{-# LANGUAGE CPP, ForeignFunctionInterface, ScopedTypeVariables #-}
-----------------------------------------------------------------------------
-- |
-- Module      :  Distribution.Simple.Utils
-- Copyright   :  Isaac Jones, Simon Marlow 2003-2004
-- License     :  BSD3
--                portions Copyright (c) 2007, Galois Inc.
--
-- Maintainer  :  cabal-devel@haskell.org
-- Portability :  portable
--
-- A large and somewhat miscellaneous collection of utility functions used
-- throughout the rest of the Cabal lib and in other tools that use the Cabal
-- lib like @cabal-install@. It has a very simple set of logging actions. It
-- has low level functions for running programs, a bunch of wrappers for
-- various directory and file functions that do extra logging.

module Distribution.Simple.Utils (
        cabalVersion,

        -- * logging and errors
        die,
        dieWithLocation,
        topHandler, topHandlerWith,
        warn, notice, setupMessage, info, debug,
        debugNoWrap, chattyTry,
        printRawCommandAndArgs, printRawCommandAndArgsAndEnv,

        -- * exceptions
        handleDoesNotExist,

        -- * running programs
        rawSystemExit,
        rawSystemExitCode,
        rawSystemExitWithEnv,
        rawSystemStdout,
        rawSystemStdInOut,
        rawSystemIOWithEnv,
        createProcessWithEnv,
        maybeExit,
        xargs,
        findProgramLocation,
        findProgramVersion,

        -- * copying files
        smartCopySources,
        createDirectoryIfMissingVerbose,
        copyFileVerbose,
        copyDirectoryRecursiveVerbose,
        copyFiles,
        copyFileTo,

        -- * installing files
        installOrdinaryFile,
        installExecutableFile,
        installMaybeExecutableFile,
        installOrdinaryFiles,
        installExecutableFiles,
        installMaybeExecutableFiles,
        installDirectoryContents,
        copyDirectoryRecursive,

        -- * File permissions
        doesExecutableExist,
        setFileOrdinary,
        setFileExecutable,

        -- * file names
        currentDir,
        shortRelativePath,
        dropExeExtension,
        exeExtensions,

        -- * finding files
        findFile,
        findFirstFile,
        findFileWithExtension,
        findFileWithExtension',
        findAllFilesWithExtension,
        findModuleFile,
        findModuleFiles,
        getDirectoryContentsRecursive,

        -- * environment variables
        isInSearchPath,
        addLibraryPath,

        -- * simple file globbing
        matchFileGlob,
        matchDirFileGlob,
        parseFileGlob,
        FileGlob(..),

        -- * modification time
        moreRecentFile,
        existsAndIsMoreRecentThan,

        -- * temp files and dirs
        TempFileOptions(..), defaultTempFileOptions,
        withTempFile, withTempFileEx,
        withTempDirectory, withTempDirectoryEx,

        -- * .cabal and .buildinfo files
        defaultPackageDesc,
        findPackageDesc,
        tryFindPackageDesc,
        defaultHookedPackageDesc,
        findHookedPackageDesc,

        -- * reading and writing files safely
        withFileContents,
        writeFileAtomic,
        rewriteFile,

        -- * Unicode
        fromUTF8,
        toUTF8,
        readUTF8File,
        withUTF8FileContents,
        writeUTF8File,
        normaliseLineEndings,

        -- * BOM
        startsWithBOM,
        fileHasBOM,
        ignoreBOM,

        -- * generic utils
        dropWhileEndLE,
        takeWhileEndLE,
        equating,
        comparing,
        isInfixOf,
        intercalate,
        lowercase,
        listUnion,
        listUnionRight,
        ordNub,
        ordNubRight,
        safeTail,
        wrapText,
        wrapLine,
  ) where

import Distribution.Text
import Distribution.Package
import Distribution.ModuleName as ModuleName
import Distribution.System
import Distribution.Version
import Distribution.Compat.CopyFile
import Distribution.Compat.Internal.TempFile
import Distribution.Compat.Exception
import Distribution.Verbosity

#if __GLASGOW_HASKELL__ < 711
#ifdef VERSION_base
#define BOOTSTRAPPED_CABAL 1
#endif
#else
#ifdef CURRENT_PACKAGE_KEY
#define BOOTSTRAPPED_CABAL 1
#endif
#endif

