{-# LANGUAGE CPP                 #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TupleSections       #-}
{-
Copyright (C) 2006-2016 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.App
   Copyright   : Copyright (C) 2006-2016 John MacFarlane
   License     : GNU GPL, version 2 or above

   Maintainer  : John MacFarlane <jgm@berkeley@edu>
   Stability   : alpha
   Portability : portable

Does a pandoc conversion based on command-line options.
-}
module Text.Pandoc.App (
            convertWithOpts
          , Opt(..)
          , defaultOpts
          , parseOptions
          , options
          ) where
import Control.Applicative ((<|>))
import qualified Control.Exception as E
import Control.Monad
import Control.Monad.Trans
import Data.Aeson (eitherDecode', encode)
import qualified Data.ByteString as BS
import qualified Data.ByteString.Lazy as B
import Data.Char (toLower, toUpper)
import qualified Data.Set as Set
import Data.Foldable (foldrM)
import Data.List (intercalate, isPrefixOf, isSuffixOf, sort)
import qualified Data.Map as M
import Data.Maybe (fromMaybe, isJust, isNothing)
import qualified Data.Text as T
import Data.Yaml (decode)
import qualified Data.Yaml as Yaml
import Network.URI (URI (..), isURI, parseURI)
import Paths_pandoc (getDataDir)
import Skylighting (Style, Syntax (..), defaultSyntaxMap, parseTheme)
import Skylighting.Parser (missingIncludes, parseSyntaxDefinition,
                           addSyntaxDefinition)
import System.Console.GetOpt
import System.Directory (Permissions (..), doesFileExist, findExecutable,
                         getAppUserDataDirectory, getPermissions)
import System.Environment (getArgs, getEnvironment, getProgName)
import System.Exit (ExitCode (..), exitSuccess)
import System.FilePath
import System.IO (stderr, stdout)
import System.IO.Error (isDoesNotExistError)
import Text.Pandoc
import Text.Pandoc.Builder (setMeta)
import Text.Pandoc.Class (PandocIO, getLog, withMediaBag)
import Text.Pandoc.Highlighting (highlightingStyles)
import Text.Pandoc.Lua ( runLuaFilter )
import Text.Pandoc.MediaBag (MediaBag, extractMediaBag, mediaDirectory)
import Text.Pandoc.PDF (makePDF)
import Text.Pandoc.Process (pipeProcess)
import Text.Pandoc.SelfContained (makeSelfContained, makeDataURI)
import Text.Pandoc.Shared (headerShift, openURL, readDataFile,
                           readDataFileUTF8, safeRead, tabFilter)
import qualified Text.Pandoc.UTF8 as UTF8
import Text.Pandoc.Walk (walk)
import Text.Pandoc.XML (toEntities)
import Text.Printf
#ifndef _WINDOWS
import System.Posix.IO (stdOutput)
import System.Posix.Terminal (queryTerminal)
#endif

parseOptions :: [OptDescr (Opt -> IO Opt)] -> Opt -> IO Opt
parseOptions options' defaults = do
  rawArgs <- map UTF8.decodeArg <$> getArgs
  prg <- getProgName

  let (actions, args, unrecognizedOpts, errors) =
           getOpt' Permute options' rawArgs

  let unknownOptionErrors = foldr handleUnrecognizedOption [] unrecognizedOpts

  unless (null errors && null unknownOptionErrors) $
     E.throwIO $ PandocOptionError $
        concat errors ++ unlines unknownOptionErrors ++
        ("Try " ++ prg ++ " --help for more information.")

  -- thread option data structure through all supplied option actions
  opts <- foldl (>>=) (return defaults) actions
  return (opts{ optInputFiles = args })

convertWithOpts :: Opt -> IO ()
convertWithOpts opts = do
  let args = optInputFiles opts
  let outputFile = optOutputFile opts
  let filters = optFilters opts
  let verbosity = optVerbosity opts

  when (optDumpArgs opts) $
    do UTF8.hPutStrLn stdout outputFile
       mapM_ (UTF8.hPutStrLn stdout) args
       exitSuccess

  epubMetadata <- case optEpubMetadata opts of
                         Nothing -> return Nothing
                         Just fp -> Just <$> UTF8.readFile fp

  let csscdn = "https://cdnjs.cloudflare.com/ajax/libs/KaTeX/0.6.0/katex.min.css"
  let mathMethod =
        case (optKaTeXJS opts, optKaTeXStylesheet opts) of
            (Nothing, _)  -> optHTMLMathMethod opts
            (Just js, ss) -> KaTeX js (fromMaybe csscdn ss)


  -- --bibliography implies -F pandoc-citeproc for backwards compatibility:
  let needsCiteproc = isJust (lookup "bibliography" (optMetadata opts)) &&
                      optCiteMethod opts `notElem` [Natbib, Biblatex] &&
                      "pandoc-citeproc" `notElem` map takeBaseName filters
  let filters' = if needsCiteproc then "pandoc-citeproc" : filters
                                  else filters

  let sources = case args of
                     []  -> ["-"]
                     xs | optIgnoreArgs opts -> ["-"]
                        | otherwise  -> xs

  datadir <- case optDataDir opts of
                  Nothing   -> E.catch
                                 (Just <$> getAppUserDataDirectory "pandoc")
                                 (\e -> let _ = (e :: E.SomeException)
                                        in  return Nothing)
                  Just _    -> return $ optDataDir opts

  -- assign reader and writer based on options and filenames
  let readerName = case optReader opts of
                          Nothing -> defaultReaderName
                                      (if any isURI sources
                                          then "html"
                                          else "markdown") sources
                          Just x  -> map toLower x

  let writerName = case optWriter opts of
                          Nothing -> defaultWriterName outputFile
                          Just x  -> map toLower x
  let format = takeWhile (`notElem` ['+','-'])
                       $ takeFileName writerName  -- in case path to lua script

  let pdfOutput = map toLower (takeExtension outputFile) == ".pdf"

  let laTeXOutput = format `elem` ["latex", "beamer"]
  let conTeXtOutput = format == "context"
  let html5Output = format == "html5" || format == "html"
  let msOutput = format == "ms"

  -- disabling the custom writer for now
  writer <- if ".lua" `isSuffixOf` format
               -- note:  use non-lowercased version writerName
               then return (StringWriter
                       (\o d -> liftIO $ writeCustom writerName o d)
                               :: Writer PandocIO)
               else case getWriter writerName of
                         Left e  -> E.throwIO $ PandocAppError 9 $
                           if format == "pdf"
                              then e ++
                               "\nTo create a pdf using pandoc, use " ++
                               "-t latex|beamer|context|ms|html5" ++
                               "\nand specify an output file with " ++
                               ".pdf extension (-o filename.pdf)."
                              else e
                         Right w -> return (w :: Writer PandocIO)

