{-# LANGUAGE OverloadedStrings   #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE ViewPatterns        #-}
{- |
   Module      : Text.Pandoc.Writers.ConTeXt
   Copyright   : Copyright (C) 2007-2020 John MacFarlane
   License     : GNU GPL, version 2 or above

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

Conversion of 'Pandoc' format into ConTeXt.
-}
module Text.Pandoc.Writers.ConTeXt ( writeConTeXt ) where
import Control.Monad.State.Strict
import Data.Char (ord, isDigit)
import Data.List (intersperse)
import Data.Maybe (mapMaybe)
import Data.Text (Text)
import qualified Data.Text as T
import Network.URI (unEscapeString)
import Text.Pandoc.BCP47
import Text.Pandoc.Class.PandocMonad (PandocMonad, report, toLang)
import Text.Pandoc.Definition
import Text.Pandoc.ImageSize
import Text.Pandoc.Logging
import Text.Pandoc.Options
import Text.DocLayout
import Text.Pandoc.Shared
import Text.Pandoc.Templates (renderTemplate)
import Text.Pandoc.Walk (query)
import Text.Pandoc.Writers.Shared
import Text.Printf (printf)

data WriterState =
  WriterState { stNextRef          :: Int  -- number of next URL reference
              , stOrderedListLevel :: Int  -- level of ordered list
              , stOptions          :: WriterOptions -- writer options
              , stHasCslRefs       :: Bool -- has CSL citations
              , stCslHangingIndent :: Bool -- CSL hanging indent
              }

data Tabl = Xtb | Ntb deriving (Show, Eq)

orderedListStyles :: [Char]
orderedListStyles = cycle "narg"

-- | Convert Pandoc to ConTeXt.
writeConTeXt :: PandocMonad m => WriterOptions -> Pandoc -> m Text
writeConTeXt options document =
  let defaultWriterState = WriterState { stNextRef = 1
                                       , stOrderedListLevel = 0
                                       , stOptions = options
                                       , stHasCslRefs = False
                                       , stCslHangingIndent = False
                                       }
  in evalStateT (pandocToConTeXt options document) defaultWriterState

type WM = StateT WriterState

pandocToConTeXt :: PandocMonad m => WriterOptions -> Pandoc -> WM m Text
pandocToConTeXt options (Pandoc meta blocks) = do
  let colwidth = if writerWrapText options == WrapAuto
                    then Just $ writerColumns options
                    else Nothing
  metadata <- metaToContext options
              blockListToConTeXt
              (fmap chomp . inlineListToConTeXt)
              meta
  main <- blockListToConTeXt $ makeSections False Nothing blocks
  let layoutFromMargins = mconcat $ intersperse ("," :: Doc Text) $
                          mapMaybe (\(x,y) ->
                                ((x <> "=") <>) <$> getField y metadata)
                              [("leftmargin","margin-left")
                              ,("rightmargin","margin-right")
                              ,("top","margin-top")
                              ,("bottom","margin-bottom")
                              ]
  mblang <- fromBCP47 (getLang options meta)
  st <- get
  let context =   defField "toc" (writerTableOfContents options)
                $ defField "placelist"
                   (mconcat . intersperse ("," :: Doc Text) $
                     take (writerTOCDepth options +
                           case writerTopLevelDivision options of
                             TopLevelPart    -> 0
                             TopLevelChapter -> 0
                             _               -> 1)
                       ["chapter","section","subsection","subsubsection",
                        "subsubsubsection","subsubsubsubsection"])
                $ defField "body" main
                $ defField "layout" layoutFromMargins
                $ defField "number-sections" (writerNumberSections options)
                $ defField "csl-refs" (stHasCslRefs st)
                $ defField "csl-hanging-indent" (stCslHangingIndent st)
                $ maybe id (\l ->
                     defField "context-lang" (literal l :: Doc Text)) mblang
                $ (case T.unpack . render Nothing <$>
                      getField "papersize" metadata of
                        Just (('a':d:ds) :: String)
                          | all isDigit (d:ds) -> resetField "papersize"
                                                   (T.pack ('A':d:ds))
                        _                     -> id)
                $ (case T.toLower $ lookupMetaString "pdfa" meta of
                        "true" -> resetField "pdfa" (T.pack "1b:2005")
                        _                     -> id) metadata
  let context' = defField "context-dir" (maybe mempty toContextDir
                                         $ getField "dir" context) context
  return $ render colwidth $
    case writerTemplate options of
       Nothing  -> main
       Just tpl -> renderTemplate tpl context'

