pandoc/src/Text/Pandoc/Shared.hs

{-# LANGUAGE CPP                   #-}
{-# LANGUAGE DeriveDataTypeable    #-}
{-# LANGUAGE FlexibleContexts      #-}
{-# LANGUAGE MultiParamTypeClasses #-}

{-# LANGUAGE ScopedTypeVariables   #-}
{-# LANGUAGE ViewPatterns          #-}
{-
Copyright (C) 2006-2017 John MacFarlane <jgm@berkeley.edu>

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
-}

{- |
   Module      : Text.Pandoc.Shared
   Copyright   : Copyright (C) 2006-2017 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,
                     splitByIndices,
                     splitStringByIndices,
                     substitute,
                     ordNub,
                     -- * Text processing
                     backslashEscapes,
                     escapeStringUsing,
                     stripTrailingNewlines,
                     trim,
                     triml,
                     trimr,
                     stripFirstAndLast,
                     camelCaseToHyphenated,
                     toRomanNumeral,
                     escapeURI,
                     tabFilter,
                     crFilter,
                     -- * Date/time
                     normalizeDate,
                     -- * Pandoc block and inline list processing
                     orderedListMarkers,
                     extractSpaces,
                     removeFormatting,
                     deNote,
                     stringify,
                     capitalize,
                     compactify,
                     compactifyDL,
                     linesToPara,
                     Element (..),
                     hierarchicalize,
                     uniqueIdent,
                     inlineListToIdentifier,
                     isHeaderBlock,
                     headerShift,
                     isTightList,
                     addMetaField,
                     makeMeta,
                     eastAsianLineBreakFilter,
                     underlineSpan,
                     -- * TagSoup HTML handling
                     renderTags',
                     -- * File handling
                     inDirectory,
                     collapseFilePath,
                     filteredFilesFromArchive,
                     -- * URI handling
                     schemes,
                     isURI,
                     -- * Error handling
                     mapLeft,
                     -- * for squashing blocks
                     blocksToInlines,
                     -- * Safe read
                     safeRead,
                     -- * Temp directory
                     withTempDir,
                     -- * Version
                     pandocVersion
                    ) 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.Char (isAlpha, isDigit, isLetter, isLower, isSpace, isUpper,
                  toLower)
import Data.Data (Data, Typeable)
import Data.List (find, intercalate, stripPrefix)
import qualified Data.Map as M
import Data.Maybe (mapMaybe)
import Data.Monoid ((<>))
import Data.Sequence (ViewL (..), ViewR (..), viewl, viewr)
import qualified Data.Set as Set
import qualified Data.Text as T
import Data.Version (showVersion)
import Network.URI (URI (uriScheme), escapeURIString, parseURI)
import Paths_pandoc (version)
import System.Directory
import System.FilePath (isPathSeparator, splitDirectories)
import qualified System.FilePath.Posix as Posix
import System.IO.Temp
import Text.HTML.TagSoup (RenderOptions (..), Tag (..), renderOptions,
                          renderTagsOptions)
import Text.Pandoc.Builder (Blocks, Inlines, ToMetaValue (..))
import qualified Text.Pandoc.Builder as B
import Text.Pandoc.Compat.Time
import Text.Pandoc.Definition
import Text.Pandoc.Generic (bottomUp)
import Text.Pandoc.Pretty (charWidth)
import Text.Pandoc.Walk

-- | Version number of pandoc library.
pandocVersion :: String
pandocVersion = showVersion version

--
-- 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
      rest'         = dropWhile isSep rest
  in  first:splitBy isSep rest'

splitByIndices :: [Int] -> [a] -> [[a]]
splitByIndices [] lst = [lst]
splitByIndices (x:xs) lst = first:splitByIndices (map (\y -> y - x)  xs) rest
  where (first, rest) = splitAt x lst

