-- LANGUAGE pragmas need to go in System.Path.[Windows|Posix]
module System.Path.MODULE_NAME
(
  -- * The main filepath (& dirpath) abstract type
  Path, -- kept abstract

  -- * Phantom Types
  Abs,
  Rel,
  File,
  Dir,

  -- * Type Synonyms
  AbsFile,
  RelFile,
  AbsDir,
  RelDir,
  AbsPath,
  RelPath,
  FilePath,
  DirPath,

  -- * Classes
  AbsRelClass(..),
  FileDirClass(..),

  -- * Path to String conversion
  getPathString,

  -- * Constants
  rootDir,
  currentDir,

  -- * Unchecked Construction Functions
  asPath,
  asRelFile,
  asRelDir,
  asAbsFile,
  asAbsDir,
  asRelPath,
  asAbsPath,
  asFilePath,
  asDirPath,

  -- * Checked Construction Functions
  mkPathAbsOrRel,
  mkPathFileOrDir,
  mkAbsPath,
  mkAbsPathFromCwd,

  -- * Basic Manipulation Functions
  (</>),
  (<.>),
  addExtension,
  combine,
  dropExtension,
  dropExtensions,
  dropFileName,
  replaceExtension,
  replaceBaseName,
  replaceDirectory,
  replaceFileName,
  splitExtension,
  splitExtensions,
  splitFileName,
  takeBaseName,
  takeDirectory,
  takeExtension,
  takeExtensions,
  takeFileName,

  -- * Auxillary Manipulation Functions
  equalFilePath,
  joinPath,
  normalise,
  splitPath,
  makeRelative,
  makeAbsolute,
  makeAbsoluteFromCwd,
  genericMakeAbsolute,
  genericMakeAbsoluteFromCwd,
  pathMap,

  -- * Path Predicates
  isAbsolute,
  isAbsoluteString,
  isRelative,
  isRelativeString,
  hasAnExtension,
  hasExtension,

  -- * Separators
  addTrailingPathSeparator,
  dropTrailingPathSeparator,
  extSeparator,
  hasTrailingPathSeparator,
  pathSeparator,
  pathSeparators,
  searchPathSeparator,
  isExtSeparator,
  isPathSeparator,
  isSearchPathSeparator,

  -- * Generic Manipulation Functions
  genericAddExtension,
  genericDropExtension,
  genericDropExtensions,
  genericSplitExtension,
  genericSplitExtensions,
  genericTakeExtension,
  genericTakeExtensions
)

where

import qualified System.Directory as SD

import Control.Arrow (first, (|||), (***))
import Control.Applicative ((<$>))
import Control.DeepSeq (NFData(rnf))
import Data.List (isSuffixOf, isPrefixOf, stripPrefix, intercalate)
import Data.String (IsString(fromString))
import Data.Char (isSpace)

import Text.Printf (printf)

import qualified Test.QuickCheck as QC
import Test.QuickCheck
          (Gen, Property, property, Arbitrary(arbitrary),
           oneof, frequency, quickCheck)

import Prelude hiding (FilePath)


------------------------------------------------------------------------
-- Types

data Abs
data Rel
data File
data Dir

-- | This is the main filepath abstract datatype
data Path ar fd = PathRoot -- ^ Invariant - this should always have type :: DirPath ar
                | FileDir !(DirPath ar) !PathComponent -- The fact that we recurse binding fd to Dir
                                                       -- makes this a "nested datatype"
                  deriving (Eq, Ord)

-- Possible GADT version...
--
-- data Path ar fd where
--   AbsRoot :: Path Abs Dir
--   RelRoot :: Path Rel Dir
--   File    :: Path ar Dir -> PathComponent -> Path ar File
--   Dir     :: Path ar Dir -> PathComponent -> Path ar Dir
--
-- ... doesn't presently seem to add much value over non-GADT.

newtype PathComponent = PathComponent String deriving (Eq,Ord)

type AbsFile = Path Abs File
type RelFile = Path Rel File
type AbsDir  = Path Abs Dir
type RelDir  = Path Rel Dir

type AbsPath  fd = Path Abs fd
type RelPath  fd = Path Rel fd
type FilePath ar = Path ar File
type DirPath  ar = Path ar Dir

instance NFData PathComponent where
    rnf (PathComponent pc) = rnf pc

instance NFData (Path ar fd) where
    rnf PathRoot = ()
    rnf (FileDir d pc) = rnf (d, pc)

-- I don't think this basic type of fold is appropriate for a nested datatype
-- pathFold :: a -> (a -> String -> a) -> Path ar fd -> a
-- pathFold pr f PathRoot = pr
-- pathFold pr f (FileDir d pc) = f (pathFold pr f d) (unPathComponent pc)