  -- TODO: we have to get the input and the output into the state for
  -- the sake of the text2tags reader.
  reader <-  case getReader readerName of
                Right r  -> return (r :: Reader PandocIO)
                Left e   -> E.throwIO $ PandocAppError 7 e'
                  where e' = case readerName of
                                  "pdf" -> e ++
                                     "\nPandoc can convert to PDF, but not from PDF."
                                  "doc" -> e ++
                                     "\nPandoc can convert from DOCX, but not from DOC.\nTry using Word to save your DOC file as DOCX, and convert that with pandoc."
                                  _ -> e

  let standalone = optStandalone opts || not (isTextFormat format) || pdfOutput

  templ <- case optTemplate opts of
                _ | not standalone -> return Nothing
                Nothing -> do
                           deftemp <- getDefaultTemplate datadir format
                           case deftemp of
                                 Left e  -> E.throwIO e
                                 Right t -> return (Just t)
                Just tp -> do
                           -- strip off extensions
                           let tp' = case takeExtension tp of
                                          "" -> tp <.> format
                                          _  -> tp
                           Just <$> E.catch (UTF8.readFile tp')
                             (\e -> if isDoesNotExistError e
                                       then E.catch
                                             (readDataFileUTF8 datadir
                                                ("templates" </> tp'))
                                             (\e' -> let _ = (e' :: E.SomeException)
                                                     in E.throwIO e')
                                       else E.throwIO e)

  let addStringAsVariable varname s vars = return $ (varname, s) : vars

  let addContentsAsVariable varname fp vars = do
             s <- UTF8.readFile fp
             return $ (varname, s) : vars

  -- note: this reverses the list constructed in option parsing,
  -- which in turn was reversed from the command-line order,
  -- so we end up with the correct order in the variable list:
  let withList _ [] vars     = return vars
      withList f (x:xs) vars = f x vars >>= withList f xs

  variables <-
      return (("outputfile", optOutputFile opts) : optVariables opts)
      >>=
      withList (addStringAsVariable "sourcefile")
               (reverse $ optInputFiles opts)
               -- we reverse this list because, unlike
               -- the other option lists here, it is
               -- not reversed when parsed from CLI arguments.
               -- See withList, above.
      >>=
      withList (addContentsAsVariable "include-before")
               (optIncludeBeforeBody opts)
      >>=
      withList (addContentsAsVariable "include-after")
               (optIncludeAfterBody opts)
      >>=
      withList (addContentsAsVariable "header-includes")
               (optIncludeInHeader opts)
      >>=
      withList (addStringAsVariable "css") (optCss opts)
      >>=
      maybe return (addStringAsVariable "title-prefix") (optTitlePrefix opts)
      >>=
      maybe return (addStringAsVariable "epub-cover-image")
                   (optEpubCoverImage opts)
      >>=
      (\vars -> case mathMethod of
                     LaTeXMathML Nothing -> do
                        s <- readDataFileUTF8 datadir "LaTeXMathML.js"
                        return $ ("mathml-script", s) : vars
                     _ -> return vars)
      >>=
      (\vars ->  if format == "dzslides"
                    then do
                        dztempl <- readDataFileUTF8 datadir
                                     ("dzslides" </> "template.html")
                        let dzline = "<!-- {{{{ dzslides core"
                        let dzcore = unlines
                                   $ dropWhile (not . (dzline `isPrefixOf`))
                                   $ lines dztempl
                        return $ ("dzslides-core", dzcore) : vars
                    else return vars)

  let sourceURL = case sources of
                    []    -> Nothing
                    (x:_) -> case parseURI x of
                                Just u
                                  | uriScheme u `elem` ["http:","https:"] ->
                                      Just $ show u{ uriQuery = "",
                                                     uriFragment = "" }
                                _ -> Nothing

  abbrevs <- (Set.fromList . filter (not . null) . lines) <$>
             case optAbbreviations opts of
                  Nothing -> readDataFileUTF8 datadir "abbreviations"
                  Just f  -> UTF8.readFile f

  let readerOpts = def{ readerStandalone = standalone
                      , readerColumns = optColumns opts
                      , readerTabStop = optTabStop opts
                      , readerIndentedCodeClasses = optIndentedCodeClasses opts
                      , readerApplyMacros = not laTeXOutput
                      , readerDefaultImageExtension =
                         optDefaultImageExtension opts
                      , readerTrackChanges = optTrackChanges opts
                      , readerAbbreviations = abbrevs
                      }

  highlightStyle <- lookupHighlightStyle $ optHighlightStyle opts
  let addSyntaxMap existingmap f = do
        res <- parseSyntaxDefinition f
        case res of
              Left errstr -> E.throwIO $ PandocSyntaxMapError errstr
              Right syn   -> return $ addSyntaxDefinition syn existingmap

  syntaxMap <- foldM addSyntaxMap defaultSyntaxMap
                     (optSyntaxDefinitions opts)

  case missingIncludes (M.elems syntaxMap) of
       [] -> return ()
       xs -> E.throwIO $ PandocSyntaxMapError $
                "Missing syntax definitions:\n" ++
                unlines (map
                  (\(syn,dep) -> (T.unpack syn ++ " requires " ++
                    T.unpack dep ++ " through IncludeRules.")) xs)

  let writerOptions = def { writerTemplate         = templ,
                            writerVariables        = variables,
                            writerTabStop          = optTabStop opts,
                            writerTableOfContents  = optTableOfContents opts,
                            writerHTMLMathMethod   = mathMethod,
                            writerIncremental      = optIncremental opts,
                            writerCiteMethod       = optCiteMethod opts,
                            writerNumberSections   = optNumberSections opts,
                            writerNumberOffset     = optNumberOffset opts,
                            writerSectionDivs      = optSectionDivs opts,
                            writerReferenceLinks   = optReferenceLinks opts,
                            writerReferenceLocation = optReferenceLocation opts,
                            writerDpi              = optDpi opts,
                            writerWrapText         = optWrapText opts,
                            writerColumns          = optColumns opts,
                            writerEmailObfuscation = optEmailObfuscation opts,
                            writerIdentifierPrefix = optIdentifierPrefix opts,
                            writerSourceURL        = sourceURL,
                            writerUserDataDir      = datadir,
                            writerHtmlQTags        = optHtmlQTags opts,
                            writerTopLevelDivision = optTopLevelDivision opts,
                            writerListings         = optListings opts,
                            writerSlideLevel       = optSlideLevel opts,
                            writerHighlightStyle   = highlightStyle,
                            writerSetextHeaders    = optSetextHeaders opts,
                            writerEpubMetadata     = epubMetadata,
                            writerEpubFonts        = optEpubFonts opts,
                            writerEpubChapterLevel = optEpubChapterLevel opts,
                            writerTOCDepth         = optTOCDepth opts,
                            writerReferenceDoc     = optReferenceDoc opts,
                            writerLaTeXArgs        = optLaTeXEngineArgs opts,
                            writerSyntaxMap        = syntaxMap
                          }


#ifdef _WINDOWS
  let istty = True
#else
  istty <- queryTerminal stdOutput
#endif
  when (istty && not (isTextFormat format) && outputFile == "-") $
    E.throwIO $ PandocAppError 5 $
            "Cannot write " ++ format ++ " output to stdout.\n" ++
            "Specify an output file using the -o option."