-- change rtl to r2l, ltr to l2r
toContextDir :: Doc Text -> Doc Text
toContextDir = fmap (\t -> case t of
                              "ltr" -> "l2r"
                              "rtl" -> "r2l"
                              _     -> t)

-- | escape things as needed for ConTeXt
escapeCharForConTeXt :: WriterOptions -> Char -> Text
escapeCharForConTeXt opts ch =
 let ligatures = isEnabled Ext_smart opts in
 case ch of
    '{'      -> "\\{"
    '}'      -> "\\}"
    '\\'     -> "\\letterbackslash{}"
    '$'      -> "\\$"
    '|'      -> "\\letterbar{}"
    '%'      -> "\\letterpercent{}"
    '~'      -> "\\lettertilde{}"
    '#'      -> "\\#"
    '['      -> "{[}"
    ']'      -> "{]}"
    '\160'   -> "~"
    '\x2014' | ligatures -> "---"
    '\x2013' | ligatures -> "--"
    '\x2019' | ligatures -> "'"
    '\x2026' -> "\\ldots{}"
    x        -> T.singleton x

-- | Escape string for ConTeXt
stringToConTeXt :: WriterOptions -> Text -> Text
stringToConTeXt opts = T.concatMap (escapeCharForConTeXt opts)

-- | Sanitize labels
toLabel :: Text -> Text
toLabel z = T.concatMap go z
 where go x
         | x `elem` ("\\#[]\",{}%()|=" :: String) = "ux" <> T.pack (printf "%x" (ord x))
         | otherwise = T.singleton x

