-- |An RDF serializer for Turtle 
-- <http://www.w3.org/TeamSubmission/turtle/>.

module Text.RDF.RDF4H.TurtleSerializer(
  TurtleSerializer(TurtleSerializer)
)

where

import Data.RDF.Types
import Data.RDF.Query
import Data.RDF.Namespace hiding (rdf)
import qualified Data.Text as T
import qualified Data.Text.IO as T
import Data.Map(Map)
import qualified Data.Map as Map
import Data.List
import Control.Monad
import System.IO

data TurtleSerializer = TurtleSerializer (Maybe T.Text) PrefixMappings

instance RdfSerializer TurtleSerializer where
  hWriteRdf  (TurtleSerializer docUrl pms) h rdf = _writeRdf h docUrl (addPrefixMappings rdf pms False)
  writeRdf   s = hWriteRdf s stdout
  hWriteH  (TurtleSerializer _ pms) h rdf = writeHeader h (baseUrl rdf) (mergePrefixMappings (prefixMappings rdf) pms)
  writeH   s = hWriteRdf s stdout
  -- TODO: should use mdUrl to render <> where appropriate
  hWriteTs (TurtleSerializer docUrl pms) h = writeTriples h docUrl pms
  writeTs s   = hWriteTs s stdout
  hWriteT  (TurtleSerializer docUrl pms) h = writeTriple h docUrl pms
  writeT  s   = hWriteT s stdout
  hWriteN  (TurtleSerializer docUrl (PrefixMappings pms)) h n = writeNode h docUrl n pms
  writeN  s   = hWriteN s stdout 

-- TODO: writeRdf currently merges standard namespace prefix mappings with
-- the ones that the RDF already contains, so that if the RDF has none
-- (e.g., was parsed from ntriples RDF) the output still uses prefix for
-- common mappings like rdf, owl, and the like. This behavior should be
-- configurable somehow, so that if the user really doesn't want any extra
-- prefix declarations added, that is possible.

_writeRdf :: RDF rdf => Handle -> Maybe T.Text -> rdf -> IO ()
_writeRdf h mdUrl rdf =
  writeHeader h bUrl pms' >> writeTriples h mdUrl pms' ts >> hPutChar h '\n'
  where
    bUrl   = baseUrl rdf
    -- a merged set of prefix mappings using those from the standard_ns_mappings
    -- that are not defined already (union is left-biased).
    pms'   = PrefixMappings $ Map.union (asMap $ prefixMappings rdf) (asMap standard_ns_mappings)
    asMap (PrefixMappings x) = x
    ts     = triplesOf rdf

writeHeader :: Handle -> Maybe BaseUrl -> PrefixMappings -> IO ()
writeHeader h bUrl pms = writeBase h bUrl >> writePrefixes h pms

writeBase :: Handle -> Maybe BaseUrl -> IO ()
writeBase _ Nothing               =
  return ()
writeBase h (Just (BaseUrl bUrl)) =
  hPutStr h "@base " >> hPutChar h '<' >> T.hPutStr h bUrl >> hPutStr h "> ." >> hPutChar h '\n'

writePrefixes :: Handle -> PrefixMappings -> IO ()
writePrefixes h pms = mapM_ (writePrefix h) (toPMList pms) >> hPutChar h '\n'

writePrefix :: Handle -> (T.Text, T.Text) -> IO ()
writePrefix h (pre, uri) =
  hPutStr h "@prefix " >> T.hPutStr h pre >> hPutStr h ": " >>
  hPutChar h '<' >> T.hPutStr h uri >> hPutStr h "> ." >> hPutChar h '\n'

writeTriples :: Handle -> Maybe T.Text -> PrefixMappings -> Triples -> IO ()
writeTriples h mdUrl (PrefixMappings pms) ts =
  mapM_ (writeSubjGroup h mdUrl revPms) (groupBy equalSubjects ts)
  where
    revPms = Map.fromList $ map (\(k,v) -> (v,k)) $ Map.toList pms

writeTriple :: Handle -> Maybe T.Text -> PrefixMappings -> Triple -> IO ()
writeTriple h mdUrl (PrefixMappings pms) t = 
  w subjectOf >> space >> w predicateOf >> space >> w objectOf
  where
    w :: (Triple -> Node) -> IO ()
    w f = writeNode h mdUrl (f t) pms
    space = hPutChar h ' '