  let transforms = case optBaseHeaderLevel opts of
                        x | x > 1 -> [headerShift (x - 1)]
                          | otherwise -> []

  let convertTabs = tabFilter (if optPreserveTabs opts || readerName == "t2t"
                                 then 0
                                 else optTabStop opts)

      readSources :: (Functor m, MonadIO m) => [FilePath] -> m String
      readSources srcs = convertTabs . intercalate "\n" <$>
                            mapM readSource srcs

  let runIO' :: PandocIO a -> IO a
      runIO' f = do
        (res, reports) <- runIOorExplode $ do
                             setVerbosity verbosity
                             x <- f
                             rs <- getLog
                             return (x, rs)
        case optLogFile opts of
             Nothing      -> return ()
             Just logfile -> B.writeFile logfile (encodeLogMessages reports)
        let isWarning msg = messageVerbosity msg == WARNING
        when (optFailIfWarnings opts && any isWarning reports) $
            E.throwIO PandocFailOnWarningError
        return res

  let sourceToDoc :: [FilePath] -> PandocIO (Pandoc, MediaBag)
      sourceToDoc sources' =
         case reader of
              StringReader r
                | optFileScope opts || readerName == "json" -> do
                    pairs <- mapM
                      (readSource >=> withMediaBag . r readerOpts) sources
                    return (mconcat (map fst pairs), mconcat (map snd pairs))
                | otherwise ->
                     readSources sources' >>= withMediaBag . r readerOpts
              ByteStringReader r -> do
                pairs <- mapM (readFile' >=>
                                 withMediaBag . r readerOpts) sources
                return (mconcat (map fst pairs), mconcat (map snd pairs))

  metadata <- if format == "jats" &&
                 lookup "csl" (optMetadata opts) == Nothing &&
                 lookup "citation-style" (optMetadata opts) == Nothing
                 then do
                   jatsCSL <- readDataFile datadir "jats.csl"
                   let jatsEncoded = makeDataURI ("application/xml", jatsCSL)
                   return $ ("csl", jatsEncoded) : optMetadata opts
                 else return $ optMetadata opts

  runIO' $ do
    (doc, media) <- sourceToDoc sources
    doc' <- (maybe return (extractMedia media) (optExtractMedia opts) >=>
              return . flip (foldr addMetadata) metadata >=>
              applyTransforms transforms >=>
              applyLuaFilters datadir (optLuaFilters opts) [format] >=>
              applyFilters datadir filters' [format]) doc

    case writer of
      -- StringWriter f -> f writerOptions doc' >>= writerFn outputFile
      ByteStringWriter f -> f writerOptions doc' >>= writeFnBinary outputFile
      StringWriter f
        | pdfOutput -> do
                -- make sure writer is latex, beamer, context, html5 or ms
                unless (laTeXOutput || conTeXtOutput || html5Output ||
                        msOutput) $
                  liftIO $ E.throwIO $ PandocAppError 47 $
                     "cannot produce pdf output with " ++ format ++ " writer"

                let pdfprog = case () of
                                _ | conTeXtOutput -> "context"
                                  | html5Output   -> "wkhtmltopdf"
                                  | html5Output   -> "wkhtmltopdf"
                                  | msOutput      -> "pdfroff"
                                  | otherwise     -> optLaTeXEngine opts
                -- check for pdf creating program
                mbPdfProg <- liftIO $ findExecutable pdfprog
                when (isNothing mbPdfProg) $ liftIO $ E.throwIO $
                       PandocPDFProgramNotFoundError pdfprog

                res <- makePDF pdfprog f writerOptions verbosity media doc'
                case res of
                     Right pdf -> writeFnBinary outputFile pdf
                     Left err' -> liftIO $ do
                       B.hPutStr stderr err'
                       B.hPut stderr $ B.pack [10]
                       E.throwIO $ PandocPDFError (UTF8.toStringLazy err')
        | otherwise -> do
                let htmlFormat = format `elem`
                      ["html","html4","html5","s5","slidy","slideous","dzslides","revealjs"]
                    selfcontain = if optSelfContained opts && htmlFormat
                                  then makeSelfContained writerOptions
                                  else return
                    handleEntities = if (htmlFormat ||
                                         format == "docbook4" ||
                                         format == "docbook5" ||
                                         format == "docbook") && optAscii opts
                                     then toEntities
                                     else id
                output <- f writerOptions doc'
                selfcontain (output ++ ['\n' | not standalone]) >>=
                    writerFn outputFile . handleEntities

type Transform = Pandoc -> Pandoc

isTextFormat :: String -> Bool
isTextFormat s = s `notElem` ["odt","docx","epub","epub3"]

externalFilter :: MonadIO m => FilePath -> [String] -> Pandoc -> m Pandoc
externalFilter f args' d = liftIO $ do
  exists <- doesFileExist f
  isExecutable <- if exists
                     then executable <$> getPermissions f
                     else return True
  let (f', args'') = if exists
                        then case map toLower (takeExtension f) of
                                  _      | isExecutable -> ("." </> f, args')
                                  ".py"  -> ("python", f:args')
                                  ".hs"  -> ("runhaskell", f:args')
                                  ".pl"  -> ("perl", f:args')
                                  ".rb"  -> ("ruby", f:args')
                                  ".php" -> ("php", f:args')
                                  ".js"  -> ("node", f:args')
                                  _      -> (f, args')
                        else (f, args')
  unless (exists && isExecutable) $ do
    mbExe <- findExecutable f'
    when (isNothing mbExe) $
      E.throwIO $ PandocFilterError f ("Could not find executable " ++ f')
  env <- getEnvironment
  let env' = Just $ ("PANDOC_VERSION", pandocVersion) : env
  (exitcode, outbs) <- E.handle filterException $
                              pipeProcess env' f' args'' $ encode d
  case exitcode of
       ExitSuccess    -> return $ either error id $ eitherDecode' outbs
       ExitFailure ec -> E.throwIO $ PandocFilterError f
                           ("Filter returned error status " ++ show ec)
 where filterException :: E.SomeException -> IO a
       filterException e = E.throwIO $ PandocFilterError f (show e)