#ifdef BOOTSTRAPPED_CABAL
import qualified Paths_Cabal (version)
#endif

import Control.Monad
    ( when, unless, filterM )
import Control.Concurrent.MVar
    ( newEmptyMVar, putMVar, takeMVar )
import Data.Bits
    ( Bits((.|.), (.&.), shiftL, shiftR) )
import Data.Char as Char
    ( isDigit, toLower, chr, ord )
import Data.Foldable
    ( traverse_ )
import Data.List
    ( nub, unfoldr, intercalate, isInfixOf )
import Data.Typeable
    ( cast )
import Data.Ord
    ( comparing )
import qualified Data.ByteString.Lazy as BS
import qualified Data.ByteString.Lazy.Char8 as BS.Char8
import qualified Data.Set as Set

import System.Directory
    ( Permissions(executable), getDirectoryContents, getPermissions
    , doesDirectoryExist, doesFileExist, removeFile, findExecutable
    , getModificationTime )
import System.Environment
    ( getProgName )
import System.Exit
    ( exitWith, ExitCode(..) )
import System.FilePath
    ( normalise, (</>), (<.>)
    , getSearchPath, joinPath, takeDirectory, splitFileName
    , splitExtension, splitExtensions, splitDirectories
    , searchPathSeparator )
import System.Directory
    ( createDirectory, renameFile, removeDirectoryRecursive )
import System.IO
    ( Handle, openFile, openBinaryFile, openBinaryTempFileWithDefaultPermissions
    , IOMode(ReadMode), hSetBinaryMode
    , hGetContents, stderr, stdout, hPutStr, hFlush, hClose )
import System.IO.Error as IO.Error
    ( isDoesNotExistError, isAlreadyExistsError
    , ioeSetFileName, ioeGetFileName, ioeGetErrorString )
import System.IO.Error
    ( ioeSetLocation, ioeGetLocation )
import System.IO.Unsafe
    ( unsafeInterleaveIO )
import qualified Control.Exception as Exception

import Control.Exception (IOException, evaluate, throwIO)
import Control.Concurrent (forkIO)
import qualified System.Process as Process
         ( CreateProcess(..), StdStream(..), proc)
import System.Process
         ( ProcessHandle, createProcess, rawSystem, runInteractiveProcess
         , showCommandForUser, waitForProcess)

-- We only get our own version number when we're building with ourselves
cabalVersion :: Version
#if defined(BOOTSTRAPPED_CABAL)
cabalVersion = Paths_Cabal.version
#elif defined(CABAL_VERSION)
cabalVersion = Version [CABAL_VERSION] []
#else
cabalVersion = Version [1,9999] []  --used when bootstrapping
#endif

-- ----------------------------------------------------------------------------
-- Exception and logging utils

dieWithLocation :: FilePath -> Maybe Int -> String -> IO a
dieWithLocation filename lineno msg =
  ioError . setLocation lineno
          . flip ioeSetFileName (normalise filename)
          $ userError msg
  where
    setLocation Nothing  err = err
    setLocation (Just n) err = ioeSetLocation err (show n)

die :: String -> IO a
die msg = ioError (userError msg)

topHandlerWith :: forall a. (Exception.SomeException -> IO a) -> IO a -> IO a
topHandlerWith cont prog =
    Exception.catches prog [
        Exception.Handler rethrowAsyncExceptions
      , Exception.Handler rethrowExitStatus
      , Exception.Handler handle
      ]
  where
    -- Let async exceptions rise to the top for the default top-handler
    rethrowAsyncExceptions :: Exception.AsyncException -> IO a
    rethrowAsyncExceptions = throwIO

    -- ExitCode gets thrown asynchronously too, and we don't want to print it
    rethrowExitStatus :: ExitCode -> IO a
    rethrowExitStatus = throwIO

    -- Print all other exceptions
    handle :: Exception.SomeException -> IO a
    handle se = do
      hFlush stdout
      pname <- getProgName
      hPutStr stderr (message pname se)
      cont se

    message :: String -> Exception.SomeException -> String
    message pname (Exception.SomeException se) =
      case cast se :: Maybe Exception.IOException of
        Just ioe ->
          let file         = case ioeGetFileName ioe of
                               Nothing   -> ""
                               Just path -> path ++ location ++ ": "
              location     = case ioeGetLocation ioe of
                               l@(n:_) | Char.isDigit n -> ':' : l
                               _                        -> ""
              detail       = ioeGetErrorString ioe
          in wrapText (pname ++ ": " ++ file ++ detail)
        Nothing ->
#if __GLASGOW_HASKELL__ < 710
          show se
#else
          Exception.displayException se
#endif

topHandler :: IO a -> IO a
topHandler prog = topHandlerWith (const $ exitWith (ExitFailure 1)) prog

