content: {-# LANGUAGE CPP                   #-}
  {-# LANGUAGE FlexibleContexts      #-}
  {-# LANGUAGE MultiParamTypeClasses #-}
  {-# LANGUAGE ScopedTypeVariables   #-}
  {-# LANGUAGE ViewPatterns          #-}
  {-# LANGUAGE FlexibleInstances     #-}
  {-# LANGUAGE LambdaCase            #-}
  {-# LANGUAGE OverloadedStrings     #-}
  {- |
     Module      : Text.Pandoc.Shared
     Copyright   : Copyright (C) 2006-2024 John MacFarlane
     License     : GNU GPL, version 2 or above
  
     Maintainer  : John MacFarlane <jgm@berkeley.edu>
     Stability   : alpha
     Portability : portable
  
  Utility functions and definitions used by the various Pandoc modules.
  -}
  module Text.Pandoc.Shared (
                       -- * List processing
                       splitBy,
                       splitTextBy,
                       splitTextByIndices,
                       -- * Text processing
                       inquotes,
                       tshow,
                       stripTrailingNewlines,
                       trim,
                       triml,
                       trimr,
                       trimMath,
                       stripFirstAndLast,
                       camelCaseToHyphenated,
                       camelCaseStrToHyphenated,
                       toRomanNumeral,
                       tabFilter,
                       -- * Date/time
                       normalizeDate,
                       -- * Pandoc block and inline list processing
                       addPandocAttributes,
                       orderedListMarkers,
                       extractSpaces,
                       removeFormatting,
                       deNote,
                       stringify,
                       capitalize,
                       compactify,
                       compactifyDL,
                       linesToPara,
                       figureDiv,
                       makeSections,
                       makeSectionsWithOffsets,
                       combineAttr,
                       uniqueIdent,
                       inlineListToIdentifier,
                       textToIdentifier,
                       isHeaderBlock,
                       onlySimpleTableCells,
                       isTightList,
                       taskListItemFromAscii,
                       taskListItemToAscii,
                       handleTaskListItem,
                       addMetaField,
                       htmlSpanLikeElements,
                       formatCode,
                       -- * TagSoup HTML handling
                       renderTags',
                       -- * File handling
                       inDirectory,
                       makeCanonical,
                       collapseFilePath,
                       filteredFilesFromArchive,
                       -- * for squashing blocks
                       blocksToInlines,
                       blocksToInlines',
                       blocksToInlinesWithSep,
                       defaultBlocksSeparator,
                       -- * Safe read
                       safeRead,
                       safeStrRead
                      ) where
  
  import Codec.Archive.Zip
  import qualified Control.Exception as E
  import Control.Monad (MonadPlus (..), msum, unless)
  import qualified Control.Monad.State.Strict as S
  import qualified Data.ByteString.Lazy as BL
  import Data.Containers.ListUtils (nubOrd)
  import Data.Char (isAlpha, isLower, isSpace, isUpper, toLower, isAlphaNum,
                    generalCategory, GeneralCategory(NonSpacingMark,
                    SpacingCombiningMark, EnclosingMark, ConnectorPunctuation))
  import Data.List (find, foldl', groupBy, intercalate, intersperse, union)
  import qualified Data.Map as M
  import Data.Maybe (mapMaybe)
  import Data.Monoid (Any (..) )
  import Data.Semigroup (Min (..))
  import Data.Sequence (ViewL (..), ViewR (..), viewl, viewr)
  import qualified Data.Set as Set
  import qualified Data.Text as T
  import qualified Text.Emoji as Emoji
  import System.Directory
  import System.FilePath (isPathSeparator, splitDirectories)
  import qualified System.FilePath.Posix as Posix
  import Text.HTML.TagSoup (RenderOptions (..), Tag (..), renderOptions,
                            renderTagsOptions)
  import Text.Pandoc.Builder (Blocks, Inlines, ToMetaValue (..))
  import qualified Text.Pandoc.Builder as B
  import Data.Time
  import Text.Pandoc.Asciify (toAsciiText)
  import Text.Pandoc.Definition
  import Text.Pandoc.Extensions (Extensions, Extension(..), extensionEnabled)
  import Text.DocLayout (charWidth)
  import Text.Pandoc.Walk
  -- for addPandocAttributes:
  import Commonmark.Pandoc (Cm(..))
  import Commonmark (HasAttributes(..))
  