-- | Convert Pandoc block element to ConTeXt.
blockToConTeXt :: PandocMonad m => Block -> WM m (Doc Text)
blockToConTeXt Null = return empty
blockToConTeXt (Div attr@(_,"section":_,_)
                 (Header level _ title' : xs)) = do
  header' <- sectionHeader attr level title'
  footer' <- sectionFooter attr level
  innerContents <- blockListToConTeXt xs
  return $ header' $$ innerContents $$ footer'
blockToConTeXt (Plain lst) = inlineListToConTeXt lst
-- title beginning with fig: indicates that the image is a figure
blockToConTeXt (Para [Image attr txt (src,tgt)])
  | Just _ <- T.stripPrefix "fig:" tgt
  = do
      capt <- inlineListToConTeXt txt
      img  <- inlineToConTeXt (Image attr txt (src, ""))
      let (ident, _, _) = attr
          label = if T.null ident
                  then empty
                  else "[]" <> brackets (literal $ toLabel ident)
      return $ blankline $$ "\\placefigure" <> label <> braces capt <> img <> blankline
blockToConTeXt (Para lst) = do
  contents <- inlineListToConTeXt lst
  return $ contents <> blankline
blockToConTeXt (LineBlock lns) = do
  doclines <- nowrap . vcat <$> mapM inlineListToConTeXt lns
  return $ "\\startlines" $$ doclines $$ "\\stoplines" <> blankline
blockToConTeXt (BlockQuote lst) = do
  contents <- blockListToConTeXt lst
  return $ "\\startblockquote" $$ nest 0 contents $$ "\\stopblockquote" <> blankline
blockToConTeXt (CodeBlock _ str) =
  return $ flush ("\\starttyping" <> cr <> literal str <> cr <> "\\stoptyping") $$ blankline
  -- blankline because \stoptyping can't have anything after it, inc. '}'
blockToConTeXt b@(RawBlock f str)
  | f == Format "context" || f == Format "tex" = return $ literal str <> blankline
  | otherwise = empty <$ report (BlockNotRendered b)
blockToConTeXt (Div ("refs",classes,_) bs) = do
  modify $ \st -> st{ stHasCslRefs = True
                    , stCslHangingIndent = "hanging-indent" `elem` classes }
  inner <- blockListToConTeXt bs
  return $ "\\startcslreferences" $$ inner $$ "\\stopcslreferences"
blockToConTeXt (Div (ident,_,kvs) bs) = do
  let align dir txt = "\\startalignment[" <> dir <> "]" $$ txt $$ "\\stopalignment"
  mblang <- fromBCP47 (lookup "lang" kvs)
  let wrapRef txt = if T.null ident
                       then txt
                       else ("\\reference" <> brackets (literal $ toLabel ident) <>
                              braces empty <> "%") $$ txt
      wrapDir = case lookup "dir" kvs of
                  Just "rtl" -> align "righttoleft"
                  Just "ltr" -> align "lefttoright"
                  _          -> id
      wrapLang txt = case mblang of
                       Just lng -> "\\start\\language["
                                     <> literal lng <> "]" $$ txt $$ "\\stop"
                       Nothing  -> txt
      wrapBlank txt = blankline <> txt <> blankline
  (wrapBlank . wrapLang . wrapDir . wrapRef) <$> blockListToConTeXt bs
blockToConTeXt (BulletList lst) = do
  contents <- mapM listItemToConTeXt lst
  return $ ("\\startitemize" <> if isTightList lst
                                   then brackets "packed"
                                   else empty) $$
    vcat contents $$ literal "\\stopitemize" <> blankline
blockToConTeXt (OrderedList (start, style', delim) lst) = do
    st <- get
    let level = stOrderedListLevel st
    put st {stOrderedListLevel = level + 1}
    contents <- mapM listItemToConTeXt lst
    put st {stOrderedListLevel = level}
    let start' = if start == 1 then "" else "start=" <> tshow start
    let delim' = case delim of
                        DefaultDelim -> ""
                        Period       -> "stopper=."
                        OneParen     -> "stopper=)"
                        TwoParens    -> "left=(,stopper=)"
    let width = maximum $ map T.length $ take (length contents)
                          (orderedListMarkers (start, style', delim))
    let width' = (toEnum width + 1) / 2
    let width'' = if width' > (1.5 :: Double)
                     then "width=" <> tshow width' <> "em"
                     else ""
    let specs2Items = filter (not . T.null) [start', delim', width'']
    let specs2 = if null specs2Items
                    then ""
                    else "[" <> T.intercalate "," specs2Items <> "]"
    let style'' = '[': (case style' of
                          DefaultStyle -> orderedListStyles !! level
                          Decimal      -> 'n'
                          Example      -> 'n'
                          LowerRoman   -> 'r'
                          UpperRoman   -> 'R'
                          LowerAlpha   -> 'a'
                          UpperAlpha   -> 'A') :
                       if isTightList lst then ",packed]" else "]"
    let specs = T.pack style'' <> specs2
    return $ "\\startitemize" <> literal specs $$ vcat contents $$
             "\\stopitemize" <> blankline
blockToConTeXt (DefinitionList lst) =
  liftM vcat $ mapM defListItemToConTeXt lst
blockToConTeXt HorizontalRule = return $ "\\thinrule" <> blankline
-- If this is ever executed, provide a default for the reference identifier.
blockToConTeXt (Header level attr lst) = sectionHeader attr level lst
blockToConTeXt (Table caption aligns widths heads rows) = do
    opts <- gets stOptions
    let tabl = if isEnabled Ext_ntb opts
          then Ntb
          else Xtb
    captionText <- inlineListToConTeXt caption
    headers <- if all null heads
               then return empty
               else tableRowToConTeXt tabl aligns widths heads
    rows' <- mapM (tableRowToConTeXt tabl aligns widths) rows
    body <- tableToConTeXt tabl headers rows'
    return $ "\\startplacetable" <> brackets (
      if null caption
        then "location=none"
        else "title=" <> braces captionText
      ) $$ body $$ "\\stopplacetable" <> blankline