-- | Non fatal conditions that may be indicative of an error or problem.
--
-- We display these at the 'normal' verbosity level.
--
warn :: Verbosity -> String -> IO ()
warn verbosity msg =
  when (verbosity >= normal) $ do
    hFlush stdout
    hPutStr stderr (wrapText ("Warning: " ++ msg))

-- | Useful status messages.
--
-- We display these at the 'normal' verbosity level.
--
-- This is for the ordinary helpful status messages that users see. Just
-- enough information to know that things are working but not floods of detail.
--
notice :: Verbosity -> String -> IO ()
notice verbosity msg =
  when (verbosity >= normal) $
    putStr (wrapText msg)

setupMessage :: Verbosity -> String -> PackageIdentifier -> IO ()
setupMessage verbosity msg pkgid =
    notice verbosity (msg ++ ' ': display pkgid ++ "...")

-- | More detail on the operation of some action.
--
-- We display these messages when the verbosity level is 'verbose'
--
info :: Verbosity -> String -> IO ()
info verbosity msg =
  when (verbosity >= verbose) $
    putStr (wrapText msg)

-- | Detailed internal debugging information
--
-- We display these messages when the verbosity level is 'deafening'
--
debug :: Verbosity -> String -> IO ()
debug verbosity msg =
  when (verbosity >= deafening) $ do
    putStr (wrapText msg)
    hFlush stdout

-- | A variant of 'debug' that doesn't perform the automatic line
-- wrapping. Produces better output in some cases.
debugNoWrap :: Verbosity -> String -> IO ()
debugNoWrap verbosity msg =
  when (verbosity >= deafening) $ do
    putStrLn msg
    hFlush stdout

-- | Perform an IO action, catching any IO exceptions and printing an error
--   if one occurs.
chattyTry :: String  -- ^ a description of the action we were attempting
          -> IO ()   -- ^ the action itself
          -> IO ()
chattyTry desc action =
  catchIO action $ \exception ->
    putStrLn $ "Error while " ++ desc ++ ": " ++ show exception

-- | Run an IO computation, returning @e@ if it raises a "file
-- does not exist" error.
handleDoesNotExist :: a -> IO a -> IO a
handleDoesNotExist e =
    Exception.handleJust
      (\ioe -> if isDoesNotExistError ioe then Just ioe else Nothing)
      (\_ -> return e)

-- -----------------------------------------------------------------------------
-- Helper functions

-- | Wraps text to the default line width. Existing newlines are preserved.
wrapText :: String -> String
wrapText = unlines
         . map (intercalate "\n"
              . map unwords
              . wrapLine 79
              . words)
         . lines

-- | Wraps a list of words to a list of lines of words of a particular width.
wrapLine :: Int -> [String] -> [[String]]
wrapLine width = wrap 0 []
  where wrap :: Int -> [String] -> [String] -> [[String]]
        wrap 0   []   (w:ws)
          | length w + 1 > width
          = wrap (length w) [w] ws
        wrap col line (w:ws)
          | col + length w + 1 > width
          = reverse line : wrap 0 [] (w:ws)
        wrap col line (w:ws)
          = let col' = col + length w + 1
             in wrap col' (w:line) ws
        wrap _ []   [] = []
        wrap _ line [] = [reverse line]

-- -----------------------------------------------------------------------------
-- rawSystem variants
maybeExit :: IO ExitCode -> IO ()
maybeExit cmd = do
  res <- cmd
  unless (res == ExitSuccess) $ exitWith res

printRawCommandAndArgs :: Verbosity -> FilePath -> [String] -> IO ()
printRawCommandAndArgs verbosity path args =
    printRawCommandAndArgsAndEnv verbosity path args Nothing

printRawCommandAndArgsAndEnv :: Verbosity
                             -> FilePath
                             -> [String]
                             -> Maybe [(String, String)]
                             -> IO ()
printRawCommandAndArgsAndEnv verbosity path args menv
 | verbosity >= deafening = do
       traverse_ (putStrLn . ("Environment: " ++) . show) menv
       print (path, args)
 | verbosity >= verbose   = putStrLn $ showCommandForUser path args
 | otherwise              = return ()