  --
  -- List processing
  --
  
  -- | Split list by groups of one or more sep.
  splitBy :: (a -> Bool) -> [a] -> [[a]]
  splitBy _ [] = []
  splitBy isSep lst =
    let (first, rest) = break isSep lst
    in  first:splitBy isSep (dropWhile isSep rest)
  
  -- | Split text by groups of one or more separator.
  splitTextBy :: (Char -> Bool) -> T.Text -> [T.Text]
  splitTextBy isSep t
    | T.null t = []
    | otherwise = let (first, rest) = T.break isSep t
                  in  first : splitTextBy isSep (T.dropWhile isSep rest)
  
  -- | Split text at the given widths. Note that the break points are
  -- /not/ indices but text widths, which will be different for East Asian
  -- characters, emojis, etc.
  splitTextByIndices :: [Int] -> T.Text -> [T.Text]
  splitTextByIndices ns = splitTextByRelIndices (zipWith (-) ns (0:ns)) . T.unpack
   where
    splitTextByRelIndices [] cs = [T.pack cs]
    splitTextByRelIndices (x:xs) cs =
      let (first, rest) = splitAt' x cs
       in T.pack first : splitTextByRelIndices xs rest
  
  -- | Returns a pair whose first element is a prefix of @t@ and that has
  -- width @n@, and whose second is the remainder of the string.
  --
  -- Note: Do *not* replace this with 'T.splitAt', which is not sensitive
  -- to character widths!
  splitAt' :: Int {-^ n -} -> [Char] {-^ t -} -> ([Char],[Char])
  splitAt' _ []          = ([],[])
  splitAt' n xs | n <= 0 = ([],xs)
  splitAt' n (x:xs)      = (x:ys,zs)
    where (ys,zs) = splitAt' (n - charWidth x) xs
  
  --
  -- Text processing
  --
  
  -- | Wrap double quotes around a Text
  inquotes :: T.Text -> T.Text
  inquotes txt = T.cons '\"' (T.snoc txt '\"')
  
  -- | Like @'show'@, but returns a 'T.Text' instead of a 'String'.
  tshow :: Show a => a -> T.Text
  tshow = T.pack . show
  
  -- | Strip trailing newlines from string.
  stripTrailingNewlines :: T.Text -> T.Text
  stripTrailingNewlines = T.dropWhileEnd (== '\n')
  
  -- | Returns 'True' for an ASCII whitespace character, viz. space,
  -- carriage return, newline, and horizontal tab.
  isWS :: Char -> Bool
  isWS ' '  = True
  isWS '\r' = True
  isWS '\n' = True
  isWS '\t' = True
  isWS _    = False
  
  -- | Remove leading and trailing space (including newlines) from string.
  trim :: T.Text -> T.Text
  trim = T.dropAround isWS
  
  -- | Remove leading space (including newlines) from string.
  triml :: T.Text -> T.Text
  triml = T.dropWhile isWS
  
  -- | Remove trailing space (including newlines) from string.
  trimr :: T.Text -> T.Text
  trimr = T.dropWhileEnd isWS
  
  -- | Trim leading space and trailing space unless after \.
  trimMath :: T.Text -> T.Text
  trimMath = triml . T.reverse . stripBeginSpace . T.reverse -- no Text.spanEnd
    where
      stripBeginSpace t
        | T.null pref = t
        | Just ('\\', _) <- T.uncons suff = T.cons (T.last pref) suff
        | otherwise = suff
        where
          (pref, suff) = T.span isWS t
  
  -- | Strip leading and trailing characters from string
  stripFirstAndLast :: T.Text -> T.Text
  stripFirstAndLast t = case T.uncons t of
    Just (_, t') -> case T.unsnoc t' of
      Just (t'', _) -> t''
      _             -> t'
    _               -> ""
  
  -- | Change CamelCase word to hyphenated lowercase (e.g., camel-case).
  camelCaseToHyphenated :: T.Text -> T.Text
  camelCaseToHyphenated = T.pack . camelCaseStrToHyphenated . T.unpack
  
  -- This may not work as expected on general Unicode, if it contains
  -- letters with a longer lower case form than upper case. I don't know
  -- what the camel case practices of affected scripts are, though.
  camelCaseStrToHyphenated :: String -> String
  camelCaseStrToHyphenated [] = ""
  camelCaseStrToHyphenated (a:b:rest)
    | isLower a
    , isUpper b = a:'-':toLower b:camelCaseStrToHyphenated rest
  -- handle ABCDef = abc-def
  camelCaseStrToHyphenated (a:b:c:rest)
    | isUpper a
    , isUpper b
    , isLower c = toLower a:'-':toLower b:camelCaseStrToHyphenated (c:rest)
  camelCaseStrToHyphenated (a:rest) = toLower a:camelCaseStrToHyphenated rest
  