-- | Split string into chunks divided at specified indices.
splitStringByIndices :: [Int] -> [Char] -> [[Char]]
splitStringByIndices [] lst = [lst]
splitStringByIndices (x:xs) lst =
  let (first, rest) = splitAt' x lst in
  first : splitStringByIndices (map (\y -> y - x) xs) rest

splitAt' :: Int -> [Char] -> ([Char],[Char])
splitAt' _ []          = ([],[])
splitAt' n xs | n <= 0 = ([],xs)
splitAt' n (x:xs)      = (x:ys,zs)
  where (ys,zs) = splitAt' (n - charWidth x) xs

-- | Replace each occurrence of one sublist in a list with another.
substitute :: (Eq a) => [a] -> [a] -> [a] -> [a]
substitute _ _ [] = []
substitute [] _ xs = xs
substitute target replacement lst@(x:xs) =
    case stripPrefix target lst of
      Just lst' -> replacement ++ substitute target replacement lst'
      Nothing   -> x : substitute target replacement xs

ordNub :: (Ord a) => [a] -> [a]
ordNub l = go Set.empty l
  where
    go _ [] = []
    go s (x:xs) = if x `Set.member` s then go s xs
                                      else x : go (Set.insert x s) xs

--
-- Text processing
--

-- | Returns an association list of backslash escapes for the
-- designated characters.
backslashEscapes :: [Char]    -- ^ list of special characters to escape
                 -> [(Char, String)]
backslashEscapes = map (\ch -> (ch, ['\\',ch]))

-- | Escape a string of characters, using an association list of
-- characters and strings.
escapeStringUsing :: [(Char, String)] -> String -> String
escapeStringUsing _ [] = ""
escapeStringUsing escapeTable (x:xs) =
  case lookup x escapeTable of
       Just str -> str ++ rest
       Nothing  -> x:rest
  where rest = escapeStringUsing escapeTable xs

-- | Strip trailing newlines from string.
stripTrailingNewlines :: String -> String
stripTrailingNewlines = reverse . dropWhile (== '\n') . reverse

-- | Remove leading and trailing space (including newlines) from string.
trim :: String -> String
trim = triml . trimr

-- | Remove leading space (including newlines) from string.
triml :: String -> String
triml = dropWhile (`elem` " \r\n\t")

-- | Remove trailing space (including newlines) from string.
trimr :: String -> String
trimr = reverse . triml . reverse

-- | Strip leading and trailing characters from string
stripFirstAndLast :: String -> String
stripFirstAndLast str =
  drop 1 $ take (length str - 1) str

-- | Change CamelCase word to hyphenated lowercase (e.g., camel-case).
camelCaseToHyphenated :: String -> String
camelCaseToHyphenated [] = ""
camelCaseToHyphenated (a:b:rest) | isLower a && isUpper b =
  a:'-':toLower b:camelCaseToHyphenated rest
camelCaseToHyphenated (a:rest) = toLower a:camelCaseToHyphenated rest

-- | Convert number < 4000 to uppercase roman numeral.
toRomanNumeral :: Int -> String
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 = ""

-- | Escape whitespace and some punctuation characters in URI.
escapeURI :: String -> String
escapeURI = escapeURIString (not . needsEscaping)
  where needsEscaping c = isSpace c || c `elem`
                           ['<','>','|','"','{','}','[',']','^', '`']

-- | 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)

-- | Strip out DOS line endings.
crFilter :: T.Text -> T.Text
crFilter = T.filter (/= '\r')

--
-- 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 :: 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 =
#if MIN_VERSION_time(1,5,0)
             parseTimeM True defaultTimeLocale
#else
             parseTime defaultTimeLocale
#endif
        formats = ["%x","%m/%d/%Y", "%D","%F", "%d %b %Y",
                    "%d %B %Y", "%b. %d, %Y", "%B %d, %Y",
                    "%Y%m%d", "%Y%m", "%Y"]

