{-# LANGUAGE MultiWayIf        #-}
{-# LANGUAGE OverloadedStrings #-}

-- | Paths are horrible, so they have their own module now.
-- I just hope you are running this on some kind of Unix
module Paths where

import           Data.Text             (Text, isPrefixOf)
import qualified Data.Text             as T
import           System.FilePath       (splitPath)
import           System.FilePath.Posix ((</>))
import           Text.Regex.TDFA
import           Util                  (PrettyPrint (prettyprint))

-- | a normalised path: a number of "upwards" steps, and
-- a path without any . or .. in it. Also possibly a
-- fragment, mostly for map links.
data RelPath = Path Int Text (Maybe Text)
  deriving (Show, Eq, Ord)



data PathResult = OkRelPath RelPath | AbsolutePath | NotAPath | UnderscoreMapLink | AtMapLink

-- | horrible regex parsing for filepaths that is hopefully kinda safe
parsePath :: Text -> PathResult
parsePath text =
  if | rest =~ ("^([^/]*[^\\./]/)*[^/]*[^\\./]$" :: Text) -> OkRelPath (Path up path fragment)
     | "/_/" `isPrefixOf` text ->  UnderscoreMapLink
     | "/@/" `isPrefixOf` text ->  AtMapLink
     | "/" `isPrefixOf` text ->  AbsolutePath
     | otherwise ->  NotAPath
  where
    (_, prefix, rest, _) =
      text =~ ("^((\\.|\\.\\.)/)*" :: Text) :: (Text, Text, Text, [Text])
    -- how many steps upwards in the tree?
    up = length . filter (".." ==) . T.splitOn  "/" $ prefix
    parts = T.splitOn "#" rest
    path = head parts
    fragment = if length parts >= 2
      then Just $ T.concat $ tail parts -- TODO!
      else Nothing

instance PrettyPrint RelPath where
  prettyprint (Path up rest frag) = ups <> rest <> fragment
    where ups = T.concat $ replicate up "../"
          fragment = maybe mempty ("#" <>) frag

-- | Normalises a path.
--
-- It takes a `prefix`, and will "truncate" the .. operator
-- at the end of the prefix, i.e. it will never return paths
-- that lie (naïvely) outside of the prefix.
normalise :: FilePath -> RelPath ->  FilePath
normalise prefix (Path 0 path _) = prefix </> T.unpack path
normalise prefix (Path i path _) =
  concat (take (length dirs - i) dirs) </> T.unpack path
  where dirs = splitPath prefix

normaliseWithFrag :: FilePath -> RelPath -> FilePath
normaliseWithFrag prefix (Path i path frag) =
  normalise prefix (Path (i+1) path frag) <> T.unpack (maybe mempty ("#" <>) frag)