    {-# LANGUAGE NoImplicitPrelude #-}
    {-
    Copyright (C) 2013-2018 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.Readers.OPML
       Copyright   : Copyright (C) 2013-2018 John MacFarlane
       License     : GNU GPL, version 2 or above

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

    Conversion of OPML to 'Pandoc' document.
    -}

    module Text.Pandoc.Readers.OPML ( readOPML ) where
    import Prelude
    import Control.Monad.State.Strict
    import Data.Char (toUpper)
    import Data.Default
    import Data.Generics
    import Data.Maybe (fromMaybe)
    import Data.Text (Text, pack, unpack)
    import Text.HTML.TagSoup.Entity (lookupEntity)
    import Text.Pandoc.Builder
    import Text.Pandoc.Class (PandocMonad)
    import Text.Pandoc.Options
    import Text.Pandoc.Readers.HTML (readHtml)
    import Text.Pandoc.Readers.Markdown (readMarkdown)
    import Text.Pandoc.Shared (crFilter, blocksToInlines')
    import Text.XML.Light

    type OPML m = StateT OPMLState m

    data OPMLState = OPMLState{
                            opmlSectionLevel :: Int
                          , opmlDocTitle     :: Inlines
                          , opmlDocAuthors   :: [Inlines]
                          , opmlDocDate      :: Inlines
                          , opmlOptions      :: ReaderOptions
                          } deriving Show

    instance Default OPMLState where
      def = OPMLState{ opmlSectionLevel = 0
                     , opmlDocTitle = mempty
                     , opmlDocAuthors = []
                     , opmlDocDate = mempty
                     , opmlOptions = def
                     }

    readOPML :: PandocMonad m => ReaderOptions -> Text -> m Pandoc
    readOPML opts inp  = do
      (bs, st') <- runStateT
                     (mapM parseBlock $ normalizeTree $
                        parseXML (unpack (crFilter inp))) def{ opmlOptions = opts }
      return $
        setTitle (opmlDocTitle st') $
        setAuthors (opmlDocAuthors st') $
        setDate (opmlDocDate st') $
        doc $ mconcat bs

    -- normalize input, consolidating adjacent Text and CRef elements
    normalizeTree :: [Content] -> [Content]
    normalizeTree = everywhere (mkT go)
      where go :: [Content] -> [Content]
            go (Text (CData CDataRaw _ _):xs) = xs
            go (Text (CData CDataText s1 z):Text (CData CDataText s2 _):xs) =
               Text (CData CDataText (s1 ++ s2) z):xs
            go (Text (CData CDataText s1 z):CRef r:xs) =
               Text (CData CDataText (s1 ++ convertEntity r) z):xs
            go (CRef r:Text (CData CDataText s1 z):xs) =
                 Text (CData CDataText (convertEntity r ++ s1) z):xs
            go (CRef r1:CRef r2:xs) =
                 Text (CData CDataText (convertEntity r1 ++ convertEntity r2) Nothing):xs
            go xs = xs

    convertEntity :: String -> String
    convertEntity e = Data.Maybe.fromMaybe (map toUpper e) (lookupEntity e)

    -- convenience function to get an attribute value, defaulting to ""
    attrValue :: String -> Element -> String
    attrValue attr elt =
      fromMaybe "" (lookupAttrBy (\x -> qName x == attr) (elAttribs elt))

    -- exceptT :: PandocMonad m => Either PandocError a -> OPML m a
    -- exceptT = either throwError return

    asHtml :: PandocMonad m => String -> OPML m Inlines
    asHtml s = do
      opts <- gets opmlOptions
      Pandoc _ bs <- readHtml def{ readerExtensions = readerExtensions opts } (pack s)
      return $ blocksToInlines' bs

    asMarkdown :: PandocMonad m => String -> OPML m Blocks
    asMarkdown s = do
      opts <- gets opmlOptions
      Pandoc _ bs <- readMarkdown def{ readerExtensions = readerExtensions opts }  (pack s)
      return $ fromList bs

    getBlocks :: PandocMonad m => Element -> OPML m Blocks
    getBlocks e =  mconcat <$> mapM parseBlock (elContent e)

    parseBlock :: PandocMonad m => Content -> OPML m Blocks
    parseBlock (Elem e) =
      case qName (elName e) of
            "ownerName"    -> mempty <$ modify (\st ->
                                  st{opmlDocAuthors = [text $ strContent e]})
            "dateModified" -> mempty <$ modify (\st ->
                                  st{opmlDocDate = text $ strContent e})
            "title"        -> mempty <$ modify (\st ->
                                  st{opmlDocTitle = text $ strContent e})
            "outline" -> gets opmlSectionLevel >>= sect . (+1)
            "?xml"  -> return mempty
            _       -> getBlocks e
       where sect n = do headerText <- asHtml $ attrValue "text" e
                         noteBlocks <- asMarkdown $ attrValue "_note" e
                         modify $ \st -> st{ opmlSectionLevel = n }
                         bs <- getBlocks e
                         modify $ \st -> st{ opmlSectionLevel = n - 1 }
                         let headerText' = case map toUpper (attrValue "type" e) of
                                                 "LINK"  -> link
                                                   (attrValue "url" e) "" headerText
                                                 _ -> headerText
                         return $ header n headerText' <> noteBlocks <> bs
    parseBlock _ = return mempty