tableToConTeXt :: PandocMonad m
               => Tabl -> Doc Text -> [Doc Text] -> WM m (Doc Text)
tableToConTeXt Xtb heads rows =
  return $ "\\startxtable" $$
    (if isEmpty heads
      then empty
      else "\\startxtablehead[head]" $$ heads $$ "\\stopxtablehead") $$
    (if null rows
      then empty
      else "\\startxtablebody[body]" $$ vcat (init rows) $$ "\\stopxtablebody" $$
           "\\startxtablefoot[foot]" $$ last rows $$ "\\stopxtablefoot") $$
    "\\stopxtable"
tableToConTeXt Ntb heads rows =
  return $ "\\startTABLE" $$
    (if isEmpty heads
      then empty
      else "\\startTABLEhead" $$ heads $$ "\\stopTABLEhead") $$
    (if null rows
      then empty
      else "\\startTABLEbody" $$ vcat (init rows) $$ "\\stopTABLEbody" $$
           "\\startTABLEfoot" $$ last rows $$ "\\stopTABLEfoot") $$
    "\\stopTABLE"

tableRowToConTeXt :: PandocMonad m => Tabl -> [Alignment] -> [Double] -> [[Block]] -> WM m (Doc Text)
tableRowToConTeXt Xtb aligns widths cols = do
  cells <- mapM (tableColToConTeXt Xtb) $ zip3 aligns widths cols
  return $ "\\startxrow" $$ vcat cells $$ "\\stopxrow"
tableRowToConTeXt Ntb aligns widths cols = do
  cells <- mapM (tableColToConTeXt Ntb) $ zip3 aligns widths cols
  return $ vcat cells $$ "\\NC\\NR"

tableColToConTeXt :: PandocMonad m => Tabl -> (Alignment, Double, [Block]) -> WM m (Doc Text)
tableColToConTeXt tabl (align, width, blocks) = do
  cellContents <- blockListToConTeXt blocks
  let colwidth = if width == 0
        then empty
        else "width=" <> braces (text (printf "%.2f\\textwidth" width))
  let halign = alignToConTeXt align
  let options = (if isEmpty keys
                 then empty
                 else brackets keys) <> space
        where keys = hcat $ intersperse "," $ filter (not . isEmpty) [halign, colwidth]
  tableCellToConTeXt tabl options cellContents

tableCellToConTeXt :: PandocMonad m
                   => Tabl -> Doc Text -> Doc Text -> WM m (Doc Text)
tableCellToConTeXt Xtb options cellContents =
  return $ "\\startxcell" <> options <> cellContents <> " \\stopxcell"
tableCellToConTeXt Ntb options cellContents =
  return $ "\\NC" <> options <> cellContents

alignToConTeXt :: Alignment -> Doc Text
alignToConTeXt align = case align of
                         AlignLeft    -> "align=right"
                         AlignRight   -> "align=left"
                         AlignCenter  -> "align=middle"
                         AlignDefault -> empty

listItemToConTeXt :: PandocMonad m => [Block] -> WM m (Doc Text)
listItemToConTeXt list = (("\\item" $$) . nest 2) <$> blockListToConTeXt list

defListItemToConTeXt :: PandocMonad m => ([Inline], [[Block]]) -> WM m (Doc Text)
defListItemToConTeXt (term, defs) = do
  term' <- inlineListToConTeXt term
  def'  <- liftM vsep $ mapM blockListToConTeXt defs
  return $ "\\startdescription" <> braces term' $$ nest 2 def' $$
           "\\stopdescription" <> blankline