-- Exit with the same exit code if the subcommand fails
rawSystemExit :: Verbosity -> FilePath -> [String] -> IO ()
rawSystemExit verbosity path args = do
  printRawCommandAndArgs verbosity path args
  hFlush stdout
  exitcode <- rawSystem path args
  unless (exitcode == ExitSuccess) $ do
    debug verbosity $ path ++ " returned " ++ show exitcode
    exitWith exitcode

rawSystemExitCode :: Verbosity -> FilePath -> [String] -> IO ExitCode
rawSystemExitCode verbosity path args = do
  printRawCommandAndArgs verbosity path args
  hFlush stdout
  exitcode <- rawSystem path args
  unless (exitcode == ExitSuccess) $ do
    debug verbosity $ path ++ " returned " ++ show exitcode
  return exitcode

rawSystemExitWithEnv :: Verbosity
                     -> FilePath
                     -> [String]
                     -> [(String, String)]
                     -> IO ()
rawSystemExitWithEnv verbosity path args env = do
    printRawCommandAndArgsAndEnv verbosity path args (Just env)
    hFlush stdout
    (_,_,_,ph) <- createProcess $
                  (Process.proc path args) { Process.env = (Just env)
#ifdef MIN_VERSION_process
#if MIN_VERSION_process(1,2,0)
-- delegate_ctlc has been added in process 1.2, and we still want to be able to
-- bootstrap GHC on systems not having that version
                                           , Process.delegate_ctlc = True
#endif
#endif
                                           }
    exitcode <- waitForProcess ph
    unless (exitcode == ExitSuccess) $ do
        debug verbosity $ path ++ " returned " ++ show exitcode
        exitWith exitcode

-- Closes the passed in handles before returning.
rawSystemIOWithEnv :: Verbosity
                   -> FilePath
                   -> [String]
                   -> Maybe FilePath           -- ^ New working dir or inherit
                   -> Maybe [(String, String)] -- ^ New environment or inherit
                   -> Maybe Handle  -- ^ stdin
                   -> Maybe Handle  -- ^ stdout
                   -> Maybe Handle  -- ^ stderr
                   -> IO ExitCode
rawSystemIOWithEnv verbosity path args mcwd menv inp out err = do
    (_,_,_,ph) <- createProcessWithEnv verbosity path args mcwd menv
                                       (mbToStd inp) (mbToStd out) (mbToStd err)
    exitcode <- waitForProcess ph
    unless (exitcode == ExitSuccess) $ do
      debug verbosity $ path ++ " returned " ++ show exitcode
    return exitcode
  where
    mbToStd :: Maybe Handle -> Process.StdStream
    mbToStd = maybe Process.Inherit Process.UseHandle

createProcessWithEnv ::
  Verbosity
  -> FilePath
  -> [String]
  -> Maybe FilePath           -- ^ New working dir or inherit
  -> Maybe [(String, String)] -- ^ New environment or inherit
  -> Process.StdStream  -- ^ stdin
  -> Process.StdStream  -- ^ stdout
  -> Process.StdStream  -- ^ stderr
  -> IO (Maybe Handle, Maybe Handle, Maybe Handle,ProcessHandle)
  -- ^ Any handles created for stdin, stdout, or stderr
  -- with 'CreateProcess', and a handle to the process.
createProcessWithEnv verbosity path args mcwd menv inp out err = do
    printRawCommandAndArgsAndEnv verbosity path args menv
    hFlush stdout
    (inp', out', err', ph) <- createProcess $
                                (Process.proc path args) {
                                    Process.cwd           = mcwd
                                  , Process.env           = menv
                                  , Process.std_in        = inp
                                  , Process.std_out       = out
                                  , Process.std_err       = err
#ifdef MIN_VERSION_process
#if MIN_VERSION_process(1,2,0)
-- delegate_ctlc has been added in process 1.2, and we still want to be able to
-- bootstrap GHC on systems not having that version
                                  , Process.delegate_ctlc = True
#endif
#endif
                                  }
    return (inp', out', err', ph)

-- | Run a command and return its output.
--
-- The output is assumed to be text in the locale encoding.
--
rawSystemStdout :: Verbosity -> FilePath -> [String] -> IO String
rawSystemStdout verbosity path args = do
  (output, errors, exitCode) <- rawSystemStdInOut verbosity path args
                                                  Nothing Nothing
                                                  Nothing False
  when (exitCode /= ExitSuccess) $
    die errors
  return output

