-- |
-- Module      :  Path
-- Copyright   :  © 2015–2016 FP Complete
-- License     :  BSD 3 clause
--
-- Maintainer  :  Chris Done <chrisdone@fpcomplete.com>
-- Stability   :  experimental
-- Portability :  portable
--
-- Support for well-typed paths.

{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE DeriveDataTypeable #-}
{-# LANGUAGE EmptyDataDecls #-}
{-# LANGUAGE FlexibleInstances #-}

module Path
  (-- * Types
   Path
  ,Abs
  ,Rel
  ,File
  ,Dir
   -- * Parsing
  ,parseAbsDir
  ,parseRelDir
  ,parseAbsFile
  ,parseRelFile
  ,PathParseException
  -- * Constructors
  ,mkAbsDir
  ,mkRelDir
  ,mkAbsFile
  ,mkRelFile
  -- * Operations
  ,(</>)
  ,stripDir
  ,isParentOf
  ,parent
  ,filename
  ,dirname
  -- * Conversion
  ,toFilePath
  ,fromAbsDir
  ,fromRelDir
  ,fromAbsFile
  ,fromRelFile
  )
  where

import           Control.Exception (Exception)
import           Control.Monad.Catch (MonadThrow(..))
import           Data.Aeson (FromJSON (..))
import qualified Data.Aeson.Types as Aeson
import           Data.Data
import           Data.List
import           Data.Maybe
import           Language.Haskell.TH
import           Path.Internal
import qualified System.FilePath as FilePath

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

-- | An absolute path.
data Abs deriving (Typeable)

-- | A relative path; one without a root.
data Rel deriving (Typeable)

-- | A file path.
data File deriving (Typeable)

-- | A directory path.
data Dir deriving (Typeable)

instance FromJSON (Path Abs File) where
  parseJSON = parseJSONWith parseAbsFile
  {-# INLINE parseJSON #-}

instance FromJSON (Path Rel File) where
  parseJSON = parseJSONWith parseRelFile
  {-# INLINE parseJSON #-}

instance FromJSON (Path Abs Dir) where
  parseJSON = parseJSONWith parseAbsDir
  {-# INLINE parseJSON #-}

instance FromJSON (Path Rel Dir) where
  parseJSON = parseJSONWith parseRelDir
  {-# INLINE parseJSON #-}

parseJSONWith :: (Show e, FromJSON a)
              => (a -> Either e b) -> Aeson.Value -> Aeson.Parser b
parseJSONWith f x =
  do fp <- parseJSON x
     case f fp of
       Right p -> return p
       Left e -> fail (show e)
{-# INLINE parseJSONWith #-}

-- | Exception when parsing a location.
data PathParseException
  = InvalidAbsDir FilePath
  | InvalidRelDir FilePath
  | InvalidAbsFile FilePath
  | InvalidRelFile FilePath
  | Couldn'tStripPrefixDir FilePath FilePath
  deriving (Show,Typeable)
instance Exception PathParseException

--------------------------------------------------------------------------------
-- Parsers

-- | Get a location for an absolute directory. Produces a normalized
--  path which always ends in a path separator.
--
-- Throws: 'PathParseException'
--
parseAbsDir :: MonadThrow m
            => FilePath -> m (Path Abs Dir)
parseAbsDir filepath =
  if FilePath.isAbsolute filepath &&
     not (null (normalizeDir filepath)) &&
     not ("~/" `isPrefixOf` filepath) &&
     not (hasParentDir filepath) &&
     FilePath.isValid filepath
     then return (Path (normalizeDir filepath))
     else throwM (InvalidAbsDir filepath)

-- | Get a location for a relative directory. Produces a normalized
-- path which always ends in a path separator.
--
-- Note that @filepath@ may contain any number of @./@ but may not consist solely of @./@.  It also may not contain a single @..@ anywhere.
--
-- Throws: 'PathParseException'
--
parseRelDir :: MonadThrow m
            => FilePath -> m (Path Rel Dir)
parseRelDir filepath =
  if not (FilePath.isAbsolute filepath) &&
     not (null filepath) &&
     not ("~/" `isPrefixOf` filepath) &&
     not (hasParentDir filepath) &&
     not (null (normalizeDir filepath)) &&
     filepath /= "." && filepath /= ".." &&
     FilePath.isValid filepath
     then return (Path (normalizeDir filepath))
     else throwM (InvalidRelDir filepath)