--
-- Pandoc block and inline list processing
--

-- | Generate infinite lazy list of markers for an ordered list,
-- depending on list attributes.
orderedListMarkers :: (Int, ListNumberStyle, ListNumberDelim) -> [String]
orderedListMarkers (start, numstyle, numdelim) =
  let singleton c = [c]
      nums = case numstyle of
                     DefaultStyle -> map show [start..]
                     Example      -> map show [start..]
                     Decimal      -> map show [start..]
                     UpperAlpha   -> drop (start - 1) $ cycle $
                                     map singleton ['A'..'Z']
                     LowerAlpha   -> drop (start - 1) $ cycle $
                                     map singleton ['a'..'z']
                     UpperRoman   -> map toRomanNumeral [start..]
                     LowerRoman   -> map (map 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 _          = []

deNote :: Inline -> Inline
deNote (Note _) = Str ""
deNote x        = x

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

-- | 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 -> String
stringify = query go . walk (deNote . deQuote)
  where go :: Inline -> [Char]
        go Space                                       = " "
        go SoftBreak                                   = " "
        go (Str x)                                     = x
        go (Code _ x)                                  = x
        go (Math _ x)                                  = x
        go (RawInline (Format "html") ('<':'b':'r':_)) = " " -- see #2105
        go LineBreak                                   = " "
        go _                                           = ""

-- | 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.unpack $ T.toUpper $ T.pack s)
        go x       = x

-- | Change final list item from @Para@ to @Plain@ if the list contains
-- no other @Para@ blocks.  Like compactify, but operates on @Blocks@ rather
-- than @[Block]@.
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) -> case [Para x | Para x <- concatMap B.toList items] of
                            -- if this is only Para, change to Plain
                            [_] -> others ++ [B.fromList (reverse $ Plain a : xs)]
                            _   -> items
           _      -> items

-- | Like @compactify@, but acts on items of definition lists.
compactifyDL :: [(Inlines, [Blocks])] -> [(Inlines, [Blocks])]
compactifyDL items =
  let defs = concatMap snd items
  in  case reverse (concatMap B.toList defs) of
           (Para x:xs)
             | not (any isPara xs) ->
                   let (t,ds) = last items
                       lastDef = B.toList $ last ds
                       ds' = init ds ++
                             if null lastDef
                                then [B.fromList lastDef]
                                else [B.fromList $ init lastDef ++ [Plain x]]
                    in init items ++ [(t, ds')]
             | otherwise           -> 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

isPara :: Block -> Bool
isPara (Para _) = True
isPara _        = False

-- | Data structure for defining hierarchical Pandoc documents
data Element = Blk Block
             | Sec Int [Int] Attr [Inline] [Element]
             --    lvl  num attributes label    contents
             deriving (Eq, Read, Show, Typeable, Data)

instance Walkable Inline Element where
  walk f (Blk x) = Blk (walk f x)
  walk f (Sec lev nums attr ils elts) = Sec lev nums attr (walk f ils) (walk f elts)
  walkM f (Blk x) = Blk `fmap` walkM f x
  walkM f (Sec lev nums attr ils elts) = do
    ils' <- walkM f ils
    elts' <- walkM f elts
    return $ Sec lev nums attr ils' elts'
  query f (Blk x)              = query f x
  query f (Sec _ _ _ ils elts) = query f ils <> query f elts

instance Walkable Block Element where
  walk f (Blk x) = Blk (walk f x)
  walk f (Sec lev nums attr ils elts) = Sec lev nums attr (walk f ils) (walk f elts)
  walkM f (Blk x) = Blk `fmap` walkM f x
  walkM f (Sec lev nums attr ils elts) = do
    ils' <- walkM f ils
    elts' <- walkM f elts
    return $ Sec lev nums attr ils' elts'
  query f (Blk x)              = query f x
  query f (Sec _ _ _ ils elts) = query f ils <> query f elts