-- | Run a command and return its output, errors and exit status. Optionally
-- also supply some input. Also provides control over whether the binary/text
-- mode of the input and output.
--
rawSystemStdInOut :: Verbosity
                  -> FilePath                 -- ^ Program location
                  -> [String]                 -- ^ Arguments
                  -> Maybe FilePath           -- ^ New working dir or inherit
                  -> Maybe [(String, String)] -- ^ New environment or inherit
                  -> Maybe (String, Bool)     -- ^ input text and binary mode
                  -> Bool                     -- ^ output in binary mode
                  -> IO (String, String, ExitCode) -- ^ output, errors, exit
rawSystemStdInOut verbosity path args mcwd menv input outputBinary = do
  printRawCommandAndArgs verbosity path args

  Exception.bracket
     (runInteractiveProcess path args mcwd menv)
     (\(inh,outh,errh,_) -> hClose inh >> hClose outh >> hClose errh)
    $ \(inh,outh,errh,pid) -> do

      -- output mode depends on what the caller wants
      hSetBinaryMode outh outputBinary
      -- but the errors are always assumed to be text (in the current locale)
      hSetBinaryMode errh False

      -- fork off a couple threads to pull on the stderr and stdout
      -- so if the process writes to stderr we do not block.

      err <- hGetContents errh
      out <- hGetContents outh

      mv <- newEmptyMVar
      let force str = (evaluate (length str) >> return ())
            `Exception.finally` putMVar mv ()
          --TODO: handle exceptions like text decoding.
      _ <- forkIO $ force out
      _ <- forkIO $ force err

      -- push all the input, if any
      case input of
        Nothing -> return ()
        Just (inputStr, inputBinary) -> do
                -- input mode depends on what the caller wants
          hSetBinaryMode inh inputBinary
          hPutStr inh inputStr
          hClose inh
          --TODO: this probably fails if the process refuses to consume
          -- or if it closes stdin (eg if it exits)

      -- wait for both to finish, in either order
      takeMVar mv
      takeMVar mv

      -- wait for the program to terminate
      exitcode <- waitForProcess pid
      unless (exitcode == ExitSuccess) $
        debug verbosity $ path ++ " returned " ++ show exitcode
                       ++ if null err then "" else
                          " with error message:\n" ++ err
                       ++ case input of
                            Nothing       -> ""
                            Just ("",  _) -> ""
                            Just (inp, _) -> "\nstdin input:\n" ++ inp

      return (out, err, exitcode)


{-# DEPRECATED findProgramLocation
    "No longer used within Cabal, try findProgramOnSearchPath" #-}
-- | Look for a program on the path.
findProgramLocation :: Verbosity -> FilePath -> IO (Maybe FilePath)
findProgramLocation verbosity prog = do
  debug verbosity $ "searching for " ++ prog ++ " in path."
  res <- findExecutable prog
  case res of
      Nothing   -> debug verbosity ("Cannot find " ++ prog ++ " on the path")
      Just path -> debug verbosity ("found " ++ prog ++ " at "++ path)
  return res


-- | Look for a program and try to find it's version number. It can accept
-- either an absolute path or the name of a program binary, in which case we
-- will look for the program on the path.
--
findProgramVersion :: String             -- ^ version args
                   -> (String -> String) -- ^ function to select version
                                         --   number from program output
                   -> Verbosity
                   -> FilePath           -- ^ location
                   -> IO (Maybe Version)
findProgramVersion versionArg selectVersion verbosity path = do
  str <- rawSystemStdout verbosity path [versionArg]
         `catchIO`   (\_ -> return "")
         `catchExit` (\_ -> return "")
  let version :: Maybe Version
      version = simpleParse (selectVersion str)
  case version of
      Nothing -> warn verbosity $ "cannot determine version of " ++ path
                               ++ " :\n" ++ show str
      Just v  -> debug verbosity $ path ++ " is version " ++ display v
  return version