-- | Data structure for command line options.
data Opt = Opt
    { optTabStop               :: Int     -- ^ Number of spaces per tab
    , optPreserveTabs          :: Bool    -- ^ Preserve tabs instead of converting to spaces
    , optStandalone            :: Bool    -- ^ Include header, footer
    , optReader                :: Maybe String  -- ^ Reader format
    , optWriter                :: Maybe String  -- ^ Writer format
    , optTableOfContents       :: Bool    -- ^ Include table of contents
    , optBaseHeaderLevel       :: Int     -- ^ Base header level
    , optTemplate              :: Maybe FilePath  -- ^ Custom template
    , optVariables             :: [(String,String)] -- ^ Template variables to set
    , optMetadata              :: [(String, String)] -- ^ Metadata fields to set
    , optOutputFile            :: FilePath  -- ^ Name of output file
    , optInputFiles            :: [FilePath] -- ^ Names of input files
    , optNumberSections        :: Bool    -- ^ Number sections in LaTeX
    , optNumberOffset          :: [Int]   -- ^ Starting number for sections
    , optSectionDivs           :: Bool    -- ^ Put sections in div tags in HTML
    , optIncremental           :: Bool    -- ^ Use incremental lists in Slidy/Slideous/S5
    , optSelfContained         :: Bool    -- ^ Make HTML accessible offline
    , optHtmlQTags             :: Bool    -- ^ Use <q> tags in HTML
    , optHighlightStyle        :: Maybe String -- ^ Style to use for highlighted code
    , optSyntaxDefinitions     :: [FilePath]  -- ^ xml syntax defs to load
    , optTopLevelDivision      :: TopLevelDivision -- ^ Type of the top-level divisions
    , optHTMLMathMethod        :: HTMLMathMethod -- ^ Method to print HTML math
    , optAbbreviations         :: Maybe FilePath -- ^ Path to abbrevs file
    , optReferenceDoc          :: Maybe FilePath -- ^ Path of reference doc
    , optEpubMetadata          :: Maybe FilePath   -- ^ EPUB metadata
    , optEpubFonts             :: [FilePath] -- ^ EPUB fonts to embed
    , optEpubChapterLevel      :: Int     -- ^ Header level at which to split chapters
    , optEpubCoverImage        :: Maybe FilePath -- ^ Cover image for epub
    , optTOCDepth              :: Int     -- ^ Number of levels to include in TOC
    , optDumpArgs              :: Bool    -- ^ Output command-line arguments
    , optIgnoreArgs            :: Bool    -- ^ Ignore command-line arguments
    , optVerbosity             :: Verbosity  -- ^ Verbosity of diagnostic output
    , optLogFile               :: Maybe FilePath -- ^ File to write JSON log output
    , optFailIfWarnings        :: Bool    -- ^ Fail on warnings
    , optReferenceLinks        :: Bool    -- ^ Use reference links in writing markdown, rst
    , optReferenceLocation     :: ReferenceLocation -- ^ location for footnotes and link references in markdown output
    , optDpi                   :: Int     -- ^ Dpi
    , optWrapText              :: WrapOption  -- ^ Options for wrapping text
    , optColumns               :: Int     -- ^ Line length in characters
    , optFilters               :: [FilePath] -- ^ Filters to apply
    , optLuaFilters            :: [FilePath] -- ^ Lua filters to apply
    , optEmailObfuscation      :: ObfuscationMethod
    , optIdentifierPrefix      :: String
    , optIndentedCodeClasses   :: [String] -- ^ Default classes for indented code blocks
    , optDataDir               :: Maybe FilePath
    , optCiteMethod            :: CiteMethod -- ^ Method to output cites
    , optListings              :: Bool       -- ^ Use listings package for code blocks
    , optLaTeXEngine           :: String     -- ^ Program to use for latex -> pdf
    , optLaTeXEngineArgs       :: [String]   -- ^ Flags to pass to the latex-engine
    , optSlideLevel            :: Maybe Int  -- ^ Header level that creates slides
    , optSetextHeaders         :: Bool       -- ^ Use atx headers for markdown level 1-2
    , optAscii                 :: Bool       -- ^ Use ascii characters only in html
    , optDefaultImageExtension :: String -- ^ Default image extension
    , optExtractMedia          :: Maybe FilePath -- ^ Path to extract embedded media
    , optTrackChanges          :: TrackChanges -- ^ Accept or reject MS Word track-changes.
    , optFileScope             :: Bool         -- ^ Parse input files before combining
    , optKaTeXStylesheet       :: Maybe String     -- ^ Path to stylesheet for KaTeX
    , optKaTeXJS               :: Maybe String     -- ^ Path to js file for KaTeX
    , optTitlePrefix           :: Maybe String     -- ^ Prefix for title
    , optCss                   :: [FilePath]       -- ^ CSS files to link to
    , optIncludeBeforeBody     :: [FilePath]       -- ^ Files to include before
    , optIncludeAfterBody      :: [FilePath]       -- ^ Files to include after body
    , optIncludeInHeader       :: [FilePath]       -- ^ Files to include in header
    }

-- | Defaults for command-line options.
defaultOpts :: Opt
defaultOpts = Opt
    { optTabStop               = 4
    , optPreserveTabs          = False
    , optStandalone            = False
    , optReader                = Nothing
    , optWriter                = Nothing
    , optTableOfContents       = False
    , optBaseHeaderLevel       = 1
    , optTemplate              = Nothing
    , optVariables             = []
    , optMetadata              = []
    , optOutputFile            = "-"    -- "-" means stdout
    , optInputFiles            = []
    , optNumberSections        = False
    , optNumberOffset          = [0,0,0,0,0,0]
    , optSectionDivs           = False
    , optIncremental           = False
    , optSelfContained         = False
    , optHtmlQTags             = False
    , optHighlightStyle        = Just "pygments"
    , optSyntaxDefinitions     = []
    , optTopLevelDivision      = TopLevelDefault
    , optHTMLMathMethod        = PlainMath
    , optAbbreviations         = Nothing
    , optReferenceDoc          = Nothing
    , optEpubMetadata          = Nothing
    , optEpubFonts             = []
    , optEpubChapterLevel      = 1
    , optEpubCoverImage        = Nothing
    , optTOCDepth              = 3
    , optDumpArgs              = False
    , optIgnoreArgs            = False
    , optVerbosity             = WARNING
    , optLogFile               = Nothing
    , optFailIfWarnings        = False
    , optReferenceLinks        = False
    , optReferenceLocation     = EndOfDocument
    , optDpi                   = 96
    , optWrapText              = WrapAuto
    , optColumns               = 72
    , optFilters               = []
    , optLuaFilters            = []
    , optEmailObfuscation      = NoObfuscation
    , optIdentifierPrefix      = ""
    , optIndentedCodeClasses   = []
    , optDataDir               = Nothing
    , optCiteMethod            = Citeproc
    , optListings              = False
    , optLaTeXEngine           = "pdflatex"
    , optLaTeXEngineArgs       = []
    , optSlideLevel            = Nothing
    , optSetextHeaders         = True
    , optAscii                 = False
    , optDefaultImageExtension = ""
    , optExtractMedia          = Nothing
    , optTrackChanges          = AcceptChanges
    , optFileScope             = False
    , optKaTeXStylesheet       = Nothing
    , optKaTeXJS               = Nothing
    , optTitlePrefix           = Nothing
    , optCss                   = []
    , optIncludeBeforeBody     = []
    , optIncludeAfterBody      = []
    , optIncludeInHeader       = []
    }

addMetadata :: (String, String) -> Pandoc -> Pandoc
addMetadata (k, v) (Pandoc meta bs) = Pandoc meta' bs
  where meta' = case lookupMeta k meta of
                      Nothing -> setMeta k v' meta
                      Just (MetaList xs) ->
                                 setMeta k (MetaList (xs ++ [v'])) meta
                      Just x  -> setMeta k (MetaList [x, v']) meta
        v' = readMetaValue v

readMetaValue :: String -> MetaValue
readMetaValue s = case decode (UTF8.fromString s) of
                       Just (Yaml.String t) -> MetaString $ T.unpack t
                       Just (Yaml.Bool b)   -> MetaBool b
                       _                    -> MetaString s

-- Determine default reader based on source file extensions
defaultReaderName :: String -> [FilePath] -> String
defaultReaderName fallback [] = fallback
defaultReaderName fallback (x:xs) =
  case takeExtension (map toLower x) of
    ".xhtml"    -> "html"
    ".html"     -> "html"
    ".htm"      -> "html"
    ".md"       -> "markdown"
    ".markdown" -> "markdown"
    ".tex"      -> "latex"
    ".latex"    -> "latex"
    ".ltx"      -> "latex"
    ".rst"      -> "rst"
    ".org"      -> "org"
    ".lhs"      -> "markdown+lhs"
    ".db"       -> "docbook"
    ".opml"     -> "opml"
    ".wiki"     -> "mediawiki"
    ".dokuwiki" -> "dokuwiki"
    ".textile"  -> "textile"
    ".native"   -> "native"
    ".json"     -> "json"
    ".docx"     -> "docx"
    ".t2t"      -> "t2t"
    ".epub"     -> "epub"
    ".odt"      -> "odt"
    ".pdf"      -> "pdf"  -- so we get an "unknown reader" error
    ".doc"      -> "doc"  -- so we get an "unknown reader" error
    _           -> defaultReaderName fallback xs