  -- | Convert number < 4000 to uppercase roman numeral.
  toRomanNumeral :: Int -> T.Text
  toRomanNumeral x
    | x >= 4000 || x < 0 = "?"
    | x >= 1000 = "M" <> toRomanNumeral (x - 1000)
    | x >= 900  = "CM" <> toRomanNumeral (x - 900)
    | x >= 500  = "D" <> toRomanNumeral (x - 500)
    | x >= 400  = "CD" <> toRomanNumeral (x - 400)
    | x >= 100  = "C" <> toRomanNumeral (x - 100)
    | x >= 90   = "XC" <> toRomanNumeral (x - 90)
    | x >= 50   = "L"  <> toRomanNumeral (x - 50)
    | x >= 40   = "XL" <> toRomanNumeral (x - 40)
    | x >= 10   = "X" <> toRomanNumeral (x - 10)
    | x == 9    = "IX"
    | x >= 5    = "V" <> toRomanNumeral (x - 5)
    | x == 4    = "IV"
    | x >= 1    = "I" <> toRomanNumeral (x - 1)
    | otherwise = ""
  
  -- | Convert tabs to spaces. Tabs will be preserved if tab stop is set to 0.
  tabFilter :: Int       -- ^ Tab stop
            -> T.Text    -- ^ Input
            -> T.Text
  tabFilter 0 = id
  tabFilter tabStop = T.unlines . map go . T.lines
    where go s =
           let (s1, s2) = T.break (== '\t') s
           in  if T.null s2
                  then s1
                  else s1 <> T.replicate
                         (tabStop - (T.length s1 `mod` tabStop)) (T.pack " ")
                         <> go (T.drop 1 s2)
  
  --
  -- Date/time
  --
  
  -- | Parse a date and convert (if possible) to "YYYY-MM-DD" format. We
  -- limit years to the range 1601-9999 (ISO 8601 accepts greater than
  -- or equal to 1583, but MS Word only accepts dates starting 1601).
  normalizeDate :: T.Text -> Maybe T.Text
  normalizeDate = fmap T.pack . normalizeDate' . T.unpack
  
  -- | Like @'normalizeDate'@, but acts on 'String' instead of 'T.Text'.
  normalizeDate' :: String -> Maybe String
  normalizeDate' s = fmap (formatTime defaultTimeLocale "%F")
    (msum $ map (\fs -> parsetimeWith fs s >>= rejectBadYear) formats :: Maybe Day)
    where rejectBadYear day = case toGregorian day of
            (y, _, _) | y >= 1601 && y <= 9999 -> Just day
            _         -> Nothing
          parsetimeWith = parseTimeM True defaultTimeLocale
          formats = ["%x","%m/%d/%Y", "%D","%F", "%d %b %Y",
                      "%e %B %Y", "%b. %e, %Y", "%B %e, %Y",
                      "%Y%m%d", "%Y%m", "%Y"]
  
  --
  -- Pandoc block and inline list processing
  --
  
  -- | Add key-value attributes to a pandoc element. If the element
  -- does not have a slot for attributes, create an enclosing Span
  -- (for Inlines) or Div (for Blocks).  Note that both 'Cm () Inlines'
  -- and 'Cm () Blocks' are instances of 'HasAttributes'.
  addPandocAttributes
    :: forall b . HasAttributes (Cm () b) => [(T.Text, T.Text)] -> b -> b
  addPandocAttributes [] bs = bs
  addPandocAttributes kvs bs =
    unCm . addAttributes kvs $ (Cm bs :: Cm () b)
  
  -- | Generate infinite lazy list of markers for an ordered list,
  -- depending on list attributes.
  orderedListMarkers :: (Int, ListNumberStyle, ListNumberDelim) -> [T.Text]
  orderedListMarkers (start, numstyle, numdelim) =
    let nums = case numstyle of
                       DefaultStyle -> map tshow [start..]
                       Example      -> map tshow [start..]
                       Decimal      -> map tshow [start..]
                       UpperAlpha   -> drop (start - 1) $ cycle $
                                       map T.singleton ['A'..'Z']
                       LowerAlpha   -> drop (start - 1) $ cycle $
                                       map T.singleton ['a'..'z']
                       UpperRoman   -> map toRomanNumeral [start..]
                       LowerRoman   -> map (T.toLower . toRomanNumeral) [start..]
        inDelim str = case numdelim of
                              DefaultDelim -> str <> "."
                              Period       -> str <> "."
                              OneParen     -> str <> ")"
                              TwoParens    -> "(" <> str <> ")"
    in  map inDelim nums
  
