{-# LANGUAGE OverloadedStrings #-}

module Text.RDF.RDF4H.TurtleSerializer.Internal
  ( findMapping
  , writeUNodeUri
  )
where

import           Data.Foldable (fold)
import           Data.List (elemIndex)
import qualified Data.Map as Map
import           Data.Monoid (Any(..), getAny)
import           Data.RDF.Namespace hiding (rdf)
import qualified Data.Text as T
import qualified Data.Text.IO as T
import           System.IO

-- |Converts an aliased URI (e.g., 'rdf:subject') to a tuple whose first element
-- is the full (non-aliased) URI and whose second element is the target/path
-- portion (the part after the colon in the aliased URI).
findMapping :: PrefixMappings -- ^The 'PrefixMappings' to be searched for the prefix that may be a part of the URI.
            -> T.Text         -- ^The URI.
            -> Maybe (T.Text, T.Text)
findMapping (PrefixMappings pms) aliasedURI = do
  (prefix, target) <- splitAliasedURI aliasedURI
  uri <- Map.lookup prefix pms
  pure (uri, target)

-- |Writes the given 'UNode' to the given 'Handle'.
writeUNodeUri :: Handle         -- ^The Handle to write to
              -> T.Text         -- ^The text from a UNode
              -> PrefixMappings -- ^The 'PrefixMappings' which should contain a mapping for any prefix found in the URI.
              -> IO ()
writeUNodeUri h uri _ =
  if (isQName uri)
  then T.hPutStr h uri
  else hPutChar h '<' >> T.hPutStr h uri >> hPutChar h '>'

isQName :: T.Text -> Bool
isQName = not . isFullURI
  where isFullURI :: T.Text -> Bool
        isFullURI = getAny . foldMap (Any .) [ ("http://" `T.isPrefixOf`)
                                             , ("https://" `T.isPrefixOf`)
                                             , ("file://" `T.isPrefixOf`)
                                             ]

-- |Given an aliased URI (e.g., 'rdf:subject') return a tuple whose first
-- element is the alias ('rdf') and whose second part is the path or fragment
-- ('subject').
splitAliasedURI :: T.Text  -- ^Aliased URI.
                -> Maybe (T.Text, T.Text)
splitAliasedURI uri = do
  let uriStr = T.unpack uri
  i <- elemIndex ':' uriStr
  let (prefix, target) = splitAt i uriStr
  pure (T.pack prefix, T.pack $ tail target)