-- | Map over the components of the path.
--
-- >> pathMap (map toLower) "/tmp/Reports/SpreadSheets" == "/tmp/reports/spreadsheets"
pathMap :: (String -> String) -> Path ar fd -> Path ar fd
pathMap _ PathRoot = PathRoot
pathMap f (FileDir d pc) = FileDir (pathMap f d) (pcMap f pc)

-- Private fn
pcMap :: (String -> String) -> PathComponent -> PathComponent
pcMap f (PathComponent s) = PathComponent (f s)


------------------------------------------------------------------------
-- Type classes and machinery for switching on Abs/Rel and File/Dir

-- | This class provides a way to prevent other modules
--   from making further 'AbsRelClass' or 'FileDirClass'
--   instances
class Private p
instance Private Abs
instance Private Rel
instance Private File
instance Private Dir

-- | This class allows selective behaviour for absolute and
--   relative paths and is mostly for internal use.
class Private ar => AbsRelClass ar where
    -- | See <https://wiki.haskell.org/Closed_world_instances>
    --   for the used technique.
    switchAbsRel :: f Abs -> f Rel -> f ar
    -- | Will become a top-level function in future
    absRel :: (AbsPath fd -> a) -> (RelPath fd -> a) -> Path ar fd -> a
    absRel f g = runAbsRel $ switchAbsRel (AbsRel f) (AbsRel g)

newtype AbsRel fd a ar = AbsRel {runAbsRel :: Path ar fd -> a}

instance AbsRelClass Abs where switchAbsRel f _g = f
instance AbsRelClass Rel where switchAbsRel _f g = g

-- | This class allows selective behaviour for file and
--   directory paths and is mostly for internal use.
class Private fd => FileDirClass fd where
    switchFileDir :: f File -> f Dir -> f fd
    -- | Will become a top-level function in future
    fileDir :: (FilePath ar -> a) -> (DirPath ar -> a) -> Path ar fd -> a
    fileDir f g = runFileDir $ switchFileDir (FileDirFunc f) (FileDirFunc g)

newtype FileDir ar a fd = FileDirFunc {runFileDir :: Path ar fd -> a}

instance FileDirClass File where switchFileDir f _g = f
instance FileDirClass Dir  where switchFileDir _f g = g


-- | Currently not exported
_pathAbsRel :: AbsRelClass ar => Path ar fd -> Either (AbsPath fd) (RelPath fd)
_pathAbsRel = absRel Left Right

-- | Currently not exported
_pathFileDir :: FileDirClass fd => Path ar fd -> Either (FilePath ar) (DirPath ar)
_pathFileDir = fileDir Left Right

------------------------------------------------------------------------
-- Read & Show instances

-- >> show (rootDir </> "bla" </> "blub") == "rootDir </> \"bla\" </> \"blub\""
-- >> show (Just (rootDir </> "bla" </> "blub")) == "Just (rootDir </> \"bla\" </> \"blub\")"
-- >> show (currentDir </> "bla" </> "blub") == "currentDir </> \"bla\" </> \"blub\""
-- >> show (Just (currentDir </> "bla" </> "blub")) == "Just (currentDir </> \"bla\" </> \"blub\")"
instance AbsRelClass ar => Show (Path ar fd) where
    showsPrec d =
        let go :: AbsRelClass ar => Path ar fd -> ShowS
            go x@PathRoot =
                absRel (const $ showString rootName) (const $ showString currentName) x
            go (FileDir p (PathComponent pc)) =
                go p . showChar ' ' .
                showString combineOperator . showChar ' ' . shows pc
        in  showParen (d>9) . go

-- >> read (show (rootDir </> "bla" </> "blub")) == rootDir </> "bla" </> "blub"
-- >> read (show (Just (rootDir </> "bla" </> "blub"))) == Just (rootDir </> "bla" </> "blub")
-- >> read (show (currentDir </> "bla" </> "blub")) == currentDir </> "bla" </> "blub"
-- >> read (show (Just (currentDir </> "bla" </> "blub"))) == Just (currentDir </> "bla" </> "blub")
instance AbsRelClass ar => Read (Path ar fd) where
    readsPrec d = readParen (d>9) $ \str ->
        let go :: AbsRelClass ar => Path ar Dir -> ReadS (Path ar fd)
            go path s0 =
                case stripPrefix combineOperator $ dropWhile isSpace s0 of
                    Nothing -> [(relaxDir path, s0)]
                    Just s1 -> do
                        (pc, s2) <- reads s1
                        go (FileDir path (PathComponent pc)) s2
            result = do
                let required = absRel (const rootName) (const currentName) $ fst $ head result
                maybe [] (go PathRoot) $
                    stripPrefix required $ dropWhile isSpace str
        in  result

relaxDir :: Path ar Dir -> Path ar fd
relaxDir PathRoot = PathRoot
relaxDir (FileDir p pc) = FileDir p pc