  
  -- | Extract the leading and trailing spaces from inside an inline element
  -- and place them outside the element.  SoftBreaks count as Spaces for
  -- these purposes.
  extractSpaces :: (Inlines -> Inlines) -> Inlines -> Inlines
  extractSpaces f is =
    let contents = B.unMany is
        left  = case viewl contents of
                      (Space :< _)     -> B.space
                      (SoftBreak :< _) -> B.softbreak
                      _                -> mempty
        right = case viewr contents of
                      (_ :> Space)     -> B.space
                      (_ :> SoftBreak) -> B.softbreak
                      _                -> mempty in
    (left <> f (B.trimInlines . B.Many $ contents) <> right)
  
  -- | Extract inlines, removing formatting.
  removeFormatting :: Walkable Inline a => a -> [Inline]
  removeFormatting = query go . walk (deNote . deQuote)
    where go :: Inline -> [Inline]
          go (Str xs)   = [Str xs]
          go Space      = [Space]
          go SoftBreak  = [SoftBreak]
          go (Code _ x) = [Str x]
          go (Math _ x) = [Str x]
          go LineBreak  = [Space]
          go _          = []
  
  -- | Replaces 'Note' elements with empty strings.
  deNote :: Inline -> Inline
  deNote (Note _) = Str ""
  deNote x        = x
  
  -- | Convert pandoc structure to a string with formatting removed.
  -- Footnotes are skipped (since we don't want their contents in link
  -- labels).
  stringify :: Walkable Inline a => a -> T.Text
  stringify = query go . walk fixInlines
    where go :: Inline -> T.Text
          go Space                                       = " "
          go SoftBreak                                   = " "
          go (Str x)                                     = x
          go (Code _ x)                                  = x
          go (Math _ x)                                  = x
          go (RawInline (Format "html") (T.unpack -> ('<':'b':'r':_)))
                                                         = " " -- see #2105
          go LineBreak                                   = " "
          go _                                           = ""
  
          fixInlines :: Inline -> Inline
          fixInlines (Cite _ ils) = Cite [] ils
          fixInlines (Note _) = Note []
          fixInlines (q@Quoted{}) = deQuote q
          fixInlines x = x
  
  -- | Unwrap 'Quoted' inline elements, enclosing the contents with
  -- English-style Unicode quotes instead.
  deQuote :: Inline -> Inline
  deQuote (Quoted SingleQuote xs) =
    Span ("",[],[]) (Str "\8216" : xs ++ [Str "\8217"])
  deQuote (Quoted DoubleQuote xs) =
    Span ("",[],[]) (Str "\8220" : xs ++ [Str "\8221"])
  deQuote x = x
  
  -- | Bring all regular text in a pandoc structure to uppercase.
  --
  -- This function correctly handles cases where a lowercase character doesn't
  -- match to a single uppercase character – e.g. “Straße” would be converted
  -- to “STRASSE”, not “STRAßE”.
  capitalize :: Walkable Inline a => a -> a
  capitalize = walk go
    where go :: Inline -> Inline
          go (Str s) = Str $ T.toUpper s
          go x       = x
  
  -- | Change final list item from @Para@ to @Plain@ if the list contains
  -- no other @Para@ blocks.  Otherwise (if the list items contain @Para@
  -- blocks besides possibly at the end), turn any @Plain@s into @Para@s (#5285).
  compactify :: [Blocks]  -- ^ List of list items (each a list of blocks)
             -> [Blocks]
  compactify [] = []
  compactify items =
    let (others, final) = (init items, last items)
    in  case reverse (B.toList final) of
             (Para a:xs)
               | null [Para x | Para x <- xs ++ concatMap B.toList others]
               -> others ++ [B.fromList (reverse (Plain a : xs))]
             _ | null [Para x | Para x <- concatMap B.toList items]
               -> items
             _ -> map (fmap plainToPara) items
  
  plainToPara :: Block -> Block
  plainToPara (Plain ils) = Para ils
  plainToPara x = x
  
  
  -- | Like @compactify@, but acts on items of definition lists.
  compactifyDL :: [(Inlines, [Blocks])] -> [(Inlines, [Blocks])]
  compactifyDL items =
    case reverse items of
          ((t,ds):ys) ->
             case reverse (map (reverse . B.toList) ds) of
               ((Para x:xs) : zs) | not (any isPara xs) ->
                    reverse ys ++
                      [(t, reverse (map B.fromList zs) ++
                           [B.fromList (reverse (Plain x:xs))])]
               _     -> items
          _          -> items
  
  
  -- | Combine a list of lines by adding hard linebreaks.
  combineLines :: [[Inline]] -> [Inline]
  combineLines = intercalate [LineBreak]
  