-- Write a group of triples that all have the same subject, with the subject only
-- being output once, and comma or semi-colon used as appropriate.
writeSubjGroup :: Handle -> Maybe T.Text -> Map T.Text T.Text -> Triples -> IO ()
writeSubjGroup _ _    _   []     = return ()
writeSubjGroup h dUrl pms ts@(t:_) =
  writeNode h dUrl (subjectOf t) pms >> hPutChar h ' ' >>
  writePredGroup h dUrl pms (head ts') >>
  mapM_ (\t' -> hPutStr h ";\n\t" >> writePredGroup h dUrl pms t') (tail ts') >>
  hPutStrLn h " ."
  where
    ts' = groupBy equalPredicates ts

-- Write a group of triples that all have the same subject and the same predicate,
-- assuming the subject has already been output and only the predicate and objects
-- need to be written.
writePredGroup :: Handle -> Maybe T.Text -> Map T.Text T.Text -> Triples -> IO ()
writePredGroup _  _       _   []     = return ()
writePredGroup h  docUrl pms (t:ts) =
  -- The doesn't rule out <> in either the predicate or object (as well as subject), 
  -- so we pass the docUrl through to writeNode in all cases.
  writeNode h docUrl (predicateOf t) pms >> hPutChar h ' ' >> 
  writeNode h docUrl (objectOf t) pms >>
  mapM_ (\t' -> hPutStr h ", " >> writeNode h docUrl (objectOf t') pms) ts

writeNode :: Handle -> Maybe T.Text -> Node -> Map T.Text T.Text -> IO ()
writeNode h mdUrl node prefixes =
  case node of
    (UNode bs)  -> let currUri = bs
                   in case mdUrl of
                        Nothing  -> writeUNodeUri h currUri prefixes
                        Just url -> if url == currUri then hPutStr h "<>" else writeUNodeUri h currUri prefixes
    (BNode gId) -> T.hPutStr h gId
    (BNodeGen i)-> putStr "_:genid" >> hPutStr h (show i)
    (LNode n)   -> writeLValue h n prefixes

writeUNodeUri :: Handle -> T.Text -> Map T.Text T.Text -> IO ()
writeUNodeUri h uri prefixes =
  case mapping of
    Nothing                 -> hPutChar h '<' >> T.hPutStr h uri >> hPutChar h '>'
    (Just (pre, localName)) -> T.hPutStr h pre >> hPutChar h ':' >> T.hPutStr h localName
  where
    mapping         = findMapping prefixes uri

-- Print prefix mappings to stdout for debugging.
_debugPMs     :: Map T.Text T.Text -> IO ()
_debugPMs pms =  mapM_ (\(k, v) -> T.putStr k >> putStr "__" >> T.putStrLn v) (Map.toList pms)

-- Expects a map from uri to prefix, and returns the (prefix, uri_expansion)
-- from the mappings such that uri_expansion is a prefix of uri, or Nothing if
-- there is no such mapping. This function does a linear-time search over the 
-- map, but the prefix mappings should always be very small, so it's okay for now.
findMapping :: Map T.Text T.Text -> T.Text -> Maybe (T.Text, T.Text)
findMapping pms uri =
  case mapping of
    Nothing     -> Nothing
    Just (u, p) -> Just (p, T.drop (T.length u) uri) -- empty localName is permitted
  where
    mapping        = find (\(k, _) -> T.isPrefixOf k uri) (Map.toList pms)

writeLValue :: Handle -> LValue -> Map T.Text T.Text -> IO ()
writeLValue h lv pms =
  case lv of
    (PlainL lit)       -> writeLiteralString h lit
    (PlainLL lit lang) -> writeLiteralString h lit >>
                            hPutStr h "@" >>
                            T.hPutStr h lang
    (TypedL lit dtype) -> writeLiteralString h lit >>
                            hPutStr h "^^" >>
                            writeUNodeUri h dtype pms
                            -- writeUNodeUri h (T.reverse dtype) pms

writeLiteralString:: Handle -> T.Text -> IO ()
writeLiteralString h bs =
  do hPutChar h '"'
     T.foldl' writeChar (return True) bs
     hPutChar h '"'
  where
    writeChar :: IO Bool -> Char -> IO Bool
    writeChar b c =
      case c of
        '\n' ->  b >>= \b' -> when b' (hPutChar h '\\' >> hPutChar h 'n')  >> return True
        '\t' ->  b >>= \b' -> when b' (hPutChar h '\\' >> hPutChar h 't')  >> return True
        '\r' ->  b >>= \b' -> when b' (hPutChar h '\\' >> hPutChar h 'r')  >> return True
        '"'  ->  b >>= \b' -> when b' (hPutChar h '\\' >> hPutChar h '"')  >> return True
        '\\' ->  b >>= \b' -> when b' (hPutChar h '\\' >> hPutChar h '\\') >> return True
        _    ->  b >>= \b' -> when b' (hPutChar  h c)                      >> return True