App: extract output settings into module

4 files changed, 348 insertions, 204 deletions

diff --git a/pandoc.cabal b/pandoc.cabal
index 33087716c..01e7b1153 100644
--- a/pandoc.cabal
+++ b/pandoc.cabal
@@ -515,6 +515,7 @@ library
                    Text.Pandoc.BCP47,
                    Text.Pandoc.Class
   other-modules:   Text.Pandoc.App.CommandLineOptions,
+                   Text.Pandoc.App.OutputSettings,
                    Text.Pandoc.Filter.JSON,
                    Text.Pandoc.Filter.Lua,
                    Text.Pandoc.Filter.Path,
diff --git a/src/Text/Pandoc/App.hs b/src/Text/Pandoc/App.hs
index cf4c9173d..173c60a56 100644
--- a/src/Text/Pandoc/App.hs
+++ b/src/Text/Pandoc/App.hs
@@ -1,7 +1,6 @@
 {-# LANGUAGE NoImplicitPrelude #-}
 {-# LANGUAGE CPP                 #-}
 {-# LANGUAGE ScopedTypeVariables #-}
-{-# LANGUAGE TupleSections       #-}
 {-
 Copyright (C) 2006-2018 John MacFarlane <jgm@berkeley.edu>
 
@@ -44,12 +43,10 @@ module Text.Pandoc.App (
 import Prelude
 import qualified Control.Exception as E
 import Control.Monad
-import Control.Monad.Except (catchError, throwError)
 import Control.Monad.Trans
 import qualified Data.ByteString as BS
 import qualified Data.ByteString.Lazy as B
 import Data.Char (toLower)
-import Data.List (find, isPrefixOf, isSuffixOf)
 import Data.Maybe (fromMaybe, isJust, isNothing)
 import qualified Data.Set as Set
 import Data.Text (Text)
@@ -59,8 +56,6 @@ import qualified Data.Text.Lazy.Encoding as TE
 import qualified Data.Text.Encoding.Error as TE
 import qualified Data.YAML as YAML
 import Network.URI (URI (..), parseURI)
-import Skylighting (defaultSyntaxMap)
-import Skylighting.Parser (addSyntaxDefinition, parseSyntaxDefinition)
 import System.Directory (getAppUserDataDirectory)
 import System.Exit (exitSuccess)
 import System.FilePath
@@ -68,7 +63,8 @@ import System.IO (nativeNewline, stdout)
 import qualified System.IO as IO (Newline (..))
 import Text.Pandoc
 import Text.Pandoc.App.CommandLineOptions (Opt (..), LineEnding (..),
-        defaultOpts, engines, parseOptions, options)
+        defaultOpts, parseOptions, options)
+import Text.Pandoc.App.OutputSettings (OutputSettings (..), optToOutputSettings)
 import Text.Pandoc.BCP47 (Lang (..), parseBCP47)
 import Text.Pandoc.Builder (setMeta, deleteMeta)
 import Text.Pandoc.Filter (Filter (JSONFilter, LuaFilter), applyFilters)
@@ -83,41 +79,6 @@ import System.Posix.IO (stdOutput)
 import System.Posix.Terminal (queryTerminal)
 #endif
 
-pdfIsNoWriterErrorMsg :: String
-pdfIsNoWriterErrorMsg =
-  "To create a pdf using pandoc, use " ++
-  "-t latex|beamer|context|ms|html5" ++
-  "\nand specify an output file with " ++
-  ".pdf extension (-o filename.pdf)."
-
-pdfWriterAndProg :: Maybe String              -- ^ user-specified writer name
-                 -> Maybe String              -- ^ user-specified pdf-engine
-                 -> IO (String, Maybe String) -- ^ IO (writerName, maybePdfEngineProg)
-pdfWriterAndProg mWriter mEngine = do
-  let panErr msg = liftIO $ E.throwIO $ PandocAppError msg
-  case go mWriter mEngine of
-      Right (writ, prog) -> return (writ, Just prog)
-      Left err           -> panErr err
-    where
-      go Nothing Nothing       = Right ("latex", "pdflatex")
-      go (Just writer) Nothing = (writer,) <$> engineForWriter writer
-      go Nothing (Just engine) = (,engine) <$> writerForEngine (takeBaseName engine)
-      go (Just writer) (Just engine) =
-           case find (== (baseWriterName writer, takeBaseName engine)) engines of
-                Just _  -> Right (writer, engine)
-                Nothing -> Left $ "pdf-engine " ++ engine ++
-                           " is not compatible with output format " ++ writer
-
-      writerForEngine eng = case [f | (f,e) <- engines, e == eng] of
-                                 fmt : _ -> Right fmt
-                                 []      -> Left $
-                                   "pdf-engine " ++ eng ++ " not known"
-
-      engineForWriter "pdf" = Left pdfIsNoWriterErrorMsg
-      engineForWriter w = case [e |  (f,e) <- engines, f == baseWriterName w] of
-                                eng : _ -> Right eng
-                                []      -> Left $
-                                   "cannot produce pdf output from " ++ w
 