  -- | Convert a list of lines into a paragraph with hard line breaks. This is
  --   useful e.g. for rudimentary support of LineBlock elements in writers.
  linesToPara :: [[Inline]] -> Block
  linesToPara = Para . combineLines
  
  -- | Creates a Div block from figure components. The intended use is in
  -- writers of formats that do not have markup support for figures.
  --
  -- The resulting div is given the class @figure@ and contains the figure
  -- body and the figure caption. The latter is wrapped in a 'Div' of
  -- class @caption@, with the stringified @short-caption@ as attribute.
  figureDiv :: Attr -> Caption -> [Block] -> Block
  figureDiv (ident, classes, kv) (Caption shortcapt longcapt) body =
    let divattr = ( ident
                , ["figure"] `union` classes
                , kv
                )
        captkv = maybe mempty (\s -> [("short-caption", stringify s)]) shortcapt
        capt = [Div ("", ["caption"], captkv) longcapt | not (null longcapt)]
    in Div divattr (body ++ capt)
  
  -- | Returns 'True' iff the given element is a 'Para'.
  isPara :: Block -> Bool
  isPara (Para _) = True
  isPara _        = False
  
  -- | Convert Pandoc inline list to plain text identifier.
  inlineListToIdentifier :: Extensions -> [Inline] -> T.Text
  inlineListToIdentifier exts =
    textToIdentifier exts . stringify . unEmojify
    where
      unEmojify :: [Inline] -> [Inline]
      unEmojify
        | extensionEnabled Ext_gfm_auto_identifiers exts ||
          extensionEnabled Ext_ascii_identifiers exts = walk unEmoji
        | otherwise = id
      unEmoji (Span ("",["emoji"],[("data-emoji",ename)]) _) = Str ename
      unEmoji (Str t) = Str (Emoji.replaceEmojis emojisToAliases t)
      unEmoji x = x
      emojisToAliases t [] = t
      emojisToAliases _ (a:_) = a
  
  -- | Convert string to plain text identifier.
  textToIdentifier :: Extensions -> T.Text -> T.Text
  textToIdentifier exts =
    dropNonLetter . filterAscii . toIdent
    where
      dropNonLetter
        | extensionEnabled Ext_gfm_auto_identifiers exts = id
        | otherwise = T.dropWhile (not . isAlpha)
      filterAscii
        | extensionEnabled Ext_ascii_identifiers exts
          = toAsciiText
        | otherwise = id
      toIdent
        | extensionEnabled Ext_gfm_auto_identifiers exts =
          filterPunct . spaceToDash . T.toLower
        | otherwise = T.intercalate "-" . T.words . filterPunct . T.toLower
      filterPunct = T.filter (\c -> isSpace c || isAlphaNum c || isAllowedPunct c)
      isAllowedPunct c
        | extensionEnabled Ext_gfm_auto_identifiers exts
          = c == '-' || c == '_' ||
            generalCategory c `elem` [NonSpacingMark, SpacingCombiningMark,
                                      EnclosingMark, ConnectorPunctuation]
        | otherwise = c == '_' || c == '-' || c == '.'
      spaceToDash = T.map (\c -> if isSpace c then '-' else c)
  
  
  -- | Put a list of Pandoc blocks into a hierarchical structure:
  -- a list of sections (each a Div with class "section" and first
  -- element a Header).  If the 'numbering' parameter is True, Header
  -- numbers are added via the number attribute on the header.
  -- If the baseLevel parameter is Just n, Header levels are
  -- adjusted so that the lowest header level is n.
  -- (There may still be gaps in header level if the author leaves them.)
  makeSections :: Bool -> Maybe Int -> [Block] -> [Block]
  makeSections = makeSectionsWithOffsets []
  