-- | Convert the 'Path' into a plain 'String' as required for OS calls.
getPathString :: AbsRelClass ar => Path ar fd -> String
getPathString = flip getPathStringS ""

getPathStringS :: AbsRelClass ar => Path ar fd -> ShowS
getPathStringS =
    let go :: AbsRelClass ar => Path ar fd -> ShowS
        go x@PathRoot =
            absRel
                (const $ showChar pathSeparator)
                (const $ showString currentDirComponent) x
        -- we need the clause below so that we don't duplicate the pathSeparator after an abs
        -- root and we don't want to display a "./" prefix on relative paths
        go (FileDir p@PathRoot (PathComponent pc)) =
            absRel (const $ showChar pathSeparator) (const id) p .
            showString pc
        go (FileDir p (PathComponent pc)) =
            go p . showChar pathSeparator . showString pc
    in  go

prop_asPath_getPathString :: AbsFile -> Property
prop_asPath_getPathString p = property $ p == asPath (getPathString p)


------------------------------------------------------------------------
-- Windows / Posix

_isPosix :: Bool
_isPosix = not isWindows

isWindows :: Bool
isWindows = IS_WINDOWS

------------------------------------------------------------------------
-- Constants

rootDir :: AbsDir
rootDir = PathRoot

currentDir :: RelDir
currentDir = PathRoot

rootName :: String
rootName = "rootDir"

currentName :: String
currentName = "currentDir"

currentDirComponent :: String
currentDirComponent = "."


------------------------------------------------------------------------
-- Unchecked Construction Functions
-- NB - these construction functions are non-IO and do no checking!!

-- | Use a 'String' as a 'Path' whose type is determined
--   by its context.
--
-- >> asPath "/tmp" == "/tmp"
-- >> asPath "file.txt" == "file.txt"
-- >> isAbsolute (asPath "/tmp" :: AbsDir) == True
-- >> isAbsolute (asPath "/tmp" :: RelDir) == False
-- >> getPathString (asPath "/tmp" :: AbsDir) == "/tmp"
-- >> getPathString (asPath "/tmp" :: RelDir) == "tmp"
asPath :: String -> Path ar fd
asPath = mkPathFromComponents . mkPathComponents

-- | Use a 'String' as a 'RelFile'. No checking is done.
--
-- >> getPathString (asRelFile "file.txt") == "file.txt"
-- >> getPathString (asRelFile "/file.txt") == "file.txt"
-- >> getPathString (asRelFile "tmp") == "tmp"
-- >> getPathString (asRelFile "/tmp") == "tmp"
asRelFile :: String -> RelFile
asRelFile = asPath

-- | Use a 'String' as a 'RelDir'. No checking is done.
--
-- >> getPathString (asRelDir ".") == "."
-- >> getPathString (asRelDir "file.txt") == "file.txt"
-- >> getPathString (asRelDir "/file.txt") == "file.txt"
-- >> getPathString (asRelDir "tmp") == "tmp"
-- >> getPathString (asRelDir "/tmp") == "tmp"
asRelDir :: String -> RelDir
asRelDir = asPath

-- | Use a 'String' as an 'AbsFile'. No checking is done.
--
-- >> getPathString (asAbsFile "file.txt") == "/file.txt"
-- >> getPathString (asAbsFile "/file.txt") == "/file.txt"
-- >> getPathString (asAbsFile "tmp") == "/tmp"
-- >> getPathString (asAbsFile "/tmp") == "/tmp"
asAbsFile :: String -> AbsFile
asAbsFile = asPath

-- | Use a 'String' as an 'AbsDir'. No checking is done.
--
-- >> getPathString (asAbsDir "file.txt") == "/file.txt"
-- >> getPathString (asAbsDir "/file.txt") == "/file.txt"
-- >> getPathString (asAbsDir "tmp") == "/tmp"
-- >> getPathString (asAbsDir "/tmp") == "/tmp"
asAbsDir :: String -> AbsDir
asAbsDir = asPath

-- | Use a 'String' as a 'RelPath fd'. No checking is done.
asRelPath :: String -> RelPath fd
asRelPath = asPath

-- | Use a 'String' as an 'AbsPath fd'. No checking is done.
asAbsPath :: String -> AbsPath fd
asAbsPath = asPath

-- | Use a 'String' as a 'FilePath ar'. No checking is done.
asFilePath :: String -> FilePath ar
asFilePath = asPath

-- | Use a 'String' as a 'DirPath ar'. No checking is done.
asDirPath :: String -> DirPath ar
asDirPath = asPath