-- | Convert Pandoc inline list to plain text identifier.  HTML
-- identifiers must start with a letter, and may contain only
-- letters, digits, and the characters _-.
inlineListToIdentifier :: [Inline] -> String
inlineListToIdentifier =
  dropWhile (not . isAlpha) . intercalate "-" . words .
    map (nbspToSp . toLower) .
    filter (\c -> isLetter c || isDigit c || c `elem` "_-. ") .
    stringify
 where nbspToSp '\160' =  ' '
       nbspToSp x      =  x

-- | Convert list of Pandoc blocks into (hierarchical) list of Elements
hierarchicalize :: [Block] -> [Element]
hierarchicalize blocks = S.evalState (hierarchicalizeWithIds blocks) []

hierarchicalizeWithIds :: [Block] -> S.State [Int] [Element]
hierarchicalizeWithIds [] = return []
hierarchicalizeWithIds (Header level attr@(_,classes,_) title':xs) = do
  lastnum <- S.get
  let lastnum' = take level lastnum
  let newnum = case length lastnum' of
                    x | "unnumbered" `elem` classes -> []
                      | x >= level -> init lastnum' ++ [last lastnum' + 1]
                      | otherwise -> lastnum ++
                           replicate (level - length lastnum - 1) 0 ++ [1]
  unless (null newnum) $ S.put newnum
  let (sectionContents, rest) = break (headerLtEq level) xs
  sectionContents' <- hierarchicalizeWithIds sectionContents
  rest' <- hierarchicalizeWithIds rest
  return $ Sec level newnum attr title' sectionContents' : rest'
hierarchicalizeWithIds (Div ("",["references"],[])
                         (Header level (ident,classes,kvs) title' : xs):ys) =
  hierarchicalizeWithIds (Header level (ident,("references":classes),kvs)
                           title' : (xs ++ ys))
hierarchicalizeWithIds (x:rest) = do
  rest' <- hierarchicalizeWithIds rest
  return $ Blk x : rest'

headerLtEq :: Int -> Block -> Bool
headerLtEq level (Header l _ _)                                  = l <= level
headerLtEq level (Div ("",["references"],[]) (Header l _ _ : _)) = l <= level
headerLtEq _ _                                                   = False

-- | Generate a unique identifier from a list of inlines.
-- Second argument is a list of already used identifiers.
uniqueIdent :: [Inline] -> Set.Set String -> String
uniqueIdent title' usedIdents
  =  let baseIdent = case inlineListToIdentifier title' of
                        "" -> "section"
                        x  -> x
         numIdent n = baseIdent ++ "-" ++ show n
     in  if baseIdent `Set.member` usedIdents
           then case find (\x -> not $ numIdent x `Set.member` usedIdents) ([1..60000] :: [Int]) of
                  Just x  -> numIdent x
                  Nothing -> baseIdent   -- if we have more than 60,000, allow repeats
           else baseIdent

-- | True if block is a Header block.
isHeaderBlock :: Block -> Bool
isHeaderBlock Header{} = True
isHeaderBlock _        = False

-- | Shift header levels up or down.
headerShift :: Int -> Pandoc -> Pandoc
headerShift n = walk shift
  where shift :: Block -> Block
        shift (Header level attr inner) = Header (level + n) attr inner
        shift x                         = x

-- | Detect if a list is tight.
isTightList :: [[Block]] -> Bool
isTightList = all firstIsPlain
  where firstIsPlain (Plain _ : _) = True
        firstIsPlain _             = False

-- | 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
             => String
             -> 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]

-- | Create 'Meta' from old-style title, authors, date.  This is
-- provided to ease the transition from the old API.
makeMeta :: [Inline] -> [[Inline]] -> [Inline] -> Meta
makeMeta title authors date =
      addMetaField "title" (B.fromList title)
    $ addMetaField "author" (map B.fromList authors)
    $ addMetaField "date" (B.fromList date) nullMeta

-- | Remove soft breaks between East Asian characters.
eastAsianLineBreakFilter :: Pandoc -> Pandoc
eastAsianLineBreakFilter = bottomUp go
  where go (x:SoftBreak:y:zs) =
         case (stringify x, stringify y) of
               (xs@(_:_), c:_)
                 | charWidth (last xs) == 2 && charWidth c == 2 -> x:y:zs
               _ -> x:SoftBreak:y:zs
        go xs = xs