 convertWithOpts :: Opt -> IO ()
 convertWithOpts opts = do
@@ -130,10 +91,6 @@ convertWithOpts opts = do
        mapM_ (UTF8.hPutStrLn stdout) (optInputFiles opts)
        exitSuccess
 
-  epubMetadata <- case optEpubMetadata opts of
-                         Nothing -> return Nothing
-                         Just fp -> Just <$> UTF8.readFile fp
-
   let isPandocCiteproc (JSONFilter f) = takeBaseName f == "pandoc-citeproc"
       isPandocCiteproc _              = False
   -- --bibliography implies -F pandoc-citeproc for backwards compatibility:
@@ -165,30 +122,6 @@ convertWithOpts opts = do
 
   let pdfOutput = map toLower (takeExtension outputFile) == ".pdf"
 
-  (writerName, maybePdfProg) <-
-    if pdfOutput
-       then pdfWriterAndProg (optWriter opts) (optPdfEngine opts)
-       else case optWriter opts of
-              Nothing  ->
-                return (formatFromFilePaths "html" [outputFile], Nothing)
-              Just f   -> return (f, Nothing)
-
-  let format = map toLower $ baseWriterName
-                 $ takeFileName writerName  -- in case path to lua script
-
-  -- disabling the custom writer for now
-  (writer, writerExts) <-
-            if ".lua" `isSuffixOf` format
-               then return (TextWriter
-                       (\o d -> writeCustom writerName o d)
-                               :: Writer PandocIO, mempty)
-               else case getWriter (map toLower writerName) of
-                         Left e  -> E.throwIO $ PandocAppError $
-                           if format == "pdf"
-                              then e ++ "\n" ++ pdfIsNoWriterErrorMsg
-                              else e
-                         Right (w, es) -> return (w :: Writer PandocIO, es)
-
   -- TODO: we have to get the input and the output into the state for
   -- the sake of the text2tags reader.
   (reader, readerExts) <-
@@ -202,34 +135,6 @@ convertWithOpts opts = do
                                      "\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
-  let addStringAsVariable varname s vars = return $ (varname, s) : vars
-
-  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)
-
-  -- We don't want to send output to the terminal if the user
-  -- does 'pandoc -t docx input.txt'; though we allow them to
-  -- force this with '-o -'.  On posix systems, we detect
-  -- when stdout is being piped and allow output to stdout
-  -- in that case, but on Windows we can't.
-#ifdef _WINDOWS
-  let istty = True
-#else
-  istty <- queryTerminal stdOutput
-#endif
-  when (not (isTextFormat format) && istty && isNothing ( optOutputFile opts)) $
-    E.throwIO $ PandocAppError $
-            "Cannot write " ++ format ++ " output to terminal.\n" ++
-            "Specify an output file using the -o option, or " ++
-            "use '-o -' to force output to stdout."
-
   let convertTabs = tabFilter (if optPreserveTabs opts ||
                                     readerName == "t2t" ||
                                     readerName == "man"
@@ -261,80 +166,41 @@ convertWithOpts opts = do
                  LF     -> IO.LF
                  Native -> nativeNewline
 
-  -- 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
-
-  let addContentsAsVariable varname fp vars = do
-             s <- UTF8.toString <$> readFileStrict fp
-             return $ (varname, s) : vars
-
   runIO' $ do
     setUserDataDir datadir
     setInputFiles (optInputFiles opts)
     setOutputFile (optOutputFile opts)
 