  -- | Like 'makeSections', but with a parameter for number offsets
  -- (a list of 'Int's, the first of which is added to the level 1
  -- section number, the second to the level 2, and so on).
  makeSectionsWithOffsets :: [Int] -> Bool -> Maybe Int -> [Block] -> [Block]
  makeSectionsWithOffsets numoffsets numbering mbBaseLevel bs =
    S.evalState (go bs) numoffsets
   where
    getLevel (Header level _ _) = Min level
    getLevel _ = Min 99
    minLevel = if all (== 0) numoffsets
                  then getMin $ query getLevel bs
                  else 1 -- see #5071, for backwards compatibility
    go :: [Block] -> S.State [Int] [Block]
    go (Header level (ident,classes,kvs) title':xs) = do
      lastnum <- S.get
      let level' = maybe level (\n -> n + level - minLevel) mbBaseLevel
      let adjustNum lev numComponent
            | lev < level = numComponent
            | lev == level = numComponent + 1
            | otherwise = 0
      let newnum = zipWith adjustNum [minLevel..level]
                      (lastnum ++ repeat 0)
      unless (null newnum || "unnumbered" `elem` classes) $ S.put newnum
      let (sectionContents, rest) = break (headerLtEq level) xs
      sectionContents' <- go sectionContents
      rest' <- go rest
      let kvs' = -- don't touch number if already present
                 case lookup "number" kvs of
                    Nothing | numbering
                            , "unnumbered" `notElem` classes ->
                          ("number", T.intercalate "." (map tshow newnum)) : kvs
                    _ -> kvs
      let divattr = (ident, "section":classes, kvs')
      let isHeadingAttr ("epub:type",_) = False
          isHeadingAttr ("role",v) =
            v `elem` ["tab", "presentation", "none", "treeitem",
                      "menuitem", "button", "heading"]
          isHeadingAttr _ = True
      let hattr = ("",classes, filter isHeadingAttr kvs')
      return $
        Div divattr (Header level' hattr title' : sectionContents') : rest'
    go (Div divattr@(dident,dclasses,_) (Header level hattr title':ys) : xs)
        | all (\case
                 Header level' _ _ -> level' > level
                 _                 -> True) ys
        , "column" `notElem` dclasses
        , "columns" `notElem` dclasses
        , "fragment" `notElem` dclasses = do
      inner <- go (Header level hattr title':ys)
      rest <- go xs
      return $
        case inner of
              [Div divattr'@(dident',_,_) zs]
                | T.null dident || T.null dident' || dident == dident'
                -> Div (combineAttr divattr' divattr) zs : rest
              _ -> Div divattr inner : rest
    go (Div attr xs : rest) = do
      xs' <- go xs
      rest' <- go rest
      return $ Div attr xs' : rest'
    go (x:xs) = (x :) <$> go xs
    go [] = return []
  
  -- | Combine two 'Attr'. Classes are concatenated.  For the id and key-value
  -- attributes, the first one takes precedence in case of duplicates.
  combineAttr :: Attr -> Attr -> Attr
  combineAttr (id1, classes1, kvs1) (id2, classes2, kvs2) =
    (if T.null id1 then id2 else id1,
     nubOrd (classes1 ++ classes2),
     foldr (\(k,v) kvs -> case lookup k kvs of
                             Nothing -> (k,v):kvs
                             Just _  -> kvs) kvs1 kvs2)
  
  headerLtEq :: Int -> Block -> Bool
  headerLtEq level (Header l _ _)  = l <= level
  headerLtEq level (Div _ (b:_))   = headerLtEq level b
  headerLtEq _ _                   = False
  
  -- | Generate a unique identifier from a list of inlines.
  -- Second argument is a list of already used identifiers.
  uniqueIdent :: Extensions -> [Inline] -> Set.Set T.Text -> T.Text
  uniqueIdent exts title' usedIdents =
    if baseIdent `Set.member` usedIdents
       then maybe baseIdent numIdent
            $ find (\x -> numIdent x `Set.notMember` usedIdents) ([1..60000] :: [Int])
            -- if we have more than 60,000, allow repeats
       else baseIdent
    where
      baseIdent = case inlineListToIdentifier exts title' of
                       "" -> "section"
                       x  -> x
      numIdent n = baseIdent <> "-" <> tshow n
  
  -- | True if block is a Header block.
  isHeaderBlock :: Block -> Bool
  isHeaderBlock Header{} = True
  isHeaderBlock _        = False
  
  -- | Detect if table rows contain only cells consisting of a single
  -- paragraph that has no @LineBreak@.
  onlySimpleTableCells :: [[[Block]]] -> Bool
  onlySimpleTableCells = all isSimpleCell . concat
    where
      isSimpleCell [Plain ils] = not (hasLineBreak ils)
      isSimpleCell [Para ils ] = not (hasLineBreak ils)
      isSimpleCell []          = True
      isSimpleCell _           = False
      hasLineBreak = getAny . query isLineBreak
      isLineBreak LineBreak = Any True
      isLineBreak _         = Any False
  
  -- | Detect if a list is tight.
  isTightList :: [[Block]] -> Bool
  isTightList = all isPlainItem
    where
      isPlainItem [] = True
      isPlainItem (Plain _ : _) = True
      isPlainItem [BulletList xs] = isTightList xs
      isPlainItem [OrderedList _ xs] = isTightList xs
      isPlainItem _ = False
  