-- | Like the Unix xargs program. Useful for when we've got very long command
-- lines that might overflow an OS limit on command line length and so you
-- need to invoke a command multiple times to get all the args in.
--
-- Use it with either of the rawSystem variants above. For example:
--
-- > xargs (32*1024) (rawSystemExit verbosity) prog fixedArgs bigArgs
--
xargs :: Int -> ([String] -> IO ())
      -> [String] -> [String] -> IO ()
xargs maxSize rawSystemFun fixedArgs bigArgs =
  let fixedArgSize = sum (map length fixedArgs) + length fixedArgs
      chunkSize = maxSize - fixedArgSize
   in mapM_ (rawSystemFun . (fixedArgs ++)) (chunks chunkSize bigArgs)

  where chunks len = unfoldr $ \s ->
          if null s then Nothing
                    else Just (chunk [] len s)

        chunk acc _   []     = (reverse acc,[])
        chunk acc len (s:ss)
          | len' < len = chunk (s:acc) (len-len'-1) ss
          | otherwise  = (reverse acc, s:ss)
          where len' = length s

-- ------------------------------------------------------------
-- * File Utilities
-- ------------------------------------------------------------

----------------
-- Finding files

-- | Find a file by looking in a search path. The file path must match exactly.
--
findFile :: [FilePath]    -- ^search locations
         -> FilePath      -- ^File Name
         -> IO FilePath
findFile searchPath fileName =
  findFirstFile id
    [ path </> fileName
    | path <- nub searchPath]
  >>= maybe (die $ fileName ++ " doesn't exist") return

-- | Find a file by looking in a search path with one of a list of possible
-- file extensions. The file base name should be given and it will be tried
-- with each of the extensions in each element of the search path.
--
findFileWithExtension :: [String]
                      -> [FilePath]
                      -> FilePath
                      -> IO (Maybe FilePath)
findFileWithExtension extensions searchPath baseName =
  findFirstFile id
    [ path </> baseName <.> ext
    | path <- nub searchPath
    , ext <- nub extensions ]

findAllFilesWithExtension :: [String]
                          -> [FilePath]
                          -> FilePath
                          -> IO [FilePath]
findAllFilesWithExtension extensions searchPath basename =
  findAllFiles id
    [ path </> basename <.> ext
    | path <- nub searchPath
    , ext <- nub extensions ]

-- | Like 'findFileWithExtension' but returns which element of the search path
-- the file was found in, and the file path relative to that base directory.
--
findFileWithExtension' :: [String]
                       -> [FilePath]
                       -> FilePath
                       -> IO (Maybe (FilePath, FilePath))
findFileWithExtension' extensions searchPath baseName =
  findFirstFile (uncurry (</>))
    [ (path, baseName <.> ext)
    | path <- nub searchPath
    , ext <- nub extensions ]

findFirstFile :: (a -> FilePath) -> [a] -> IO (Maybe a)
findFirstFile file = findFirst
  where findFirst []     = return Nothing
        findFirst (x:xs) = do exists <- doesFileExist (file x)
                              if exists
                                then return (Just x)
                                else findFirst xs

findAllFiles :: (a -> FilePath) -> [a] -> IO [a]
findAllFiles file = filterM (doesFileExist . file)

-- | Finds the files corresponding to a list of Haskell module names.
--
-- As 'findModuleFile' but for a list of module names.
--
findModuleFiles :: [FilePath]   -- ^ build prefix (location of objects)
                -> [String]     -- ^ search suffixes
                -> [ModuleName] -- ^ modules
                -> IO [(FilePath, FilePath)]
findModuleFiles searchPath extensions moduleNames =
  mapM (findModuleFile searchPath extensions) moduleNames

-- | Find the file corresponding to a Haskell module name.
--
-- This is similar to 'findFileWithExtension'' but specialised to a module
-- name. The function fails if the file corresponding to the module is missing.
--
findModuleFile :: [FilePath]  -- ^ build prefix (location of objects)
               -> [String]    -- ^ search suffixes
               -> ModuleName  -- ^ module
               -> IO (FilePath, FilePath)
findModuleFile searchPath extensions moduleName =
      maybe notFound return
  =<< findFileWithExtension' extensions searchPath
                             (ModuleName.toFilePath moduleName)
  where
    notFound = die $ "Error: Could not find module: " ++ display moduleName
                  ++ " with any suffix: " ++ show extensions
                  ++ " in the search path: " ++ show searchPath