-    variables <-
-        withList (addStringAsVariable "sourcefile")
-                 (reverse $ optInputFiles opts)
-                 (("outputfile", fromMaybe "-" (optOutputFile opts))
-                  : optVariables 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 ->  if format == "dzslides"
-                      then do
-                          dztempl <- UTF8.toString <$> readDataFile
-                                       ("dzslides" </> "template.html")
-                          let dzline = "<!-- {{{{ dzslides core"
-                          let dzcore = unlines
-                                     $ dropWhile (not . (dzline `isPrefixOf`))
-                                     $ lines dztempl
-                          return $ ("dzslides-core", dzcore) : vars
-                      else return vars)
+    outputSettings <- optToOutputSettings opts
+    let format = outputFormat outputSettings
+    let writer = outputWriter outputSettings
+    let writerName = outputWriterName outputSettings
+    let writerOptions = outputWriterOptions outputSettings
+
+    let standalone = optStandalone opts || not (isTextFormat format) || pdfOutput
+
+    -- We don't want to send output to the terminal if the user
+    -- does 'pandoc -t docx input.txt'; though we allow them to
+    -- force this with '-o -'.  On posix systems, we detect
+    -- when stdout is being piped and allow output to stdout
+    -- in that case, but on Windows we can't.
+#ifdef _WINDOWS
+    let istty = True
+#else
+    istty <- liftIO $ queryTerminal stdOutput
+#endif
+    when (not (isTextFormat format) && istty && isNothing ( optOutputFile opts)) $
+      liftIO $ E.throwIO $ PandocAppError $
+              "Cannot write " ++ format ++ " output to terminal.\n" ++
+              "Specify an output file using the -o option, or " ++
+              "use '-o -' to force output to stdout."
+
 
     abbrevs <- Set.fromList . filter (not . null) . lines <$>
                case optAbbreviations opts of
                     Nothing -> UTF8.toString <$> readDataFile "abbreviations"
                     Just f  -> UTF8.toString <$> readFileStrict f
 
-    templ <- case optTemplate opts of
-                    _ | not standalone -> return Nothing
-                    Nothing -> Just <$> getDefaultTemplate format
-                    Just tp -> do
-                      -- strip off extensions
-                      let tp' = case takeExtension tp of
-                                     "" -> tp <.> format
-                                     _  -> tp
-                      Just . UTF8.toString <$>
-                            ((fst <$> fetchItem tp') `catchError`
-                             (\e ->
-                                 case e of
-                                      PandocResourceNotFound _ ->
-                                         readDataFile ("templates" </> tp')
-                                      _ -> throwError e))
-
     metadata <- if format == "jats" &&
                    isNothing (lookup "csl" (optMetadata opts)) &&
                    isNothing (lookup "citation-style" (optMetadata opts))
@@ -355,41 +221,6 @@ convertWithOpts opts = do
                            Right l' -> setTranslations l'
            Nothing -> setTranslations $ Lang "en" "" "US" []
 
-    let writerOptions = def {
-            writerTemplate         = templ
-          , writerVariables        = variables
-          , writerTabStop          = optTabStop opts
-          , writerTableOfContents  = optTableOfContents opts
-          , writerHTMLMathMethod   = optHTMLMathMethod opts
-          , writerIncremental      = optIncremental opts
-          , writerCiteMethod       = optCiteMethod opts
-          , writerNumberSections   = optNumberSections opts
-          , writerNumberOffset     = optNumberOffset opts
-          , writerSectionDivs      = optSectionDivs opts
-          , writerExtensions       = writerExts
-          , writerReferenceLinks   = optReferenceLinks opts
-          , writerReferenceLocation = optReferenceLocation opts
-          , writerDpi              = optDpi opts
-          , writerWrapText         = optWrapText opts
-          , writerColumns          = optColumns opts
-          , writerEmailObfuscation = optEmailObfuscation opts
-          , writerIdentifierPrefix = optIdentifierPrefix opts
-          , writerHtmlQTags        = optHtmlQTags opts
-          , writerTopLevelDivision = optTopLevelDivision opts
-          , writerListings         = optListings opts
-          , writerSlideLevel       = optSlideLevel opts
-          , writerHighlightStyle   = optHighlightStyle opts
-          , writerSetextHeaders    = optSetextHeaders opts
-          , writerEpubSubdirectory = optEpubSubdirectory opts
-          , writerEpubMetadata     = epubMetadata
-          , writerEpubFonts        = optEpubFonts opts
-          , writerEpubChapterLevel = optEpubChapterLevel opts
-          , writerTOCDepth         = optTOCDepth opts
-          , writerReferenceDoc     = optReferenceDoc opts
-          , writerSyntaxMap        = syntaxMap
-          , writerPreferAscii      = optAscii opts
-          }
-
     let readerOpts = def{
             readerStandalone = standalone
           , readerColumns = optColumns opts
@@ -412,7 +243,7 @@ convertWithOpts opts = do
                      (if extensionEnabled Ext_east_asian_line_breaks
                             readerExts &&
                          not (extensionEnabled Ext_east_asian_line_breaks
-                              writerExts &&
+                              (writerExtensions writerOptions) &&
                               writerWrapText writerOptions == WrapPreserve)
                          then (eastAsianLineBreakFilter :)
                          else id) $
@@ -450,7 +281,7 @@ convertWithOpts opts = do
 