  -- | Convert a list item containing tasklist syntax (e.g. @[x]@)
  -- to using @U+2610 BALLOT BOX@ or @U+2612 BALLOT BOX WITH X@.
  taskListItemFromAscii :: Extensions -> [Block] -> [Block]
  taskListItemFromAscii = handleTaskListItem fromMd
    where
      fromMd (Str "[" : Space : Str "]" : Space : is) = Str "☐" : Space : is
      fromMd (Str "[x]"                 : Space : is) = Str "☒" : Space : is
      fromMd (Str "[X]"                 : Space : is) = Str "☒" : Space : is
      fromMd is = is
  
  -- | Convert a list item containing text starting with @U+2610 BALLOT BOX@
  -- or @U+2612 BALLOT BOX WITH X@ to tasklist syntax (e.g. @[x]@).
  taskListItemToAscii :: Extensions -> [Block] -> [Block]
  taskListItemToAscii = handleTaskListItem toMd
    where
      toMd (Str "☐" : Space : is) = rawMd "[ ]" : Space : is
      toMd (Str "☒" : Space : is) = rawMd "[x]" : Space : is
      toMd (Str "❏" : Space : is) = rawMd "[ ]" : Space : is
      toMd (Str "✓" : Space : is) = rawMd "[x]" : Space : is
      toMd is = is
      rawMd = RawInline (Format "markdown")
  
  handleTaskListItem :: ([Inline] -> [Inline]) -> Extensions -> [Block] -> [Block]
  handleTaskListItem handleInlines exts bls =
    if Ext_task_lists `extensionEnabled` exts
    then handleItem bls
    else bls
    where
      handleItem (Plain is : bs) = Plain (handleInlines is) : bs
      handleItem (Para is  : bs) = Para  (handleInlines is) : bs
      handleItem bs = bs
  
  -- | Set a field of a 'Meta' object.  If the field already has a value,
  -- convert it into a list with the new value appended to the old value(s).
  addMetaField :: ToMetaValue a
               => T.Text
               -> a
               -> Meta
               -> Meta
  addMetaField key val (Meta meta) =
    Meta $ M.insertWith combine key (toMetaValue val) meta
    where combine newval (MetaList xs) = MetaList (xs ++ tolist newval)
          combine newval x             = MetaList [x, newval]
          tolist (MetaList ys) = ys
          tolist y             = [y]
  
  -- | Set of HTML elements that are represented as Span with a class equal as
  -- the element tag itself.
  htmlSpanLikeElements :: Set.Set T.Text
  htmlSpanLikeElements = Set.fromList ["kbd", "mark", "dfn", "abbr"]
  
  -- | Reformat 'Inlines' as code, putting the stringlike parts in 'Code'
  -- elements while bringing other inline formatting outside.
  -- The idea is that e.g. `[Str "a",Space,Strong [Str "b"]]` should turn
  -- into `[Code ("",[],[]) "a ", Strong [Code ("",[],[]) "b"]]`.
  -- This helps work around the limitation that pandoc's Code element can
  -- only contain string content (see issue #7525).
  formatCode :: Attr -> Inlines -> Inlines
  formatCode attr = B.fromList . walk fmt . B.toList
    where
      isPlaintext (Str _) = True
      isPlaintext Space = True
      isPlaintext SoftBreak = True
      isPlaintext (Quoted _ _) = True
      isPlaintext _ = False
      fmt = concatMap go . groupBy (\a b -> isPlaintext a && isPlaintext b)
        where
          go xs
            | all isPlaintext xs = B.toList $ B.codeWith attr $ stringify xs
            | otherwise = xs
  
  --
  -- TagSoup HTML handling
  --
  
  -- | Render HTML tags.
  renderTags' :: [Tag T.Text] -> T.Text
  renderTags' = renderTagsOptions
                 renderOptions{ optMinimize = matchTags ["hr", "br", "img",
                                                         "meta", "link", "col",
                                                         "use", "path", "rect"]
                              , optRawTag   = matchTags ["script", "style"] }
                where matchTags tags = flip elem tags . T.toLower
  
  --
  -- File handling
  --
  
  -- | Perform an IO action in a directory, returning to starting directory.
  inDirectory :: FilePath -> IO a -> IO a
  inDirectory path action = E.bracket
                               getCurrentDirectory
                               setCurrentDirectory
                               (const $ setCurrentDirectory path >> action)
  
  -- | Canonicalizes a file path by removing redundant @.@ and @..@.
  makeCanonical :: FilePath -> FilePath
  makeCanonical = Posix.joinPath . transformPathParts . splitDirectories
   where  transformPathParts = reverse . foldl' go []
          go as        "."  = as
          go ("..":as) ".." = ["..", ".."] <> as
          go (_:as)    ".." = as
          go as        x    = x : as
  