-- | Allow use of OverloadedStrings if desired
instance IsString (Path ar fd) where fromString = asPath

------------------------------------------------------------------------
-- Checked Construction Functions

-- | Examines the supplied string and constructs an absolute or
-- relative path as appropriate.
--
-- >> mkPathAbsOrRel "/tmp" == Left (asAbsDir "/tmp")
-- >> mkPathAbsOrRel  "tmp" == Right (asRelDir "tmp")
mkPathAbsOrRel :: String -> Either (AbsPath fd) (RelPath fd)
mkPathAbsOrRel s =
    if isAbsoluteString s
      then Left $ asAbsPath s
      else Right $ asRelPath s

-- | Searches for a file or directory with the supplied path string
--   and returns a 'File' or 'Dir' path as appropriate. If neither exists
--   at the supplied path, 'Nothing' is returned.
mkPathFileOrDir ::
    AbsRelClass ar => String -> IO (Maybe (Either (FilePath ar) (DirPath ar)))
mkPathFileOrDir s = do
  isfile <- SD.doesFileExist s
  isdir <- SD.doesDirectoryExist s
  case (isfile, isdir) of
    (False, False) -> return Nothing
    (True,  False) -> return $ Just $ Left $ asPath s
    (False, True ) -> return $ Just $ Right $ asPath s
    (True,  True ) -> ioError $ userError "mkPathFileOrDir - object type changed while checking"

-- | Convert a 'String' into an 'AbsPath' by interpreting it as
--   relative to the supplied directory if necessary.
--
-- >> mkAbsPath "/tmp" "foo.txt" == "/tmp/foo.txt"
-- >> mkAbsPath "/tmp" "/etc/foo.txt" == "/etc/foo.txt"
mkAbsPath :: AbsDir -> String -> AbsPath fd
mkAbsPath d = (id ||| makeAbsolute d) . mkPathAbsOrRel

-- | Convert a 'String' into an 'AbsPath' by interpreting it as
--   relative to the cwd if necessary.
mkAbsPathFromCwd :: String -> IO (AbsPath fd)
mkAbsPathFromCwd = (return ||| makeAbsoluteFromCwd) . mkPathAbsOrRel


------------------------------------------------------------------------
-- Internal Functions for PathComponent manipulation

mkPathFromComponents :: [PathComponent] -> Path ar fd
mkPathFromComponents pcs =
    case reverse pcs of
      [] -> PathRoot
      p:ps -> FileDir (foldr (flip FileDir) PathRoot ps) p

mkPathComponents :: String -> [PathComponent]
mkPathComponents xs =
    case break isPathSeparator (dropWhile isPathSeparator xs) of
      ("","")  -> []
      (s,rest) -> PathComponent s : mkPathComponents rest

pathComponents :: Path ar fd -> [PathComponent]
pathComponents PathRoot = []
pathComponents (FileDir p pc) = pathComponents p ++ [pc]

prop_mkPathFromComponents_pathComponents :: AbsFile -> Property
prop_mkPathFromComponents_pathComponents p =
    property $ mkPathFromComponents (pathComponents p) == p



------------------------------------------------------------------------
-- Basic Manipulation Functions

combineOperator :: String
combineOperator = "</>"

-- | Infix variant of 'combine'.
(</>) :: DirPath ar -> RelPath fd -> Path ar fd
PathRoot         </> PathRoot       = PathRoot
(FileDir dp dpc) </> PathRoot       = FileDir dp dpc
d                </> (FileDir p pc) = FileDir (d </> p) pc

-- | Infix variant of 'addExtension'.
--   We only allow files (and not directories) to have extensions added
--   by this function. This is because it's the vastly common case and
--   an attempt to add one to a directory will - more often than not -
--   represent an error.
--   We don't however want to prevent the corresponding operation on
--   directories, and so we provide a function that is more flexible:
--   'genericAddExtension'.
(<.>) :: FilePath ar -> String -> FilePath ar
(<.>) = genericAddExtension

-- | Add an extension, even if there is already one there.
--   E.g. @addExtension \"foo.txt\" \"bat\" -> \"foo.txt.bat\"@.
--
-- >> addExtension "file.txt" "bib" == "file.txt.bib"
-- >> addExtension "file." ".bib" == "file..bib"
-- >> addExtension "file" ".bib" == "file.bib"
-- >> addExtension "" "bib" == ".bib"
-- >> addExtension "" ".bib" == ".bib"
-- >> takeFileName (addExtension "" "ext") == ".ext"
addExtension :: FilePath ar -> String -> FilePath ar
addExtension = (<.>)

-- | Join an (absolute or relative) directory path with a relative
--   (file or directory) path to form a new path.
combine :: DirPath ar -> RelPath fd -> Path ar fd
combine = (</>)