     case writer of
       ByteStringWriter f -> f writerOptions doc >>= writeFnBinary outputFile
-      TextWriter f -> case maybePdfProg of
+      TextWriter f -> case outputPdfProgram outputSettings of
         Just pdfProg -> do
                 res <- makePDF pdfProg (optPdfEngineArgs opts) f
                         writerOptions doc
@@ -594,7 +425,3 @@ writerFn :: MonadIO m => IO.Newline -> FilePath -> Text -> m ()
 -- TODO this implementation isn't maximally efficient:
 writerFn eol "-" = liftIO . UTF8.putStrWith eol . T.unpack
 writerFn eol f   = liftIO . UTF8.writeFileWith eol f . T.unpack
-
-
-baseWriterName :: String -> String
-baseWriterName = takeWhile (\c -> c /= '+' && c /= '-')
diff --git a/src/Text/Pandoc/App/CommandLineOptions.hs b/src/Text/Pandoc/App/CommandLineOptions.hs
index d97b43b2f..9cbef3ee6 100644
--- a/src/Text/Pandoc/App/CommandLineOptions.hs
+++ b/src/Text/Pandoc/App/CommandLineOptions.hs
@@ -268,9 +268,8 @@ defaultOpts = Opt
     , optStripComments          = False
     }
 