-- | Convert list of block elements to ConTeXt.
blockListToConTeXt :: PandocMonad m => [Block] -> WM m (Doc Text)
blockListToConTeXt lst = liftM vcat $ mapM blockToConTeXt lst

-- | Convert list of inline elements to ConTeXt.
inlineListToConTeXt :: PandocMonad m
                    => [Inline]  -- ^ Inlines to convert
                    -> WM m (Doc Text)
inlineListToConTeXt lst = liftM hcat $ mapM inlineToConTeXt $ addStruts lst
  -- We add a \strut after a line break that precedes a space,
  -- or the space gets swallowed
  where addStruts (LineBreak : s : xs) | isSpacey s =
           LineBreak : RawInline (Format "context") "\\strut " : s :
             addStruts xs
        addStruts (x:xs) = x : addStruts xs
        addStruts [] = []
        isSpacey Space                               = True
        isSpacey (Str (T.uncons -> Just ('\160',_))) = True
        isSpacey _                                   = False

-- | Convert inline element to ConTeXt
inlineToConTeXt :: PandocMonad m
                => Inline    -- ^ Inline to convert
                -> WM m (Doc Text)
inlineToConTeXt (Emph lst) = do
  contents <- inlineListToConTeXt lst
  return $ braces $ "\\em " <> contents
inlineToConTeXt (Strong lst) = do
  contents <- inlineListToConTeXt lst
  return $ braces $ "\\bf " <> contents
inlineToConTeXt (Strikeout lst) = do
  contents <- inlineListToConTeXt lst
  return $ "\\overstrikes" <> braces contents
inlineToConTeXt (Superscript lst) = do
  contents <- inlineListToConTeXt lst
  return $ "\\high" <> braces contents
inlineToConTeXt (Subscript lst) = do
  contents <- inlineListToConTeXt lst
  return $ "\\low" <> braces contents
inlineToConTeXt (SmallCaps lst) = do
  contents <- inlineListToConTeXt lst
  return $ braces $ "\\sc " <> contents
inlineToConTeXt (Code _ str) | not ('{' `elemText` str || '}' `elemText` str) =
  return $ "\\type" <> braces (literal str)
inlineToConTeXt (Code _ str) = do
  opts <- gets stOptions
  return $ "\\mono" <> braces (literal $ stringToConTeXt opts str)
inlineToConTeXt (Quoted SingleQuote lst) = do
  contents <- inlineListToConTeXt lst
  return $ "\\quote" <> braces contents
inlineToConTeXt (Quoted DoubleQuote lst) = do
  contents <- inlineListToConTeXt lst
  return $ "\\quotation" <> braces contents
inlineToConTeXt (Cite _ lst) = inlineListToConTeXt lst
inlineToConTeXt (Str str) = do
  opts <- gets stOptions
  return $ literal $ stringToConTeXt opts str
inlineToConTeXt (Math InlineMath str) =
  return $ char '$' <> literal str <> char '$'
inlineToConTeXt (Math DisplayMath str) =
  return $ literal "\\startformula "  <> literal str <> literal " \\stopformula" <> space
inlineToConTeXt il@(RawInline f str)
  | f == Format "tex" || f == Format "context" = return $ literal str
  | otherwise = empty <$ report (InlineNotRendered il)
inlineToConTeXt LineBreak = return $ literal "\\crlf" <> cr
inlineToConTeXt SoftBreak = do
  wrapText <- gets (writerWrapText . stOptions)
  return $ case wrapText of
               WrapAuto     -> space
               WrapNone     -> space
               WrapPreserve -> cr
inlineToConTeXt Space = return space
-- Handle HTML-like internal document references to sections
inlineToConTeXt (Link _ txt (T.uncons -> Just ('#', ref), _)) = do
  opts <- gets stOptions
  contents <-  inlineListToConTeXt txt
  let ref' = toLabel $ stringToConTeXt opts ref
  return $ literal "\\goto"
           <> braces contents
           <> brackets (literal ref')