-- | Remove last extension, and the \".\" preceding it.
--
-- >> dropExtension x == fst (splitExtension x)
dropExtension :: FilePath ar -> FilePath ar
dropExtension = fst . splitExtension

-- | Drop all extensions
--
-- >> not $ hasAnExtension (dropExtensions x)
dropExtensions :: FilePath ar -> FilePath ar
dropExtensions = fst . splitExtensions

-- | Synonym for 'takeDirectory'
dropFileName :: Path ar fd -> DirPath ar
dropFileName = fst . splitFileName


-- | Set the extension of a file, overwriting one if already present.
--
-- >> replaceExtension "file.txt" ".bob" == "file.bob"
-- >> replaceExtension "file.txt" "bob" == "file.bob"
-- >> replaceExtension "file" ".bob" == "file.bob"
-- >> replaceExtension "file.txt" "" == "file"
-- >> replaceExtension "file.fred.bob" "txt" == "file.fred.txt"
replaceExtension :: FilePath ar -> String -> FilePath ar
replaceExtension p ext = dropExtension p <.> ext

replaceBaseName :: Path ar fd -> String -> Path ar fd
replaceBaseName p bn = takeDirectory p </> (asPath bn `genericAddExtension` genericTakeExtension p)

replaceDirectory :: Path ar1 fd -> DirPath ar2 -> Path ar2 fd
replaceDirectory p d = d </> takeFileName p

replaceFileName :: Path ar fd -> String -> Path ar fd
replaceFileName p fn = takeDirectory p </> asPath fn


-- | Split on the extension. 'addExtension' is the inverse.
--
-- >> uncurry (<.>) (splitExtension x) == x
-- >> uncurry addExtension (splitExtension x) == x
-- >> splitExtension "file.txt" == ("file",".txt")
-- >> splitExtension "file" == ("file","")
-- >> splitExtension "file/file.txt" == ("file/file",".txt")
-- >> splitExtension "file.txt/boris" == ("file.txt/boris","")
-- >> splitExtension "file.txt/boris.ext" == ("file.txt/boris",".ext")
-- >> splitExtension "file/path.txt.bob.fred" == ("file/path.txt.bob",".fred")
splitExtension :: FilePath ar -> (FilePath ar, String)
splitExtension = genericSplitExtension

-- | Split on all extensions
--
-- >> splitExtensions "file.tar.gz" == ("file",".tar.gz")
splitExtensions :: FilePath ar -> (FilePath ar, String)
splitExtensions = genericSplitExtensions

prop_split_combineExt :: AbsFile -> Property
prop_split_combineExt p = property $ p == uncurry (<.>) (splitExtension p)

-- | Path must not be empty
splitFileName :: Path ar fd -> (DirPath ar, RelPath fd)
splitFileName (FileDir p pc) = (p, mkPathFromComponents [pc])
splitFileName PathRoot = error "splitFileName: empty path"

prop_split_combine :: AbsFile -> Property
prop_split_combine p = property $ uncurry combine (splitFileName p) == p


-- | Get the basename of a file
--
-- >> takeBaseName "/tmp/somedir/myfile.txt" == "myfile"
-- >> takeBaseName "./myfile.txt" == "myfile"
-- >> takeBaseName "myfile.txt" == "myfile"
takeBaseName :: Path ar fd -> RelPath fd
takeBaseName = takeFileName . genericDropExtension

takeDirectory :: Path ar fd -> DirPath ar
takeDirectory = fst . splitFileName

-- | Get the extension of a file, returns @\"\"@ for no extension, @.ext@ otherwise.
--
-- >> takeExtension x == snd (splitExtension x)
-- >> takeExtension (addExtension x "ext") == ".ext"
-- >> takeExtension (replaceExtension x "ext") == ".ext"
takeExtension :: FilePath ar -> String
takeExtension = snd . splitExtension

-- | Get all extensions
--
-- >> takeExtensions "file.tar.gz" == ".tar.gz"
takeExtensions :: FilePath ar -> String
takeExtensions = snd . splitExtensions

-- | Get the filename component of a file path (ie stripping all parent dirs)
--
-- >> takeFileName "/tmp/somedir/myfile.txt" == "myfile.txt"
-- >> takeFileName "./myfile.txt" == "myfile.txt"
-- >> takeFileName "myfile.txt" == "myfile.txt"
takeFileName :: Path ar fd -> RelPath fd
takeFileName PathRoot = PathRoot -- becomes a relative root
takeFileName (FileDir _ pc) = FileDir PathRoot pc

prop_takeFileName_end :: AbsFile -> Property
prop_takeFileName_end p = property $ show (takeFileName p) `isSuffixOf` show p


------------------------------------------------------------------------
-- Auxillary Manipulation Functions