-lookupHighlightStyle :: Maybe String -> IO (Maybe Style)
-lookupHighlightStyle Nothing = return Nothing
-lookupHighlightStyle (Just s)
+lookupHighlightStyle :: String -> IO (Maybe Style)
+lookupHighlightStyle s
   | takeExtension s == ".theme" = -- attempt to load KDE theme
     do contents <- B.readFile s
        case parseTheme contents of
diff --git a/src/Text/Pandoc/App/OutputSettings.hs b/src/Text/Pandoc/App/OutputSettings.hs
new file mode 100644
index 000000000..a7d5bee1b
--- /dev/null
+++ b/src/Text/Pandoc/App/OutputSettings.hs
@@ -0,0 +1,317 @@
+{-# LANGUAGE CPP                 #-}
+{-# LANGUAGE FlexibleContexts    #-}
+{-# LANGUAGE NoImplicitPrelude   #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE TupleSections       #-}
+{-
+Copyright (C) 2006-2018 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) 2006-2018 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.OutputSettings
+  ( OutputSettings (..)
+  , optToOutputSettings
+  ) where
+import Prelude
+import qualified Control.Exception as E
+import Control.Monad
+import Control.Monad.Except (catchError, throwError)
+import Control.Monad.Trans
+import Data.Char (toLower)
+import Data.List (find, isPrefixOf, isSuffixOf)
+import Data.Maybe (fromMaybe)
+import Skylighting (defaultSyntaxMap)
+import Skylighting.Parser (addSyntaxDefinition, parseSyntaxDefinition)
+import System.Exit (exitSuccess)
+import System.FilePath
+import System.IO (stdout)
+import Text.Pandoc
+import Text.Pandoc.App.CommandLineOptions (Opt (..), engines)
+import Text.Pandoc.BCP47 (Lang (..), parseBCP47)
+import qualified Text.Pandoc.UTF8 as UTF8
+
+-- | Settings specifying how document output should be produced.
+data OutputSettings = OutputSettings
+  { outputFormat :: String
+  , outputWriter :: Writer PandocIO
+  , outputWriterName :: String
+  , outputWriterOptions :: WriterOptions
+  , outputPdfProgram :: Maybe String
+  }
+
+readUtf8File :: PandocMonad m => FilePath -> m String
+readUtf8File = fmap UTF8.toString . readFileStrict
+
+-- | Get output settings from command line options.
+optToOutputSettings :: Opt -> PandocIO OutputSettings
+optToOutputSettings opts = do
+  let outputFile = fromMaybe "-" (optOutputFile opts)
+
+  when (optDumpArgs opts) . liftIO $ do
+    UTF8.hPutStrLn stdout outputFile
+    mapM_ (UTF8.hPutStrLn stdout) (optInputFiles opts)
+    exitSuccess
+
+  epubMetadata <- case optEpubMetadata opts of
+                         Nothing -> return Nothing
+                         Just fp -> Just <$> readUtf8File fp
+
+  let nonPdfWriterName Nothing  = defaultWriterName outputFile
+      nonPdfWriterName (Just x) = x
+
+  let pdfOutput = map toLower (takeExtension outputFile) == ".pdf"
+  (writerName, maybePdfProg) <-
+    if pdfOutput
+       then liftIO $ pdfWriterAndProg (optWriter opts) (optPdfEngine opts)
+       else return (nonPdfWriterName $ optWriter opts, Nothing)
+
+  let format = map toLower $ baseWriterName
+                 $ takeFileName writerName  -- in case path to lua script
+
+  -- disabling the custom writer for now
+  (writer, writerExts) <-
+            if ".lua" `isSuffixOf` format
+               then return (TextWriter
+                       (\o d -> writeCustom writerName o d)
+                               :: Writer PandocIO, mempty)
+               else case getWriter (map toLower writerName) of
+                         Left e  -> throwError $ PandocAppError $
+                           if format == "pdf"
+                              then e ++ "\n" ++ pdfIsNoWriterErrorMsg
+                              else e
+                         Right (w, es) -> return (w :: Writer PandocIO, es)
+
+
+  let standalone = optStandalone opts || not (isTextFormat format) || pdfOutput
+
+  let addStringAsVariable varname s vars = return $ (varname, s) : vars
+
+  let addSyntaxMap existingmap f = do
+        res <- liftIO (parseSyntaxDefinition f)
+        case res of
+              Left errstr -> throwError $ PandocSyntaxMapError errstr
+              Right syn   -> return $ addSyntaxDefinition syn existingmap
+
+  syntaxMap <- foldM addSyntaxMap defaultSyntaxMap
+                     (optSyntaxDefinitions opts)
+
+  -- 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
+
+  let addContentsAsVariable varname fp vars = do
+             s <- UTF8.toString <$> readFileStrict fp
+             return $ (varname, s) : vars
+
+  variables <-
+    withList (addStringAsVariable "sourcefile")
+             (reverse $ optInputFiles opts)
+             (("outputfile", fromMaybe "-" (optOutputFile opts))
+              : optVariables 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 ->  if format == "dzslides"
+                  then do
+                      dztempl <- UTF8.toString <$> readDataFile
+                                   ("dzslides" </> "template.html")
+                      let dzline = "<!-- {{{{ dzslides core"
+                      let dzcore = unlines
+                                 $ dropWhile (not . (dzline `isPrefixOf`))
+                                 $ lines dztempl
+                      return $ ("dzslides-core", dzcore) : vars
+                  else return vars)
+
+  templ <- case optTemplate opts of
+                  _ | not standalone -> return Nothing
+                  Nothing -> Just <$> getDefaultTemplate format