-- | List all the files in a directory and all subdirectories.
--
-- The order places files in sub-directories after all the files in their
-- parent directories. The list is generated lazily so is not well defined if
-- the source directory structure changes before the list is used.
--
getDirectoryContentsRecursive :: FilePath -> IO [FilePath]
getDirectoryContentsRecursive topdir = recurseDirectories [""]
  where
    recurseDirectories :: [FilePath] -> IO [FilePath]
    recurseDirectories []         = return []
    recurseDirectories (dir:dirs) = unsafeInterleaveIO $ do
      (files, dirs') <- collect [] [] =<< getDirectoryContents (topdir </> dir)
      files' <- recurseDirectories (dirs' ++ dirs)
      return (files ++ files')

      where
        collect files dirs' []              = return (reverse files
                                                     ,reverse dirs')
        collect files dirs' (entry:entries) | ignore entry
                                            = collect files dirs' entries
        collect files dirs' (entry:entries) = do
          let dirEntry = dir </> entry
          isDirectory <- doesDirectoryExist (topdir </> dirEntry)
          if isDirectory
            then collect files (dirEntry:dirs') entries
            else collect (dirEntry:files) dirs' entries

        ignore ['.']      = True
        ignore ['.', '.'] = True
        ignore _          = False

------------------------
-- Environment variables

-- | Is this directory in the system search path?
isInSearchPath :: FilePath -> IO Bool
isInSearchPath path = fmap (elem path) getSearchPath

addLibraryPath :: OS
               -> [FilePath]
               -> [(String,String)]
               -> [(String,String)]
addLibraryPath os paths = addEnv
  where
    pathsString = intercalate [searchPathSeparator] paths
    ldPath = case os of
               OSX -> "DYLD_LIBRARY_PATH"
               _   -> "LD_LIBRARY_PATH"

    addEnv [] = [(ldPath,pathsString)]
    addEnv ((key,value):xs)
      | key == ldPath =
          if null value
             then (key,pathsString):xs
             else (key,value ++ (searchPathSeparator:pathsString)):xs
      | otherwise     = (key,value):addEnv xs

----------------
-- File globbing

data FileGlob
   -- | No glob at all, just an ordinary file
   = NoGlob FilePath

   -- | dir prefix and extension, like @\"foo\/bar\/\*.baz\"@ corresponds to
   --    @FileGlob \"foo\/bar\" \".baz\"@
   | FileGlob FilePath String

parseFileGlob :: FilePath -> Maybe FileGlob
parseFileGlob filepath = case splitExtensions filepath of
  (filepath', ext) -> case splitFileName filepath' of
    (dir, "*") | '*' `elem` dir
              || '*' `elem` ext
              || null ext            -> Nothing
               | null dir            -> Just (FileGlob "." ext)
               | otherwise           -> Just (FileGlob dir ext)
    _          | '*' `elem` filepath -> Nothing
               | otherwise           -> Just (NoGlob filepath)

matchFileGlob :: FilePath -> IO [FilePath]
matchFileGlob = matchDirFileGlob "."

matchDirFileGlob :: FilePath -> FilePath -> IO [FilePath]
matchDirFileGlob dir filepath = case parseFileGlob filepath of
  Nothing -> die $ "invalid file glob '" ++ filepath
                ++ "'. Wildcards '*' are only allowed in place of the file"
                ++ " name, not in the directory name or file extension."
                ++ " If a wildcard is used it must be with an file extension."
  Just (NoGlob filepath') -> return [filepath']
  Just (FileGlob dir' ext) -> do
    files <- getDirectoryContents (dir </> dir')
    case   [ dir' </> file
           | file <- files
           , let (name, ext') = splitExtensions file
           , not (null name) && ext' == ext ] of
      []      -> die $ "filepath wildcard '" ++ filepath
                    ++ "' does not match any files."
      matches -> return matches

--------------------
-- Modification time

-- | Compare the modification times of two files to see if the first is newer
-- than the second. The first file must exist but the second need not.
-- The expected use case is when the second file is generated using the first.
-- In this use case, if the result is True then the second file is out of date.
--
moreRecentFile :: FilePath -> FilePath -> IO Bool
moreRecentFile a b = do
  exists <- doesFileExist b
  if not exists
    then return True
    else do tb <- getModificationTime b
            ta <- getModificationTime a
            return (ta > tb)

-- | Like 'moreRecentFile', but also checks that the first file exists.
existsAndIsMoreRecentThan :: FilePath -> FilePath -> IO Bool
existsAndIsMoreRecentThan a b = do
  exists <- doesFileExist a
  if not exists
    then return False
    else a `moreRecentFile` b

----------------------------------------
-- Copying and installing files and dirs