-- | Check whether two strings are equal as file paths.
--
-- >> equalFilePath "/tmp/" "/tmp" == True
-- >> equalFilePath "/tmp"  "tmp"  == False
equalFilePath :: String -> String -> Bool
equalFilePath s1 s2 =
    isAbsoluteString s1 == isAbsoluteString s2 && asPath s1 == asPath s2

-- | Constructs a 'Path' from a list of components.
--
-- >> joinPath ["/tmp","someDir","file.txt"] == "/tmp/someDir/file.txt"
-- >> joinPath ["/tmp","someDir","file.txt"] == asRelFile "tmp/someDir/file.txt"
joinPath :: [String] -> Path ar fd
joinPath = asPath . intercalate [pathSeparator]

-- | Currently just transforms:
--
-- >> normalise "/tmp/fred/./jim/./file" == "/tmp/fred/jim/file"
normalise :: Path ar fd -> Path ar fd
normalise =
    mkPathFromComponents .
    filter (/= PathComponent currentDirComponent) .
    pathComponents

-- | Deconstructs a path into its components.
--
-- >> splitPath (asAbsDir "/tmp/someDir/mydir.dir") == (["tmp","someDir","mydir.dir"], Nothing)
-- >> splitPath (asAbsFile "/tmp/someDir/myfile.txt") == (["tmp","someDir"], Just "myfile.txt")
splitPath :: FileDirClass fd => Path ar fd -> ([RelDir], Maybe RelFile)
splitPath PathRoot = ([],Nothing)
splitPath p@(FileDir d pc) =
    first (map (FileDir PathRoot)) $
    fileDir
        (\ _ -> (pathComponents d, Just (FileDir PathRoot pc)))
        (\ _ -> (pathComponents p, Nothing))
        p

-- | This function can be used to construct a relative path by removing
--   the supplied 'AbsDir' from the front. It is a runtime 'error' if the
--   supplied 'AbsPath' doesn't start with the 'AbsDir'.
--
-- >> makeRelative "/tmp/somedir" "/tmp/somedir/anotherdir/file.txt" == asRelFile "anotherdir/file.txt"
-- >> makeRelative "/tmp/somedir" "/tmp/somedir/anotherdir/dir" == asRelDir "anotherdir/dir"
makeRelative :: AbsDir -> AbsPath fd -> RelPath fd
makeRelative relTo orig =
    maybe (error msg) mkPathFromComponents $
    stripPrefix (pathComponents relTo) (pathComponents orig)
  where
    msg =
        printf "System.Path can't make (%s) relative to (%s)"
            (show orig) (show relTo)

-- | Joins an absolute directory with a relative path to construct a
--   new absolute path.
--
-- >> makeAbsolute "/tmp" "file.txt"      == asAbsFile "/tmp/file.txt"
-- >> makeAbsolute "/tmp" "adir/file.txt" == asAbsFile "/tmp/adir/file.txt"
-- >> makeAbsolute "/tmp" "adir/dir"      == asAbsDir "/tmp/adir/dir"
makeAbsolute :: AbsDir -> RelPath fd -> AbsPath fd
makeAbsolute = genericMakeAbsolute

-- | Converts a relative path into an absolute one by
--   prepending the current working directory.
makeAbsoluteFromCwd :: RelPath fd -> IO (AbsPath fd)
makeAbsoluteFromCwd = genericMakeAbsoluteFromCwd

-- | As for 'makeAbsolute', but for use when the path may already be
--   absolute (in which case it is left unchanged).
--
-- >> genericMakeAbsolute "/tmp" (asRelFile "file.txt")       == "/tmp/file.txt"
-- >> genericMakeAbsolute "/tmp" (asRelFile "adir/file.txt")  == "/tmp/adir/file.txt"
-- >> genericMakeAbsolute "/tmp" (asAbsFile "adir/file.txt")  == "/adir/file.txt"
-- >> genericMakeAbsolute "/tmp" (asAbsFile "/adir/file.txt") == "/adir/file.txt"
genericMakeAbsolute :: AbsRelClass ar => AbsDir -> Path ar fd -> AbsPath fd
genericMakeAbsolute base p = absRel id (base </>) p

-- | As for 'makeAbsoluteFromCwd', but for use when the path may already be
--   absolute (in which case it is left unchanged).
genericMakeAbsoluteFromCwd :: AbsRelClass ar => Path ar fd -> IO (AbsPath fd)
genericMakeAbsoluteFromCwd p = do
  cwdString <- SD.getCurrentDirectory -- we don't use System.Path.Directory impl here to avoid module cycle
  return $ genericMakeAbsolute (asAbsDir cwdString) p

prop_makeAbsoluteFromDir_endSame :: AbsDir -> RelFile -> Property
prop_makeAbsoluteFromDir_endSame base p =
    property $ show p `isSuffixOf` show (makeAbsolute base p)

prop_makeAbsoluteFromDir_startSame :: AbsDir -> RelFile -> Property
prop_makeAbsoluteFromDir_startSame base p =
    property $ show base `isPrefixOf` show (makeAbsolute base p)