+                  Just tp -> do
+                    -- strip off extensions
+                    let tp' = case takeExtension tp of
+                                   "" -> tp <.> format
+                                   _  -> tp
+                    Just . UTF8.toString <$>
+                          ((fst <$> fetchItem tp') `catchError`
+                           (\e ->
+                               case e of
+                                    PandocResourceNotFound _ ->
+                                       readDataFile ("templates" </> tp')
+                                    _ -> throwError e))
+
+  case lookup "lang" (optMetadata opts) of
+         Just l  -> case parseBCP47 l of
+                         Left _   -> return ()
+                         Right l' -> setTranslations l'
+         Nothing -> setTranslations $ Lang "en" "" "US" []
+
+  let writerOpts = def {
+          writerTemplate         = templ
+        , writerVariables        = variables
+        , writerTabStop          = optTabStop opts
+        , writerTableOfContents  = optTableOfContents opts
+        , writerHTMLMathMethod   = optHTMLMathMethod opts
+        , writerIncremental      = optIncremental opts
+        , writerCiteMethod       = optCiteMethod opts
+        , writerNumberSections   = optNumberSections opts
+        , writerNumberOffset     = optNumberOffset opts
+        , writerSectionDivs      = optSectionDivs opts
+        , writerExtensions       = writerExts
+        , writerReferenceLinks   = optReferenceLinks opts
+        , writerReferenceLocation = optReferenceLocation opts
+        , writerDpi              = optDpi opts
+        , writerWrapText         = optWrapText opts
+        , writerColumns          = optColumns opts
+        , writerEmailObfuscation = optEmailObfuscation opts
+        , writerIdentifierPrefix = optIdentifierPrefix opts
+        , writerHtmlQTags        = optHtmlQTags opts
+        , writerTopLevelDivision = optTopLevelDivision opts
+        , writerListings         = optListings opts
+        , writerSlideLevel       = optSlideLevel opts
+        , writerHighlightStyle   = optHighlightStyle opts
+        , writerSetextHeaders    = optSetextHeaders opts
+        , writerEpubSubdirectory = optEpubSubdirectory opts
+        , writerEpubMetadata     = epubMetadata
+        , writerEpubFonts        = optEpubFonts opts
+        , writerEpubChapterLevel = optEpubChapterLevel opts
+        , writerTOCDepth         = optTOCDepth opts
+        , writerReferenceDoc     = optReferenceDoc opts
+        , writerSyntaxMap        = syntaxMap
+        , writerPreferAscii      = optAscii opts
+        }
+  return $ OutputSettings
+    { outputFormat = format
+    , outputWriter = writer
+    , outputWriterName = writerName
+    , outputWriterOptions = writerOpts
+    , outputPdfProgram = maybePdfProg
+    }
+
+-- 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"
+    ".muse"     -> "muse"
+    ".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"
+    ".fb2"      -> "fb2"
+    ".opml"     -> "opml"
+    ".icml"     -> "icml"
+    ".tei.xml"  -> "tei"
+    ".tei"      -> "tei"
+    ".ms"       -> "ms"
+    ".roff"     -> "ms"
+    ".pptx"     -> "pptx"
+    ['.',y]     | y `elem` ['1'..'9'] -> "man"
+    _           -> "html"
+
+baseWriterName :: String -> String
+baseWriterName = takeWhile (\c -> c /= '+' && c /= '-')
+
+pdfIsNoWriterErrorMsg :: String
+pdfIsNoWriterErrorMsg =
+  "To create a pdf using pandoc, use " ++
+  "-t latex|beamer|context|ms|html5" ++
+  "\nand specify an output file with " ++
+  ".pdf extension (-o filename.pdf)."
+
+pdfWriterAndProg :: Maybe String              -- ^ user-specified writer name
+                 -> Maybe String              -- ^ user-specified pdf-engine
+                 -> IO (String, Maybe String) -- ^ IO (writerName, maybePdfEngineProg)
+pdfWriterAndProg mWriter mEngine = do
+  let panErr msg = liftIO $ E.throwIO $ PandocAppError msg
+  case go mWriter mEngine of
+      Right (writ, prog) -> return (writ, Just prog)
+      Left err           -> panErr err
+    where
+      go Nothing Nothing       = Right ("latex", "pdflatex")
+      go (Just writer) Nothing = (writer,) <$> engineForWriter writer
+      go Nothing (Just engine) = (,engine) <$> writerForEngine (takeBaseName engine)
+      go (Just writer) (Just engine) =
+           case find (== (baseWriterName writer, takeBaseName engine)) engines of
+                Just _  -> Right (writer, engine)
+                Nothing -> Left $ "pdf-engine " ++ engine ++
+                           " is not compatible with output format " ++ writer
+
+      writerForEngine eng = case [f | (f,e) <- engines, e == eng] of
+                                 fmt : _ -> Right fmt
+                                 []      -> Left $
+                                   "pdf-engine " ++ eng ++ " not known"
+
+      engineForWriter "pdf" = Left pdfIsNoWriterErrorMsg
+      engineForWriter w = case [e |  (f,e) <- engines, f == baseWriterName w] of
+                                eng : _ -> Right eng
+                                []      -> Left $
+                                   "cannot produce pdf output from " ++ w
+
+isTextFormat :: String -> Bool
+isTextFormat s = s `notElem` ["odt","docx","epub2","epub3","epub","pptx"]