  -- | Remove intermediate "." and ".." directories from a path.
  --
  -- > collapseFilePath "./foo" == "foo"
  -- > collapseFilePath "/bar/../baz" == "/baz"
  -- > collapseFilePath "/../baz" == "/../baz"
  -- > collapseFilePath "parent/foo/baz/../bar" ==  "parent/foo/bar"
  -- > collapseFilePath "parent/foo/baz/../../bar" ==  "parent/bar"
  -- > collapseFilePath "parent/foo/.." ==  "parent"
  -- > collapseFilePath "/parent/foo/../../bar" ==  "/bar"
  collapseFilePath :: FilePath -> FilePath
  collapseFilePath = Posix.joinPath . reverse . foldl' go [] . splitDirectories
    where
      go rs "." = rs
      go r@(p:rs) ".." = case p of
                              ".."                              -> "..":r
                              (checkPathSeperator -> Just True) -> "..":r
                              _                                 -> rs
      go _ (checkPathSeperator -> Just True) = [[Posix.pathSeparator]]
      go rs x = x:rs
      isSingleton []  = Nothing
      isSingleton [x] = Just x
      isSingleton _   = Nothing
      checkPathSeperator = fmap isPathSeparator . isSingleton
  
  --
  -- File selection from the archive
  --
  filteredFilesFromArchive :: Archive -> (FilePath -> Bool) -> [(FilePath, BL.ByteString)]
  filteredFilesFromArchive zf f =
    mapMaybe (fileAndBinary zf) (filter f (filesInArchive zf))
    where
      fileAndBinary :: Archive -> FilePath -> Maybe (FilePath, BL.ByteString)
      fileAndBinary a fp = findEntryByPath fp a >>= \e -> Just (fp, fromEntry e)
  
  ---
  --- Squash blocks into inlines
  ---
  
  blockToInlines :: Block -> Inlines
  blockToInlines (Plain ils) = B.fromList ils
  blockToInlines (Para ils) = B.fromList ils
  blockToInlines (LineBlock lns) = B.fromList $ combineLines lns
  blockToInlines (CodeBlock attr str) = B.codeWith attr str
  blockToInlines (RawBlock (Format fmt) str) = B.rawInline fmt str
  blockToInlines (BlockQuote blks) = blocksToInlines' blks
  blockToInlines (OrderedList _ blkslst) =
    mconcat $ map blocksToInlines' blkslst
  blockToInlines (BulletList blkslst) =
    mconcat $ map blocksToInlines' blkslst
  blockToInlines (DefinitionList pairslst) =
    mconcat $ map f pairslst
    where
      f (ils, blkslst) = B.fromList ils <> B.str ":" <> B.space <>
        mconcat (map blocksToInlines' blkslst)
  blockToInlines (Header _ _  ils) = B.fromList ils
  blockToInlines HorizontalRule = mempty
  blockToInlines (Table _ _ _ (TableHead _ hbd) bodies (TableFoot _ fbd)) =
    mconcat $ intersperse B.linebreak $
      map (mconcat . map blocksToInlines') (plainRowBody <$> hbd <> unTableBodies bodies <> fbd)
    where
      plainRowBody (Row _ body) = cellBody <$> body
      cellBody (Cell _ _ _ _ body) = body
      unTableBody (TableBody _ _ hd bd) = hd <> bd
      unTableBodies = concatMap unTableBody
  blockToInlines (Div _ blks) = blocksToInlines' blks
  blockToInlines (Figure _ _ body) = blocksToInlines' body
  
  blocksToInlinesWithSep :: Inlines -> [Block] -> Inlines
  blocksToInlinesWithSep sep =
    mconcat . intersperse sep . map blockToInlines
  
  blocksToInlines' :: [Block] -> Inlines
  blocksToInlines' = blocksToInlinesWithSep defaultBlocksSeparator
  
  blocksToInlines :: [Block] -> [Inline]
  blocksToInlines = B.toList . blocksToInlines'
  
  -- | Inline elements used to separate blocks when squashing blocks into
  -- inlines.
  defaultBlocksSeparator :: Inlines
  defaultBlocksSeparator =
    -- This is used in the pandoc.utils.blocks_to_inlines function. Docs
    -- there should be updated if this is changed.
    B.linebreak
  
  --
  -- Safe read
  --
  
  safeRead :: (MonadPlus m, Read a) => T.Text -> m a
  safeRead = safeStrRead . T.unpack
  
  safeStrRead :: (MonadPlus m, Read a) => String -> m a
  safeStrRead s = case reads s of
                    (d,x):_
                      | all isSpace x -> return d
                    _                 -> mzero
  