-- Determine default writer based on output file extension
defaultWriterName :: FilePath -> String
defaultWriterName "-" = "html" -- no output file
defaultWriterName x =
  case takeExtension (map toLower x) of
    ""          -> "markdown" -- empty extension
    ".tex"      -> "latex"
    ".latex"    -> "latex"
    ".ltx"      -> "latex"
    ".context"  -> "context"
    ".ctx"      -> "context"
    ".rtf"      -> "rtf"
    ".rst"      -> "rst"
    ".s5"       -> "s5"
    ".native"   -> "native"
    ".json"     -> "json"
    ".txt"      -> "markdown"
    ".text"     -> "markdown"
    ".md"       -> "markdown"
    ".markdown" -> "markdown"
    ".textile"  -> "textile"
    ".lhs"      -> "markdown+lhs"
    ".texi"     -> "texinfo"
    ".texinfo"  -> "texinfo"
    ".db"       -> "docbook"
    ".odt"      -> "odt"
    ".docx"     -> "docx"
    ".epub"     -> "epub"
    ".org"      -> "org"
    ".asciidoc" -> "asciidoc"
    ".adoc"     -> "asciidoc"
    ".pdf"      -> "latex"
    ".fb2"      -> "fb2"
    ".opml"     -> "opml"
    ".icml"     -> "icml"
    ".tei.xml"  -> "tei"
    ".tei"      -> "tei"
    ".ms"       -> "ms"
    ".roff"     -> "ms"
    ['.',y]     | y `elem` ['1'..'9'] -> "man"
    _           -> "html"

-- Transformations of a Pandoc document post-parsing:

extractMedia :: MonadIO m => MediaBag -> FilePath -> Pandoc -> m Pandoc
extractMedia media dir d =
  case [fp | (fp, _, _) <- mediaDirectory media] of
        []  -> return d
        fps -> do
          extractMediaBag True dir media
          return $ walk (adjustImagePath dir fps) d

adjustImagePath :: FilePath -> [FilePath] -> Inline -> Inline
adjustImagePath dir paths (Image attr lab (src, tit))
   | src `elem` paths = Image attr lab (dir ++ "/" ++ src, tit)
adjustImagePath _ _ x = x

applyTransforms :: Monad m => [Transform] -> Pandoc -> m Pandoc
applyTransforms transforms d = return $ foldr ($) d transforms

  -- First we check to see if a filter is found.  If not, and if it's
  -- not an absolute path, we check to see whether it's in `userdir/filters`.
  -- If not, we leave it unchanged.
expandFilterPath :: MonadIO m => Maybe FilePath -> FilePath -> m FilePath
expandFilterPath mbDatadir fp = liftIO $ do
  fpExists <- doesFileExist fp
  if fpExists
     then return fp
     else case mbDatadir of
               Just datadir | isRelative fp -> do
                 let filterPath = datadir </> "filters" </> fp
                 filterPathExists <- doesFileExist filterPath
                 if filterPathExists
                    then return filterPath
                    else return fp
               _ -> return fp

applyLuaFilters :: MonadIO m
                => Maybe FilePath -> [FilePath] -> [String] -> Pandoc -> m Pandoc
applyLuaFilters mbDatadir filters args d = do
  expandedFilters <- mapM (expandFilterPath mbDatadir) filters
  foldrM ($) d $ map (flip runLuaFilter args) expandedFilters

applyFilters :: MonadIO m
             => Maybe FilePath -> [FilePath] -> [String] -> Pandoc -> m Pandoc
applyFilters mbDatadir filters args d = do
  expandedFilters <- mapM (expandFilterPath mbDatadir) filters
  foldrM ($) d $ map (flip externalFilter args) expandedFilters

readSource :: MonadIO m => FilePath -> m String
readSource "-" = liftIO UTF8.getContents
readSource src = case parseURI src of
                      Just u | uriScheme u `elem` ["http:","https:"] ->
                                 readURI src
                             | uriScheme u == "file:" ->
                                 liftIO $ UTF8.readFile (uriPath u)
                      _       -> liftIO $ UTF8.readFile src

readURI :: MonadIO m => FilePath -> m String
readURI src = liftIO $ (UTF8.toString . fst) <$> openURL src

readFile' :: MonadIO m => FilePath -> m B.ByteString
readFile' "-" = liftIO B.getContents
readFile' f   = liftIO $ B.readFile f

writeFnBinary :: MonadIO m => FilePath -> B.ByteString -> m ()
writeFnBinary "-" = liftIO . B.putStr
writeFnBinary f   = liftIO . B.writeFile (UTF8.encodePath f)

writerFn :: MonadIO m => FilePath -> String -> m ()
writerFn "-" = liftIO . UTF8.putStr
writerFn f   = liftIO . UTF8.writeFile f

lookupHighlightStyle :: Maybe String -> IO (Maybe Style)
lookupHighlightStyle Nothing = return Nothing
lookupHighlightStyle (Just s)
  | takeExtension s == ".theme" = -- attempt to load KDE theme
    do contents <- B.readFile s
       case parseTheme contents of
            Left _    -> E.throwIO $ PandocAppError 69 $
                           "Could not read highlighting theme " ++ s
            Right sty -> return (Just sty)
  | otherwise =
  case lookup (map toLower s) highlightingStyles of
       Just sty -> return (Just sty)
       Nothing  -> E.throwIO $ PandocAppError 68 $
                      "Unknown highlight-style " ++ s

-- | A list of functions, each transforming the options data structure
--   in response to a command-line option.
options :: [OptDescr (Opt -> IO Opt)]
options =
    [ Option "fr" ["from","read"]
                 (ReqArg
                  (\arg opt -> return opt { optReader = Just arg })
                  "FORMAT")
                 ""

    , Option "tw" ["to","write"]
                 (ReqArg
                  (\arg opt -> return opt { optWriter = Just arg })
                  "FORMAT")
                 ""

    , Option "o" ["output"]
                 (ReqArg
                  (\arg opt -> return opt { optOutputFile = arg })
                  "FILE")
                 "" -- "Name of output file"

    , Option "" ["data-dir"]
                 (ReqArg
                  (\arg opt -> return opt { optDataDir = Just arg })
                 "DIRECTORY") -- "Directory containing pandoc data files."
                ""

    , Option "" ["base-header-level"]
                 (ReqArg
                  (\arg opt ->
                      case safeRead arg of
                           Just t | t > 0 && t < 6 ->
                               return opt{ optBaseHeaderLevel = t }
                           _              -> E.throwIO $ PandocAppError 19
                                               "base-header-level must be 1-5")
                  "NUMBER")
                 "" -- "Headers base level"

     , Option "" ["indented-code-classes"]
                  (ReqArg
                   (\arg opt -> return opt { optIndentedCodeClasses = words $
                                             map (\c -> if c == ',' then ' ' else c) arg })
                   "STRING")
                  "" -- "Classes (whitespace- or comma-separated) to use for indented code-blocks"

    , Option "F" ["filter"]
                 (ReqArg
                  (\arg opt -> return opt { optFilters = arg : optFilters opt })
                  "PROGRAM")
                 "" -- "External JSON filter"

    , Option "" ["lua-filter"]
                 (ReqArg
                  (\arg opt -> return opt { optLuaFilters = arg : optLuaFilters opt })
                  "SCRIPTPATH")
                 "" -- "Lua filter"

    , Option "p" ["preserve-tabs"]
                 (NoArg
                  (\opt -> return opt { optPreserveTabs = True }))
                 "" -- "Preserve tabs instead of converting to spaces"

    , Option "" ["tab-stop"]
                 (ReqArg
                  (\arg opt ->
                      case safeRead arg of
                           Just t | t > 0 -> return opt { optTabStop = t }
                           _              -> E.throwIO $ PandocAppError 31
                                  "tab-stop must be a number greater than 0")
                  "NUMBER")
                 "" -- "Tab stop (default 4)"

    , Option "" ["track-changes"]
                 (ReqArg
                  (\arg opt -> do
                     action <- case arg of
                            "accept" -> return AcceptChanges
                            "reject" -> return RejectChanges
                            "all"    -> return AllChanges
                            _        -> E.throwIO $ PandocAppError 6
                               ("Unknown option for track-changes: " ++ arg)
                     return opt { optTrackChanges = action })
                  "accept|reject|all")
                 "" -- "Accepting or reject MS Word track-changes.""