-- prop_makeAbsoluteFromDir_startSameAbs :: AbsDir -> AbsFile -> Property
-- prop_makeAbsoluteFromDir_startSameAbs base p = property $ show base `isPrefixOf` show (makeAbsolute base p)


------------------------------------------------------------------------
-- NYI - Not Yet Implemented

{-
splitSearchPath  :: String   -> [String]
getSearchPath    :: IO [String]
splitDrive       :: String   -> (String, String)
joinDrive        :: String   -> String -> String
takeDrive        :: String   -> String
hasDrive         :: String   -> Bool
dropDrive        :: String   -> String
isDrive          :: String   -> Bool
isValid          :: String   -> Bool
makeValid        :: String   -> String
-}


------------------------------------------------------------------------
-- Path Predicates

-- | Test whether a @'Path' ar fd@ is absolute.
--
-- >> isAbsolute (asAbsFile "fred")  == True
-- >> isAbsolute (asRelFile "fred")  == False
-- >> isAbsolute (asAbsFile "/fred") == True
-- >> isAbsolute (asRelFile "/fred") == False
isAbsolute :: AbsRelClass ar => Path ar fd -> Bool
isAbsolute = absRel (const True) (const False)

-- | Test whether the 'String' would correspond to an absolute path
--   if interpreted as a 'Path'.
isAbsoluteString :: String -> Bool
isAbsoluteString [] = False -- Treat the empty string as relative because it doesn't start with 'pathSeparators'
isAbsoluteString (x:_) = isPathSeparator x -- Absolute if first char is a path separator

-- | Invariant - this should return True iff arg is of type @'Path' Rel _@
--
-- > isRelative = not . isAbsolute
isRelative :: AbsRelClass ar => Path ar fd -> Bool
isRelative = not . isAbsolute

-- | Test whether the 'String' would correspond to a relative path
--   if interpreted as a 'Path'.
--
-- > isRelativeString = not . isAbsoluteString
isRelativeString :: String -> Bool
isRelativeString = not . isAbsoluteString


-- | Does the given filename have an extension?
--
-- >> null (takeExtension x) == not (hasAnExtension x)
hasAnExtension :: FilePath ar -> Bool
hasAnExtension = not . null . snd . splitExtension

-- | Does the given filename have the given extension?
--
-- >> hasExtension ".hs" "MyCode.hs" == True
-- >> hasExtension ".hs" "MyCode.hs.bak" == False
-- >> hasExtension ".hs" "MyCode.bak.hs" == True
hasExtension :: String -> FilePath ar -> Bool
hasExtension ext = (==ext) . snd . splitExtension


------------------------------------------------------------------------
-- Separators

-- | This is largely for 'System.FilePath' compatability
addTrailingPathSeparator :: String -> String
addTrailingPathSeparator = (++[pathSeparator])

-- | This is largely for 'System.FilePath' compatability
dropTrailingPathSeparator :: String -> String
dropTrailingPathSeparator = init

-- | File extension character
--
-- >> extSeparator == '.'
extSeparator :: Char
extSeparator = '.'

-- | This is largely for 'System.FilePath' compatability
hasTrailingPathSeparator :: String -> Bool
hasTrailingPathSeparator = isPathSeparator . last

-- | The character that separates directories. In the case where more than
--   one character is possible, 'pathSeparator' is the \'ideal\' one.
--
-- >> isPathSeparator pathSeparator
pathSeparator :: Char
pathSeparator | isWindows = '\\'
              | otherwise = '/'

-- | The list of all possible separators.
--
-- >> pathSeparator `elem` pathSeparators
pathSeparators :: [Char]
pathSeparators = return pathSeparator

-- | The character that is used to separate the entries in the $PATH environment variable.
--
searchPathSeparator :: Char
searchPathSeparator = ':'

-- | Is the character an extension character?
--
-- >> isExtSeparator a == (a == extSeparator)
isExtSeparator :: Char -> Bool
isExtSeparator = (== extSeparator)

-- | Rather than using @(== 'pathSeparator')@, use this. Test if something
--   is a path separator.
--
-- >> isPathSeparator a == (a `elem` pathSeparators)
isPathSeparator :: Char -> Bool
isPathSeparator = flip elem pathSeparators

-- | Is the character a file separator?
--
-- >> isSearchPathSeparator a == (a == searchPathSeparator)
isSearchPathSeparator :: Char -> Bool
isSearchPathSeparator = (== searchPathSeparator)


------------------------------------------------------------------------
-- Generic Manipulation Functions

-- These functions support manipulation of extensions on directories
-- as well as files. They have looser types than the corresponding
-- 'Basic Manipulation Functions', but it is expected that the basic
-- functions will be used more frequently as they provide more checks.