-- | Builder for underline.
-- This probably belongs in Builder.hs in pandoc-types.
-- Will be replaced once Underline is an element.
underlineSpan :: Inlines -> Inlines
underlineSpan = B.spanWith ("", ["underline"], [])


--
-- TagSoup HTML handling
--

-- | Render HTML tags.
renderTags' :: [Tag String] -> String
renderTags' = renderTagsOptions
               renderOptions{ optMinimize = matchTags ["hr", "br", "img",
                                                       "meta", "link"]
                            , optRawTag   = matchTags ["script", "style"] }
              where matchTags tags = flip elem tags . map 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)

--
-- Error reporting
--

mapLeft :: (a -> b) -> Either a c -> Either b c
mapLeft f (Left x)  = Left (f x)
mapLeft _ (Right x) = Right x

-- | 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)


--
-- IANA URIs
--

-- | Schemes from http://www.iana.org/assignments/uri-schemes.html plus
-- the unofficial schemes doi, javascript, isbn, pmid.
schemes :: Set.Set String
schemes = Set.fromList
  -- Official IANA schemes
  [ "aaa", "aaas", "about", "acap", "acct", "acr", "adiumxtra", "afp", "afs"
  , "aim", "appdata", "apt", "attachment", "aw", "barion", "beshare", "bitcoin"
  , "blob", "bolo", "browserext", "callto", "cap", "chrome", "chrome-extension"
  , "cid", "coap", "coaps", "com-eventbrite-attendee", "content", "crid", "cvs"
  , "data", "dav", "dict", "dis", "dlna-playcontainer", "dlna-playsingle"
  , "dns", "dntp", "dtn", "dvb", "ed2k", "example", "facetime", "fax", "feed"
  , "feedready", "file", "filesystem", "finger", "fish", "ftp", "geo", "gg"
  , "git", "gizmoproject", "go", "gopher", "graph", "gtalk", "h323", "ham"
  , "hcp", "http", "https", "hxxp", "hxxps", "hydrazone", "iax", "icap", "icon"
  , "im", "imap", "info", "iotdisco", "ipn", "ipp", "ipps", "irc", "irc6"
  , "ircs", "iris", "iris.beep", "iris.lwz", "iris.xpc", "iris.xpcs"
  , "isostore", "itms", "jabber", "jar", "jms", "keyparc", "lastfm", "ldap"
  , "ldaps", "lvlt", "magnet", "mailserver", "mailto", "maps", "market"
  , "message", "mid", "mms", "modem", "mongodb", "moz", "ms-access"
  , "ms-browser-extension", "ms-drive-to", "ms-enrollment", "ms-excel"
  , "ms-gamebarservices", "ms-getoffice", "ms-help", "ms-infopath"
  , "ms-media-stream-id", "ms-officeapp", "ms-project", "ms-powerpoint"
  , "ms-publisher", "ms-search-repair", "ms-secondary-screen-controller"
  , "ms-secondary-screen-setup", "ms-settings", "ms-settings-airplanemode"
  , "ms-settings-bluetooth", "ms-settings-camera", "ms-settings-cellular"
  , "ms-settings-cloudstorage", "ms-settings-connectabledevices"
  , "ms-settings-displays-topology", "ms-settings-emailandaccounts"
  , "ms-settings-language", "ms-settings-location", "ms-settings-lock"
  , "ms-settings-nfctransactions", "ms-settings-notifications"
  , "ms-settings-power", "ms-settings-privacy", "ms-settings-proximity"
  , "ms-settings-screenrotation", "ms-settings-wifi", "ms-settings-workplace"
  , "ms-spd", "ms-sttoverlay", "ms-transit-to", "ms-virtualtouchpad"
  , "ms-visio", "ms-walk-to", "ms-whiteboard", "ms-whiteboard-cmd", "ms-word"
  , "msnim", "msrp", "msrps", "mtqp", "mumble", "mupdate", "mvn", "news", "nfs"
  , "ni", "nih", "nntp", "notes", "ocf", "oid", "onenote", "onenote-cmd"
  , "opaquelocktoken", "pack", "palm", "paparazzi", "pkcs11", "platform", "pop"
  , "pres", "prospero", "proxy", "pwid", "psyc", "qb", "query", "redis"
  , "rediss", "reload", "res", "resource", "rmi", "rsync", "rtmfp", "rtmp"
  , "rtsp", "rtsps", "rtspu", "secondlife", "service", "session", "sftp", "sgn"
  , "shttp", "sieve", "sip", "sips", "skype", "smb", "sms", "smtp", "snews"
  , "snmp", "soap.beep", "soap.beeps", "soldat", "spotify", "ssh", "steam"
  , "stun", "stuns", "submit", "svn", "tag", "teamspeak", "tel", "teliaeid"
  , "telnet", "tftp", "things", "thismessage", "tip", "tn3270", "tool", "turn"
  , "turns", "tv", "udp", "unreal", "urn", "ut2004", "v-event", "vemmi"
  , "ventrilo", "videotex", "vnc", "view-source", "wais", "webcal", "wpid"
  , "ws", "wss", "wtai", "wyciwyg", "xcon", "xcon-userid", "xfire"
  , "xmlrpc.beep", "xmlrpc.beeps", "xmpp", "xri", "ymsgr", "z39.50", "z39.50r"
  , "z39.50s"
  -- Inofficial schemes
  , "doi", "isbn", "javascript", "pmid"
  ]