    , Option "" ["file-scope"]
                 (NoArg
                  (\opt -> return opt { optFileScope = True }))
                 "" -- "Parse input files before combining"

    , Option "" ["extract-media"]
                 (ReqArg
                  (\arg opt ->
                    return opt { optExtractMedia = Just arg })
                  "PATH")
                 "" -- "Directory to which to extract embedded media"

    , Option "s" ["standalone"]
                 (NoArg
                  (\opt -> return opt { optStandalone = True }))
                 "" -- "Include needed header and footer on output"

    , Option "" ["template"]
                 (ReqArg
                  (\arg opt ->
                     return opt{ optTemplate = Just arg,
                                 optStandalone = True })
                  "FILE")
                 "" -- "Use custom template"

    , Option "M" ["metadata"]
                 (ReqArg
                  (\arg opt -> do
                     let (key, val) = splitField arg
                     return opt{ optMetadata = (key, val) : optMetadata opt })
                  "KEY[:VALUE]")
                 ""

    , Option "V" ["variable"]
                 (ReqArg
                  (\arg opt -> do
                     let (key, val) = splitField arg
                     return opt{ optVariables = (key, val) : optVariables opt })
                  "KEY[:VALUE]")
                 ""

    , Option "D" ["print-default-template"]
                 (ReqArg
                  (\arg _ -> do
                     templ <- getDefaultTemplate Nothing arg
                     case templ of
                          Right t -> UTF8.hPutStr stdout t
                          Left e  -> error $ show e
                     exitSuccess)
                  "FORMAT")
                 "" -- "Print default template for FORMAT"

    , Option "" ["print-default-data-file"]
                 (ReqArg
                  (\arg _ -> do
                     readDataFile Nothing arg >>= BS.hPutStr stdout
                     exitSuccess)
                  "FILE")
                  "" -- "Print default data file"

    , Option "" ["dpi"]
                 (ReqArg
                  (\arg opt ->
                    case safeRead arg of
                         Just t | t > 0 -> return opt { optDpi = t }
                         _              -> E.throwIO $ PandocAppError 31
                                        "dpi must be a number greater than 0")
                  "NUMBER")
                 "" -- "Dpi (default 96)"

    , Option "" ["wrap"]
                 (ReqArg
                  (\arg opt ->
                    case safeRead ("Wrap" ++ uppercaseFirstLetter arg) of
                          Just o   -> return opt { optWrapText = o }
                          Nothing  -> E.throwIO $ PandocAppError 77
                                     "--wrap must be auto, none, or preserve")
                 "auto|none|preserve")
                 "" -- "Option for wrapping text in output"

    , Option "" ["columns"]
                 (ReqArg
                  (\arg opt ->
                      case safeRead arg of
                           Just t | t > 0 -> return opt { optColumns = t }
                           _              -> E.throwIO $ PandocAppError 33
                                   "columns must be a number greater than 0")
                 "NUMBER")
                 "" -- "Length of line in characters"

    , Option "" ["toc", "table-of-contents"]
                (NoArg
                 (\opt -> return opt { optTableOfContents = True }))
               "" -- "Include table of contents"

    , Option "" ["toc-depth"]
                 (ReqArg
                  (\arg opt ->
                      case safeRead arg of
                           Just t | t >= 1 && t <= 6 ->
                                    return opt { optTOCDepth = t }
                           _      -> E.throwIO $ PandocAppError 57
                                    "TOC level must be a number between 1 and 6")
                 "NUMBER")
                 "" -- "Number of levels to include in TOC"

    , Option "" ["no-highlight"]
                (NoArg
                 (\opt -> return opt { optHighlightStyle = Nothing }))
                 "" -- "Don't highlight source code"

    , Option "" ["highlight-style"]
                (ReqArg
                 (\arg opt -> return opt{ optHighlightStyle = Just arg })
                 "STYLE")
                 "" -- "Style for highlighted code"

    , Option "" ["syntax-definition"]
                (ReqArg
                 (\arg opt -> return opt{ optSyntaxDefinitions = arg :
                                             optSyntaxDefinitions opt })
                 "FILE")
                "" -- "Syntax definition (xml) file"

    , Option "H" ["include-in-header"]
                 (ReqArg
                  (\arg opt -> return opt{ optIncludeInHeader =
                                              arg : optIncludeInHeader opt,
                                            optStandalone = True })
                  "FILE")
                 "" -- "File to include at end of header (implies -s)"

    , Option "B" ["include-before-body"]
                 (ReqArg
                  (\arg opt -> return opt{ optIncludeBeforeBody =
                                              arg : optIncludeBeforeBody opt,
                                           optStandalone = True })
                  "FILE")
                 "" -- "File to include before document body"

    , Option "A" ["include-after-body"]
                 (ReqArg
                  (\arg opt -> return opt{ optIncludeAfterBody =
                                              arg : optIncludeAfterBody opt,
                                           optStandalone = True })
                  "FILE")
                 "" -- "File to include after document body"

    , Option "" ["self-contained"]
                 (NoArg
                  (\opt -> return opt { optSelfContained = True,
                                        optStandalone = True }))
                 "" -- "Make slide shows include all the needed js and css"

    , Option "" ["html-q-tags"]
                 (NoArg
                  (\opt ->
                     return opt { optHtmlQTags = True }))
                 "" -- "Use <q> tags for quotes in HTML"

    , Option "" ["ascii"]
                 (NoArg
                  (\opt -> return opt { optAscii = True }))
                 ""  -- "Use ascii characters only in HTML output"

    , Option "" ["reference-links"]
                 (NoArg
                  (\opt -> return opt { optReferenceLinks = True } ))
                 "" -- "Use reference links in parsing HTML"

    , Option "" ["reference-location"]
                 (ReqArg
                  (\arg opt -> do
                     action <- case arg of
                            "block"    -> return EndOfBlock
                            "section"  -> return EndOfSection
                            "document" -> return EndOfDocument
                            _        -> E.throwIO $ PandocAppError 6
                               ("Unknown option for reference-location: " ++ arg)
                     return opt { optReferenceLocation = action })
                  "block|section|document")
                 "" -- "Accepting or reject MS Word track-changes.""

    , Option "" ["atx-headers"]
                 (NoArg
                  (\opt -> return opt { optSetextHeaders = False } ))
                 "" -- "Use atx-style headers for markdown"

    , Option "" ["top-level-division"]
                 (ReqArg
                  (\arg opt -> do
                      let tldName = "TopLevel" ++ uppercaseFirstLetter arg
                      case safeRead tldName of
                        Just tlDiv -> return opt { optTopLevelDivision = tlDiv }
                        _       -> E.throwIO $ PandocAppError 76
                                     ("Top-level division must be " ++
                                      "section,  chapter, part, or default"))
                   "section|chapter|part")
                 "" -- "Use top-level division type in LaTeX, ConTeXt, DocBook"

    , Option "N" ["number-sections"]
                 (NoArg
                  (\opt -> return opt { optNumberSections = True }))
                 "" -- "Number sections in LaTeX"

    , Option "" ["number-offset"]
                 (ReqArg
                  (\arg opt ->
                      case safeRead ('[':arg ++ "]") of
                           Just ns -> return opt { optNumberOffset = ns,
                                                   optNumberSections = True }
                           _      -> E.throwIO $ PandocAppError 57
                                       "could not parse number-offset")
                 "NUMBERS")
                 "" -- "Starting number for sections, subsections, etc."