inlineToConTeXt (Link _ txt (src, _)) = do
  let isAutolink = txt == [Str (T.pack $ unEscapeString $ T.unpack src)]
  st <- get
  let next = stNextRef st
  put $ st {stNextRef = next + 1}
  let ref = "url" <> tshow next
  contents <-  inlineListToConTeXt txt
  return $ "\\useURL"
           <> brackets (literal ref)
           <> brackets (literal $ escapeStringUsing [('#',"\\#"),('%',"\\%")] src)
           <> (if isAutolink
                  then empty
                  else brackets empty <> brackets contents)
           <> "\\from"
           <> brackets (literal ref)
inlineToConTeXt (Image attr@(_,cls,_) _ (src, _)) = do
  opts <- gets stOptions
  let showDim dir = let d = literal (tshow dir) <> "="
                    in case dimension dir attr of
                         Just (Pixel a)   ->
                           [d <> literal (showInInch opts (Pixel a)) <> "in"]
                         Just (Percent a) ->
                           [d <> literal (showFl (a / 100)) <> "\\textwidth"]
                         Just dim         ->
                           [d <> literal (tshow dim)]
                         Nothing          ->
                           []
      dimList = showDim Width ++ showDim Height
      dims = if null dimList
                then empty
                else brackets $ mconcat (intersperse "," dimList)
      clas = if null cls
                then empty
                else brackets $ literal $ toLabel $ head cls
      -- Use / for path separators on Windows; see #4918
      fixPathSeparators = T.map $ \c -> case c of
                                          '\\' -> '/'
                                          _    -> c
      src' = fixPathSeparators $
             if isURI src
                then src
                else T.pack $ unEscapeString $ T.unpack src
  return $ braces $ "\\externalfigure" <> brackets (literal src') <> dims <> clas
inlineToConTeXt (Note contents) = do
  contents' <- blockListToConTeXt contents
  let codeBlock x@(CodeBlock _ _) = [x]
      codeBlock _                 = []
  let codeBlocks = query codeBlock contents
  return $ if null codeBlocks
              then literal "\\footnote{" <> nest 2 (chomp contents') <> char '}'
              else literal "\\startbuffer " <> nest 2 (chomp contents') <>
                   literal "\\stopbuffer\\footnote{\\getbuffer}"
inlineToConTeXt (Span (_,_,kvs) ils) = do
  mblang <- fromBCP47 (lookup "lang" kvs)
  let wrapDir txt = case lookup "dir" kvs of
                      Just "rtl" -> braces $ "\\righttoleft " <> txt
                      Just "ltr" -> braces $ "\\lefttoright " <> txt
                      _          -> txt
      wrapLang txt = case mblang of
                       Just lng -> braces ("\\language" <>
                                           brackets (literal lng) <> txt)
                       Nothing -> txt
  (wrapLang . wrapDir) <$> inlineListToConTeXt ils

-- | Craft the section header, inserting the section reference, if supplied.
sectionHeader :: PandocMonad m
              => Attr
              -> Int
              -> [Inline]
              -> WM m (Doc Text)
sectionHeader (ident,classes,kvs) hdrLevel lst = do
  opts <- gets stOptions
  contents <- inlineListToConTeXt lst
  levelText <- sectionLevelToText opts (ident,classes,kvs) hdrLevel
  let ident' = if T.null ident
               then empty
               else "reference=" <> braces (literal (toLabel ident))
  let contents' = if isEmpty contents
                  then empty
                  else "title=" <> braces contents
  let options = if isEmpty keys || isEmpty levelText
                then empty
                else brackets keys
        where keys = hcat $ intersperse "," $ filter (not . isEmpty) [contents', ident']
  let starter = if writerSectionDivs opts
                then "\\start"
                else "\\"
  return $ starter <> levelText <> options <> blankline