-- | Get a location for an absolute file.
--
-- Throws: 'PathParseException'
--
parseAbsFile :: MonadThrow m
             => FilePath -> m (Path Abs File)
parseAbsFile filepath =
  if FilePath.isAbsolute filepath &&
     not (FilePath.hasTrailingPathSeparator filepath) &&
     not ("~/" `isPrefixOf` filepath) &&
     not (hasParentDir filepath) &&
     not (null (normalizeFile filepath)) &&
     FilePath.isValid filepath
     then return (Path (normalizeFile filepath))
     else throwM (InvalidAbsFile filepath)

-- | Get a location for a relative file.
--
-- Note that @filepath@ may contain any number of @./@ but may not contain a single @..@ anywhere.
--
-- Throws: 'PathParseException'
--
parseRelFile :: MonadThrow m
             => FilePath -> m (Path Rel File)
parseRelFile filepath =
  if not (FilePath.isAbsolute filepath ||
          FilePath.hasTrailingPathSeparator filepath) &&
     not (null filepath) &&
     not ("~/" `isPrefixOf` filepath) &&
     not (hasParentDir filepath) &&
     not (null (normalizeFile filepath)) &&
     filepath /= "." && filepath /= ".." &&
     FilePath.isValid filepath
     then return (Path (normalizeFile filepath))
     else throwM (InvalidRelFile filepath)

-- | Helper function: check if the filepath has any parent directories in it.
-- This handles the logic of checking for different path separators on Windows.
hasParentDir :: FilePath -> Bool
hasParentDir filepath' =
     ("/.." `isSuffixOf` filepath) ||
     ("/../" `isInfixOf` filepath) ||
     ("../" `isPrefixOf` filepath)
  where
    filepath =
        case FilePath.pathSeparator of
            '/' -> filepath'
            x   -> map (\y -> if x == y then '/' else y) filepath'

--------------------------------------------------------------------------------
-- Constructors

-- | Make a 'Path Abs Dir'.
--
-- Remember: due to the nature of absolute paths this (e.g. @\/home\/foo@)
-- may compile on your platform, but it may not compile on another
-- platform (Windows).
mkAbsDir :: FilePath -> Q Exp
mkAbsDir s =
  case parseAbsDir s of
    Left err -> error (show err)
    Right (Path str) ->
      [|Path $(return (LitE (StringL str))) :: Path Abs Dir|]

-- | Make a 'Path Rel Dir'.
mkRelDir :: FilePath -> Q Exp
mkRelDir s =
  case parseRelDir s of
    Left err -> error (show err)
    Right (Path str) ->
      [|Path $(return (LitE (StringL str))) :: Path Rel Dir|]

-- | Make a 'Path Abs File'.
--
-- Remember: due to the nature of absolute paths this (e.g. @\/home\/foo@)
-- may compile on your platform, but it may not compile on another
-- platform (Windows).
mkAbsFile :: FilePath -> Q Exp
mkAbsFile s =
  case parseAbsFile s of
    Left err -> error (show err)
    Right (Path str) ->
      [|Path $(return (LitE (StringL str))) :: Path Abs File|]

-- | Make a 'Path Rel File'.
mkRelFile :: FilePath -> Q Exp
mkRelFile s =
  case parseRelFile s of
    Left err -> error (show err)
    Right (Path str) ->
      [|Path $(return (LitE (StringL str))) :: Path Rel File|]

--------------------------------------------------------------------------------
-- Conversion

-- | Convert to a 'FilePath' type.
--
-- All directories have a trailing slash, so if you want no trailing
-- slash, you can use 'System.FilePath.dropTrailingPathSeparator' from
-- the filepath package.
toFilePath :: Path b t -> FilePath
toFilePath (Path l) = l

-- | Convert absolute path to directory to 'FilePath' type.
fromAbsDir :: Path Abs Dir -> FilePath
fromAbsDir = toFilePath