    , Option "" ["listings"]
                 (NoArg
                  (\opt -> return opt { optListings = True }))
                 "" -- "Use listings package for LaTeX code blocks"

    , Option "i" ["incremental"]
                 (NoArg
                  (\opt -> return opt { optIncremental = True }))
                 "" -- "Make list items display incrementally in Slidy/Slideous/S5"

    , Option "" ["slide-level"]
                 (ReqArg
                  (\arg opt ->
                      case safeRead arg of
                           Just t | t >= 1 && t <= 6 ->
                                    return opt { optSlideLevel = Just t }
                           _      -> E.throwIO $ PandocAppError 39
                                    "slide level must be a number between 1 and 6")
                 "NUMBER")
                 "" -- "Force header level for slides"

    , Option "" ["section-divs"]
                 (NoArg
                  (\opt -> return opt { optSectionDivs = True }))
                 "" -- "Put sections in div tags in HTML"

    , Option "" ["default-image-extension"]
                 (ReqArg
                  (\arg opt -> return opt { optDefaultImageExtension = arg })
                   "extension")
                  "" -- "Default extension for extensionless images"

    , Option "" ["email-obfuscation"]
                 (ReqArg
                  (\arg opt -> do
                     method <- case arg of
                            "references" -> return ReferenceObfuscation
                            "javascript" -> return JavascriptObfuscation
                            "none"       -> return NoObfuscation
                            _            -> E.throwIO $ PandocAppError 6
                               ("Unknown obfuscation method: " ++ arg)
                     return opt { optEmailObfuscation = method })
                  "none|javascript|references")
                 "" -- "Method for obfuscating email in HTML"

     , Option "" ["id-prefix"]
                  (ReqArg
                   (\arg opt -> return opt { optIdentifierPrefix = arg })
                   "STRING")
                  "" -- "Prefix to add to automatically generated HTML identifiers"

    , Option "T" ["title-prefix"]
                 (ReqArg
                  (\arg opt -> do
                    let newvars = ("title-prefix", arg) : optVariables opt
                    return opt { optVariables = newvars,
                                 optStandalone = True })
                  "STRING")
                 "" -- "String to prefix to HTML window title"

    , Option "c" ["css"]
                 (ReqArg
                  (\arg opt -> return opt{ optCss = arg : optCss opt })
                  -- add new link to end, so it is included in proper order
                  "URL")
                 "" -- "Link to CSS style sheet"

    , Option "" ["reference-doc"]
                 (ReqArg
                  (\arg opt ->
                    return opt { optReferenceDoc = Just arg })
                  "FILE")
                 "" -- "Path of custom reference doc"

    , Option "" ["epub-cover-image"]
                 (ReqArg
                  (\arg opt ->
                     return opt { optVariables =
                                 ("epub-cover-image", arg) : optVariables opt })
                  "FILE")
                 "" -- "Path of epub cover image"

    , Option "" ["epub-metadata"]
                 (ReqArg
                  (\arg opt -> return opt { optEpubMetadata = Just arg })
                  "FILE")
                 "" -- "Path of epub metadata file"

    , Option "" ["epub-embed-font"]
                 (ReqArg
                  (\arg opt ->
                     return opt{ optEpubFonts = arg : optEpubFonts opt })
                  "FILE")
                 "" -- "Directory of fonts to embed"

    , Option "" ["epub-chapter-level"]
                 (ReqArg
                  (\arg opt ->
                      case safeRead arg of
                           Just t | t >= 1 && t <= 6 ->
                                    return opt { optEpubChapterLevel = t }
                           _      -> E.throwIO $ PandocAppError 59
                                    "chapter level must be a number between 1 and 6")
                 "NUMBER")
                 "" -- "Header level at which to split chapters in EPUB"

    , Option "" ["latex-engine"]
                 (ReqArg
                  (\arg opt -> do
                     let b = takeBaseName arg
                     if b `elem` ["pdflatex", "lualatex", "xelatex"]
                        then return opt { optLaTeXEngine = arg }
                        else E.throwIO $ PandocAppError 45 "latex-engine must be pdflatex, lualatex, or xelatex.")
                  "PROGRAM")
                 "" -- "Name of latex program to use in generating PDF"

    , Option "" ["latex-engine-opt"]
                 (ReqArg
                  (\arg opt -> do
                      let oldArgs = optLaTeXEngineArgs opt
                      return opt { optLaTeXEngineArgs = arg : oldArgs })
                  "STRING")
                 "" -- "Flags to pass to the LaTeX engine, all instances of this option are accumulated and used"

    , Option "" ["bibliography"]
                 (ReqArg
                  (\arg opt -> return opt{ optMetadata =
                                 ("bibliography", arg) : optMetadata opt })
                   "FILE")
                 ""

     , Option "" ["csl"]
                 (ReqArg
                  (\arg opt ->
                     return opt{ optMetadata =
                                   ("csl", arg) : optMetadata opt })
                   "FILE")
                 ""

     , Option "" ["citation-abbreviations"]
                 (ReqArg
                  (\arg opt ->
                     return opt{ optMetadata =
                              ("citation-abbreviations", arg): optMetadata opt })
                   "FILE")
                 ""

    , Option "" ["natbib"]
                 (NoArg
                  (\opt -> return opt { optCiteMethod = Natbib }))
                 "" -- "Use natbib cite commands in LaTeX output"

    , Option "" ["biblatex"]
                 (NoArg
                  (\opt -> return opt { optCiteMethod = Biblatex }))
                 "" -- "Use biblatex cite commands in LaTeX output"

    , Option "m" ["latexmathml", "asciimathml"]
                 (OptArg
                  (\arg opt ->
                      return opt { optHTMLMathMethod = LaTeXMathML arg })
                  "URL")
                 "" -- "Use LaTeXMathML script in html output"

    , Option "" ["mathml"]
                 (NoArg
                  (\opt ->
                      return opt { optHTMLMathMethod = MathML }))
                 "" -- "Use mathml for HTML math"

    , Option "" ["mimetex"]
                 (OptArg
                  (\arg opt -> do
                      let url' = case arg of
                                      Just u  -> u ++ "?"
                                      Nothing -> "/cgi-bin/mimetex.cgi?"
                      return opt { optHTMLMathMethod = WebTeX url' })
                  "URL")
                 "" -- "Use mimetex for HTML math"

    , Option "" ["webtex"]
                 (OptArg
                  (\arg opt -> do
                      let url' = fromMaybe "https://latex.codecogs.com/png.latex?" arg
                      return opt { optHTMLMathMethod = WebTeX url' })
                  "URL")
                 "" -- "Use web service for HTML math"

    , Option "" ["jsmath"]
                 (OptArg
                  (\arg opt -> return opt { optHTMLMathMethod = JsMath arg})
                  "URL")
                 "" -- "Use jsMath for HTML math"

    , Option "" ["mathjax"]
                 (OptArg
                  (\arg opt -> do
                      let url' = fromMaybe "https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.0/MathJax.js?config=TeX-AMS_CHTML-full" arg
                      return opt { optHTMLMathMethod = MathJax url'})
                  "URL")
                 "" -- "Use MathJax for HTML math"
    , Option "" ["katex"]
                 (OptArg
                  (\arg opt ->
                      return opt
                        { optKaTeXJS =
                           arg <|> Just "https://cdnjs.cloudflare.com/ajax/libs/KaTeX/0.6.0/katex.min.js"})
                  "URL")
                  "" -- Use KaTeX for HTML Math

    , Option "" ["katex-stylesheet"]
                 (ReqArg
                  (\arg opt ->
                      return opt { optKaTeXStylesheet = Just arg })
                 "URL")
                 "" -- Set the KaTeX Stylesheet location

    , Option "" ["gladtex"]
                 (NoArg
                  (\opt -> return opt { optHTMLMathMethod = GladTeX }))
                 "" -- "Use gladtex for HTML math"

    , Option "" ["abbreviations"]
                (ReqArg
                 (\arg opt -> return opt { optAbbreviations = Just arg })
                "FILE")
                "" -- "Specify file for custom abbreviations"

    , Option "" ["trace"]
                 (NoArg
                  (\opt -> return opt { optVerbosity = DEBUG }))
                 "" -- "Turn on diagnostic tracing in readers."

