOn "." $ removeOptPrefix link
+        formattedLink :: Formatted
+        formattedLink = mconcat $ intersperse (wrapSGR bold ".") $ map replaceName $ splitOn "." $ removeOptPrefix link
      in PCS
-          { colorized = sequence_ $ [putStr "`"] ++ formattedLink ++ [putStr "`"],
+          { colorized = wrapTxt' "`" formattedLink,
             nonColorized = wrapTxt "`" link
           }
+  -- TS.TagBranch "informaltable" _ [inner] ->
+  --   let
+  --     extractRows :: TS.TagTree String -> Maybe [TS.TagTree String]
+  --     extractRows (TS.TagBranch "tgroup" _ [TS.TagBranch "tbody" _ rows]) = Just rows
+  --     extractRows _ = Nothing
+
+  --     -- TODO: This filters too much
+  --     isWhiteSpace :: TS.TagTree String -> Bool
+  --     isWhiteSpace (TextLeaf s) = False
+  --     isWhiteSpace _ = True
+
+  --     parseRow :: TS.TagTree String -> Maybe [PotentiallyColorizedString]
+  --     parseRow (TS.TagBranch "row" _ entries) = sequence $ map parseEntry $ filter isWhiteSpace entries
+  --     parseRow _ = Nothing
+
+  --     parseEntry :: TS.TagTree String -> Maybe PotentiallyColorizedString
+  --     parseEntry (TS.TagBranch "entry" _ content) = Just $ mconcatMap replaceTagColor content
+  --     parseEntry _ = Nothing
+
+  --     rawRows :: Maybe [[PotentiallyColorizedString]]
+  --     rawRows = do
+  --       rows <- extractRows inner
+  --       sequence $ map parseRow $ filter isWhiteSpace rows
+
+  --     generateColSpec :: [[a]] -> [T.ColSpec]
+  --     generateColSpec rs = flip replicate T.def $ length $ rs !! 0
+
+  --     generateTableConfig :: T.Cell a => [[b]] -> [T.RowGroup a] -> String
+  --     generateTableConfig rs = (++) "\n" . T.tableString (generateColSpec rs) T.unicodeRoundS T.def
+
+  --     table :: T.Cell a => (PotentiallyColorizedString -> a) -> Maybe String
+  --     table f = case rawRows of
+  --       Nothing -> Nothing
+  --       Just rrs -> Just $ generateTableConfig rrs $ map (T.rowG . map f) $ rrs
+
+  --     errorMessage :: String
+  --     errorMessage = "ERROR: Could not parse <informaltable>";
+  --   in PCS {
+  --     colorized = fromMaybe (wrapColor AN.Red errorMessage) (FPlain <$> table (toTableFormattedType . colorized)),
+  --     nonColorized = fromMaybe errorMessage $ table nonColorized
+  --   }
   TS.TagBranch "citerefentry" _ content ->
     let tagBranchTagMatches :: String -> TS.TagTree String -> Bool
         tagBranchTagMatches x (TS.TagBranch tag _ _) = tag == x