-- | This is a more flexible variant of 'addExtension' / '<.>' which can
--   work with files or directories
--
-- >> genericAddExtension "/" "x" == asAbsDir "/.x"
-- >> genericAddExtension "/a" "x" == asAbsDir "/a.x"
-- >> genericAddExtension "" "x" == asRelFile ".x"
-- >> genericAddExtension "" "" == asRelFile ""
genericAddExtension :: Path ar fd -> String -> Path ar fd
genericAddExtension p "" = p
genericAddExtension path ext =
    let suffix =
            if [extSeparator] `isPrefixOf` ext
              then ext
              else extSeparator : ext
    in  case path of
            FileDir p (PathComponent pc) ->
                FileDir p (PathComponent (pc ++ suffix))
            PathRoot ->
                FileDir PathRoot (PathComponent suffix)

genericDropExtension :: Path ar fd -> Path ar fd
genericDropExtension = fst . genericSplitExtension

genericDropExtensions :: Path ar fd -> Path ar fd
genericDropExtensions = fst . genericSplitExtensions

genericSplitExtension :: Path ar fd -> (Path ar fd, String)
genericSplitExtension (FileDir p (PathComponent s)) = (FileDir p (PathComponent s1), s2)
    where (s1,s2) = fixTrailingDot $ rbreak isExtSeparator s
          fixTrailingDot ("",r2) = (r2,"")
          fixTrailingDot (r1,r2) | [extSeparator] `isSuffixOf` r1 = (init r1, extSeparator:r2)
                                 | otherwise = (r1,r2)
          swap (x,y) = (y,x)
          rbreak q = (reverse *** reverse) . swap . break q . reverse
genericSplitExtension p = (p,"")

genericSplitExtensions :: Path ar fd -> (Path ar fd, String)
genericSplitExtensions (FileDir p (PathComponent s)) = (FileDir p (PathComponent s1), s2)
    where (s1,s2) = break isExtSeparator s
genericSplitExtensions p = (p,"")

genericTakeExtension :: Path ar fd -> String
genericTakeExtension = snd . genericSplitExtension

genericTakeExtensions :: Path ar fd -> String
genericTakeExtensions = snd . genericSplitExtension


------------------------------------------------------------------------
-- QuickCheck

_testall :: IO ()
_testall = do
  putStrLn "Running QuickCheck tests..."
  quickCheck prop_asPath_getPathString
  quickCheck prop_mkPathFromComponents_pathComponents
  quickCheck prop_makeAbsoluteFromDir_endSame
  quickCheck prop_makeAbsoluteFromDir_startSame
  quickCheck prop_split_combine
  quickCheck prop_takeFileName_end
  quickCheck prop_split_combineExt
  putStrLn "Tests completed."

-- test :: Testable a => a -> IO ()
-- test = quickCheck

qcFileComponent :: Gen PathComponent
qcFileComponent = PathComponent <$> frequency [
                    (1, return "someFile"),
                    (1, return "fileWith.ext"),
                    (1, return "file.with.multiple.exts"),
                    (1, return "file with spcs")
                  ]

qcDirComponent :: Gen PathComponent
qcDirComponent = PathComponent <$> frequency [
                    (1, return "someDir"),
                    (1, return "aDir"),
                    (1, return "aFolder"),
                    (1, return "a folder"),
                    (1, return "directory")
                  ]

instance Arbitrary PathComponent where
    arbitrary = oneof [qcFileComponent, qcDirComponent]


qcGenPath :: Gen PathComponent -> Gen (Path ar fd)
qcGenPath qcLastComponent = do
    pcs <- QC.listOf qcDirComponent
    pc <- qcLastComponent
    return $ mkPathFromComponents (pcs ++ [pc])

qcFilePath :: Gen (FilePath ar)
qcFilePath = qcGenPath qcFileComponent

qcDirPath :: Gen (DirPath ar)
qcDirPath = qcGenPath qcDirComponent

newtype PathGen ar fd = PathGen {runPathGen :: Gen (Path ar fd)}

qcPath :: (AbsRelClass ar, FileDirClass fd) => Gen (Path ar fd)
qcPath = runPathGen $ switchFileDir (PathGen qcFilePath) (PathGen qcDirPath)

instance (AbsRelClass ar, FileDirClass fd) => Arbitrary (Path ar fd) where
    arbitrary = qcPath