    , Option "" ["dump-args"]
                 (NoArg
                  (\opt -> return opt { optDumpArgs = True }))
                 "" -- "Print output filename and arguments to stdout."

    , Option "" ["ignore-args"]
                 (NoArg
                  (\opt -> return opt { optIgnoreArgs = True }))
                 "" -- "Ignore command-line arguments."

    , Option "" ["verbose"]
                 (NoArg
                  (\opt -> return opt { optVerbosity = INFO }))
                 "" -- "Verbose diagnostic output."

    , Option "" ["quiet"]
                 (NoArg
                  (\opt -> return opt { optVerbosity = ERROR }))
                 "" -- "Suppress warnings."

    , Option "" ["fail-if-warnings"]
                 (NoArg
                  (\opt -> return opt { optFailIfWarnings = True }))
                 "" -- "Exit with error status if there were  warnings."

    , Option "" ["log"]
                 (ReqArg
                  (\arg opt -> return opt{ optLogFile = Just arg })
                "FILE")
                "" -- "Log messages in JSON format to this file."

    , Option "" ["bash-completion"]
                 (NoArg
                  (\_ -> do
                     ddir <- getDataDir
                     tpl <- readDataFileUTF8 Nothing "bash_completion.tpl"
                     let optnames (Option shorts longs _ _) =
                           map (\c -> ['-',c]) shorts ++
                           map ("--" ++) longs
                     let allopts = unwords (concatMap optnames options)
                     UTF8.hPutStrLn stdout $ printf tpl allopts
                         (unwords readers'names)
                         (unwords writers'names)
                         (unwords $ map fst highlightingStyles)
                         ddir
                     exitSuccess ))
                 "" -- "Print bash completion script"

    , Option "" ["list-input-formats"]
                 (NoArg
                  (\_ -> do
                     mapM_ (UTF8.hPutStrLn stdout) readers'names
                     exitSuccess ))
                 ""

    , Option "" ["list-output-formats"]
                 (NoArg
                  (\_ -> do
                     mapM_ (UTF8.hPutStrLn stdout) writers'names
                     exitSuccess ))
                 ""

    , Option "" ["list-extensions"]
                 (NoArg
                  (\_ -> do
                     let showExt x = drop 4 (show x) ++
                                       if extensionEnabled x pandocExtensions
                                          then " +"
                                          else " -"
                     mapM_ (UTF8.hPutStrLn stdout . showExt)
                               ([minBound..maxBound] :: [Extension])
                     exitSuccess ))
                 ""

    , Option "" ["list-highlight-languages"]
                 (NoArg
                  (\_ -> do
                     let langs = [ T.unpack (T.toLower (sShortname s))
                                 | s <- M.elems defaultSyntaxMap
                                 , sShortname s `notElem`
                                    [T.pack "Alert", T.pack "Alert_indent"]
                                 ]
                     mapM_ (UTF8.hPutStrLn stdout) langs
                     exitSuccess ))
                 ""

    , Option "" ["list-highlight-styles"]
                 (NoArg
                  (\_ -> do
                     mapM_ (UTF8.hPutStrLn stdout . fst) highlightingStyles
                     exitSuccess ))
                 ""

    , Option "v" ["version"]
                 (NoArg
                  (\_ -> do
                     prg <- getProgName
                     defaultDatadir <- E.catch
                            (getAppUserDataDirectory "pandoc")
                            (\e -> let _ = (e :: E.SomeException)
                                   in  return "")
                     UTF8.hPutStrLn stdout (prg ++ " " ++ pandocVersion ++
                       compileInfo ++ "\nDefault user data directory: " ++
                       defaultDatadir ++ copyrightMessage)
                     exitSuccess ))
                 "" -- "Print version"

    , Option "h" ["help"]
                 (NoArg
                  (\_ -> do
                     prg <- getProgName
                     UTF8.hPutStr stdout (usageMessage prg options)
                     exitSuccess ))
                 "" -- "Show help"

    ]

-- Returns usage message
usageMessage :: String -> [OptDescr (Opt -> IO Opt)] -> String
usageMessage programName = usageInfo (programName ++ " [OPTIONS] [FILES]")

copyrightMessage :: String
copyrightMessage = intercalate "\n" [
  "",
  "Copyright (C) 2006-2017 John MacFarlane",
  "Web:  http://pandoc.org",
  "This is free software; see the source for copying conditions.",
  "There is no warranty, not even for merchantability or fitness",
  "for a particular purpose." ]

compileInfo :: String
compileInfo =
  "\nCompiled with pandoc-types " ++ VERSION_pandoc_types ++ ", texmath " ++
  VERSION_texmath ++ ", skylighting " ++ VERSION_skylighting

handleUnrecognizedOption :: String -> [String] -> [String]
handleUnrecognizedOption "--smart" =
  (("--smart/-S has been removed.  Use +smart or -smart extension instead.\n" ++
    "For example: pandoc -f markdown+smart -t markdown-smart.") :)
handleUnrecognizedOption "-S" = handleUnrecognizedOption "--smart"
handleUnrecognizedOption "--old-dashes" =
  ("--old-dashes has been removed.  Use +old_dashes extension instead." :)
handleUnrecognizedOption "--no-wrap" =
  ("--no-wrap has been removed.  Use --wrap=none instead." :)
handleUnrecognizedOption "--chapters" =
  ("--chapters has been removed. Use --top-level-division=chapter instead." :)
handleUnrecognizedOption "--reference-docx" =
  ("--reference-docx has been removed. Use --reference-doc instead." :)
handleUnrecognizedOption "--reference-odt" =
  ("--reference-odt has been removed. Use --reference-doc instead." :)
handleUnrecognizedOption "--parse-raw" =
  ("--parse-raw/-R has been removed. Use +raw_html or +raw_tex extension.\n" :)
handleUnrecognizedOption "--epub-stylesheet" =
  ("--epub-stylesheet has been removed. Use --css instead.\n" :)
handleUnrecognizedOption "-R" = handleUnrecognizedOption "--parse-raw"
handleUnrecognizedOption x =
  (("Unknown option " ++ x ++ ".") :)

uppercaseFirstLetter :: String -> String
uppercaseFirstLetter (c:cs) = toUpper c : cs
uppercaseFirstLetter []     = []

readers'names :: [String]
readers'names = sort (map fst (readers :: [(String, Reader PandocIO)]))

writers'names :: [String]
writers'names = sort (map fst (writers :: [(String, Writer PandocIO)]))

splitField :: String -> (String, String)
splitField s =
  case break (`elem` ":=") s of
       (k,_:v) -> (k,v)
       (k,[])  -> (k,"true")