-- | Convert relative path to directory to 'FilePath' type.
fromRelDir :: Path Rel Dir -> FilePath
fromRelDir = toFilePath

-- | Convert absolute path to file to 'FilePath' type.
fromAbsFile :: Path Abs File -> FilePath
fromAbsFile = toFilePath

-- | Convert relative path to file to 'FilePath' type.
fromRelFile :: Path Rel File -> FilePath
fromRelFile = toFilePath

--------------------------------------------------------------------------------
-- Operations

-- | Append two paths.
--
-- The following cases are valid and the equalities hold:
--
-- @$(mkAbsDir x) \<\/> $(mkRelDir y) = $(mkAbsDir (x ++ \"/\" ++ y))@
--
-- @$(mkAbsDir x) \<\/> $(mkRelFile y) = $(mkAbsFile (x ++ \"/\" ++ y))@
--
-- @$(mkRelDir x) \<\/> $(mkRelDir y) = $(mkRelDir (x ++ \"/\" ++ y))@
--
-- @$(mkRelDir x) \<\/> $(mkRelFile y) = $(mkRelFile (x ++ \"/\" ++ y))@
--
-- The following are proven not possible to express:
--
-- @$(mkAbsFile …) \<\/> x@
--
-- @$(mkRelFile …) \<\/> x@
--
-- @x \<\/> $(mkAbsFile …)@
--
-- @x \<\/> $(mkAbsDir …)@
--
(</>) :: Path b Dir -> Path Rel t -> Path b t
(</>) (Path a) (Path b) = Path (a ++ b)

-- | Strip directory from path, making it relative to that directory.
-- Throws 'Couldn'tStripPrefixDir' if directory is not a parent of the path.
--
-- The following properties hold:
--
-- @stripDir x (x \<\/> y) = y@
--
-- Cases which are proven not possible:
--
-- @stripDir (a :: Path Abs …) (b :: Path Rel …)@
--
-- @stripDir (a :: Path Rel …) (b :: Path Abs …)@
--
-- In other words the bases must match.
--
stripDir :: MonadThrow m
         => Path b Dir -> Path b t -> m (Path Rel t)
stripDir (Path p) (Path l) =
  case stripPrefix p l of
    Nothing -> throwM (Couldn'tStripPrefixDir p l)
    Just "" -> throwM (Couldn'tStripPrefixDir p l)
    Just ok -> return (Path ok)

-- | Is p a parent of the given location? Implemented in terms of
-- 'stripDir'. The bases must match.
isParentOf :: Path b Dir -> Path b t -> Bool
isParentOf p l =
  isJust (stripDir p l)

-- | Take the absolute parent directory from the absolute path.
--
-- The following properties hold:
--
-- @parent (x \<\/> y) == x@
--
-- On the root, getting the parent is idempotent:
--
-- @parent (parent \"\/\") = \"\/\"@
--
parent :: Path Abs t -> Path Abs Dir
parent (Path fp) =
  Path (normalizeDir (FilePath.takeDirectory (FilePath.dropTrailingPathSeparator fp)))

-- | Extract the file part of a path.
--
-- The following properties hold:
--
-- @filename (p \<\/> a) == filename a@
--
filename :: Path b File -> Path Rel File
filename (Path l) =
  Path (normalizeFile (FilePath.takeFileName l))

-- | Extract the last directory name of a path.
--
-- The following properties hold:
--
-- @dirname (p \<\/> a) == dirname a@
--
dirname :: Path b Dir -> Path Rel Dir
dirname (Path l) =
  Path (last (FilePath.splitPath l))

--------------------------------------------------------------------------------
-- Internal functions

-- | Internal use for normalizing a directory.
normalizeDir :: FilePath -> FilePath
normalizeDir =
  clean . FilePath.addTrailingPathSeparator . FilePath.normalise
  where clean "./" = ""
        clean ('/':'/':xs) = clean ('/':xs)
        clean x = x

-- | Internal use for normalizing a fileectory.
normalizeFile :: FilePath -> FilePath
normalizeFile =
  clean . FilePath.normalise
  where clean "./" = ""
        clean ('/':'/':xs) = clean ('/':xs)
        clean x = x