module Text.Pandoc.Readers.OPML ( readOPML ) where
import Data.Char (toUpper)
import Text.Pandoc.Options
import Text.Pandoc.Definition
import Text.Pandoc.Builder
import Text.Pandoc.Readers.HTML (readHtml)
import Text.Pandoc.Readers.Markdown (readMarkdown)
import Text.XML.Light
import Text.Pandoc.Compat.TagSoupEntity (lookupEntity)
import Data.Generics
import Data.Monoid
import Control.Monad.State
import Control.Applicative ((<$>), (<$))

type OPML = State OPMLState

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

readOPML :: ReaderOptions -> String -> Pandoc
readOPML _ inp  = setTitle (opmlDocTitle st')
                   $ setAuthors (opmlDocAuthors st')
                   $ setDate (opmlDocDate st')
                   $ doc $ mconcat bs
  where (bs, st') = runState (mapM parseBlock $ normalizeTree $ parseXML inp)
                             OPMLState{ opmlSectionLevel = 0
                                    , opmlDocTitle = mempty
                                    , opmlDocAuthors = []
                                    , opmlDocDate = mempty
                                    }

-- 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 = maybe (map toUpper e) (:[]) (lookupEntity e)

-- convenience function to get an attribute value, defaulting to ""
attrValue :: String -> Element -> String
attrValue attr elt =
  case lookupAttrBy (\x -> qName x == attr) (elAttribs elt) of
    Just z  -> z
    Nothing -> ""

asHtml :: String -> Inlines
asHtml s = case readHtml def s of
                Pandoc _ [Plain ils] -> fromList ils
                _ -> mempty

asMarkdown :: String -> Blocks
asMarkdown s = fromList bs
  where Pandoc _ bs = readMarkdown def s

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

parseBlock :: Content -> OPML 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 let headerText = asHtml $ attrValue "text" e
                     let 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