-- | Check if the string is a valid URL with a IANA or frequently used but
-- unofficial scheme (see @schemes@).
isURI :: String -> Bool
isURI = maybe False hasKnownScheme . parseURI
  where
    hasKnownScheme = (`Set.member` schemes) . map toLower .
                     filter (/= ':') . uriScheme

---
--- Squash blocks into inlines
---

blockToInlines :: Block -> [Inline]
blockToInlines (Plain ils) = ils
blockToInlines (Para ils) = ils
blockToInlines (LineBlock lns) = combineLines lns
blockToInlines (CodeBlock attr str) = [Code attr str]
blockToInlines (RawBlock fmt str) = [RawInline fmt str]
blockToInlines (BlockQuote blks) = blocksToInlines blks
blockToInlines (OrderedList _ blkslst) =
  concatMap blocksToInlines blkslst
blockToInlines (BulletList blkslst) =
  concatMap blocksToInlines blkslst
blockToInlines (DefinitionList pairslst) =
  concatMap f pairslst
  where
    f (ils, blkslst) = ils ++
      [Str ":", Space] ++
      concatMap blocksToInlines blkslst
blockToInlines (Header _ _  ils) = ils
blockToInlines HorizontalRule = []
blockToInlines (Table _ _ _ headers rows) =
  intercalate [LineBreak] $ map (concatMap blocksToInlines) tbl
  where
    tbl = headers : rows
blockToInlines (Div _ blks) = blocksToInlines blks
blockToInlines Null = []

blocksToInlinesWithSep :: [Inline] -> [Block] -> [Inline]
blocksToInlinesWithSep sep blks = intercalate sep $ map blockToInlines blks

blocksToInlines :: [Block] -> [Inline]
blocksToInlines = blocksToInlinesWithSep [Space, Str "¶", Space]


--
-- Safe read
--

safeRead :: (MonadPlus m, Read a) => String -> m a
safeRead s = case reads s of
                  (d,x):_
                    | all isSpace x -> return d
                  _                 -> mzero

--
-- Temp directory
--

withTempDir :: String -> (FilePath -> IO a) -> IO a
withTempDir =
#ifdef _WINDOWS
  withTempDirectory "."
#else
  withSystemTempDirectory
#endif