-- | Craft the section footer
sectionFooter :: PandocMonad m => Attr -> Int -> WM m (Doc Text)
sectionFooter attr hdrLevel = do
  opts <- gets stOptions
  levelText <- sectionLevelToText opts attr hdrLevel
  return $ if writerSectionDivs opts
           then "\\stop" <> levelText <> blankline
           else empty

-- | Generate a textual representation of the section level
sectionLevelToText :: PandocMonad m => WriterOptions -> Attr -> Int -> WM m (Doc Text)
sectionLevelToText opts (_,classes,_) hdrLevel = do
  let level' = case writerTopLevelDivision opts of
                 TopLevelPart    -> hdrLevel - 2
                 TopLevelChapter -> hdrLevel - 1
                 TopLevelSection -> hdrLevel
                 TopLevelDefault -> hdrLevel
  let (section, chapter) = if "unnumbered" `elem` classes
                              then (literal "subject", literal "title")
                              else (literal "section", literal "chapter")
  return $ case level' of
             -1         -> literal "part"
             0          -> chapter
             n | n >= 1 -> text (concat (replicate (n - 1) "sub"))
                           <> section
             _          -> empty -- cannot happen

fromBCP47 :: PandocMonad m => Maybe Text -> WM m (Maybe Text)
fromBCP47 mbs = fromBCP47' <$> toLang mbs

-- Takes a list of the constituents of a BCP 47 language code
-- and irons out ConTeXt's exceptions
-- https://tools.ietf.org/html/bcp47#section-2.1
-- http://wiki.contextgarden.net/Language_Codes
fromBCP47' :: Maybe Lang -> Maybe Text
fromBCP47' (Just (Lang "ar" _ "SY" _)     ) = Just "ar-sy"
fromBCP47' (Just (Lang "ar" _ "IQ" _)     ) = Just "ar-iq"
fromBCP47' (Just (Lang "ar" _ "JO" _)     ) = Just "ar-jo"
fromBCP47' (Just (Lang "ar" _ "LB" _)     ) = Just "ar-lb"
fromBCP47' (Just (Lang "ar" _ "DZ" _)     ) = Just "ar-dz"
fromBCP47' (Just (Lang "ar" _ "MA" _)     ) = Just "ar-ma"
fromBCP47' (Just (Lang "de" _ _ ["1901"]) ) = Just "deo"
fromBCP47' (Just (Lang "de" _ "DE" _)     ) = Just "de-de"
fromBCP47' (Just (Lang "de" _ "AT" _)     ) = Just "de-at"
fromBCP47' (Just (Lang "de" _ "CH" _)     ) = Just "de-ch"
fromBCP47' (Just (Lang "el" _ _ ["poly"]) ) = Just "agr"
fromBCP47' (Just (Lang "en" _ "US" _)     ) = Just "en-us"
fromBCP47' (Just (Lang "en" _ "GB" _)     ) = Just "en-gb"
fromBCP47' (Just (Lang "grc"_  _ _)       ) = Just "agr"
fromBCP47' (Just (Lang "el" _ _ _)        ) = Just "gr"
fromBCP47' (Just (Lang "eu" _ _ _)        ) = Just "ba"
fromBCP47' (Just (Lang "he" _ _ _)        ) = Just "il"
fromBCP47' (Just (Lang "jp" _ _ _)        ) = Just "ja"
fromBCP47' (Just (Lang "uk" _ _ _)        ) = Just "ua"
fromBCP47' (Just (Lang "vi" _ _ _)        ) = Just "vn"
fromBCP47' (Just (Lang "zh" _ _ _)        ) = Just "cn"
fromBCP47' (Just (Lang l _ _ _)           ) = Just l
fromBCP47' Nothing                          = Nothing