-- | Same as 'createDirectoryIfMissing' but logs at higher verbosity levels.
--
createDirectoryIfMissingVerbose :: Verbosity
                                -> Bool     -- ^ Create its parents too?
                                -> FilePath
                                -> IO ()
createDirectoryIfMissingVerbose verbosity create_parents path0
  | create_parents = createDirs (parents path0)
  | otherwise      = createDirs (take 1 (parents path0))
  where
    parents = reverse . scanl1 (</>) . splitDirectories . normalise

    createDirs []         = return ()
    createDirs (dir:[])   = createDir dir throwIO
    createDirs (dir:dirs) =
      createDir dir $ \_ -> do
        createDirs dirs
        createDir dir throwIO

    createDir :: FilePath -> (IOException -> IO ()) -> IO ()
    createDir dir notExistHandler = do
      r <- tryIO $ createDirectoryVerbose verbosity dir
      case (r :: Either IOException ()) of
        Right ()                   -> return ()
        Left  e
          | isDoesNotExistError  e -> notExistHandler e
          -- createDirectory (and indeed POSIX mkdir) does not distinguish
          -- between a dir already existing and a file already existing. So we
          -- check for it here. Unfortunately there is a slight race condition
          -- here, but we think it is benign. It could report an exception in
          -- the case that the dir did exist but another process deletes the
          -- directory and creates a file in its place before we can check
          -- that the directory did indeed exist.
          | isAlreadyExistsError e -> (do
              isDir <- doesDirectoryExist dir
              if isDir then return ()
                       else throwIO e
              ) `catchIO` ((\_ -> return ()) :: IOException -> IO ())
          | otherwise              -> throwIO e

createDirectoryVerbose :: Verbosity -> FilePath -> IO ()
createDirectoryVerbose verbosity dir = do
  info verbosity $ "creating " ++ dir
  createDirectory dir
  setDirOrdinary dir

-- | Copies a file without copying file permissions. The target file is created
-- with default permissions. Any existing target file is replaced.
--
-- At higher verbosity levels it logs an info message.
--
copyFileVerbose :: Verbosity -> FilePath -> FilePath -> IO ()
copyFileVerbose verbosity src dest = do
  info verbosity ("copy " ++ src ++ " to " ++ dest)
  copyFile src dest

-- | Install an ordinary file. This is like a file copy but the permissions
-- are set appropriately for an installed file. On Unix it is \"-rw-r--r--\"
-- while on Windows it uses the default permissions for the target directory.
--
installOrdinaryFile :: Verbosity -> FilePath -> FilePath -> IO ()
installOrdinaryFile verbosity src dest = do
  info verbosity ("Installing " ++ src ++ " to " ++ dest)
  copyOrdinaryFile src dest

-- | Install an executable file. This is like a file copy but the permissions
-- are set appropriately for an installed file. On Unix it is \"-rwxr-xr-x\"
-- while on Windows it uses the default permissions for the target directory.
--
installExecutableFile :: Verbosity -> FilePath -> FilePath -> IO ()
installExecutableFile verbosity src dest = do
  info verbosity ("Installing executable " ++ src ++ " to " ++ dest)
  copyExecutableFile src dest

-- | Install a file that may or not be executable, preserving permissions.
installMaybeExecutableFile :: Verbosity -> FilePath -> FilePath -> IO ()
installMaybeExecutableFile verbosity src dest = do
  perms <- getPermissions src
  if (executable perms) --only checks user x bit
    then installExecutableFile verbosity src dest
    else installOrdinaryFile   verbosity src dest

-- | Given a relative path to a file, copy it to the given directory, preserving
-- the relative path and creating the parent directories if needed.
copyFileTo :: Verbosity -> FilePath -> FilePath -> IO ()
copyFileTo verbosity dir file = do
  let targetFile = dir </> file
  createDirectoryIfMissingVerbose verbosity True (takeDirectory targetFile)
  installOrdinaryFile verbosity file targetFile

-- | Common implementation of 'copyFiles', 'installOrdinaryFiles',
-- 'installExecutableFiles' and 'installMaybeExecutableFiles'.
copyFilesWith :: (Verbosity -> FilePath -> FilePath -> IO ())
              -> Verbosity -> FilePath -> [(FilePath, FilePath)] -> IO ()
copyFilesWith doCopy verbosity targetDir srcFiles = do

  -- Create parent directories for everything
  let dirs = map (targetDir </>) . nub . map (takeDirectory . snd) $ srcFiles
  mapM_ (createDirectoryIfMissingVerbose verbosity True) dirs

  -- Copy all the files
  sequence_ [ let src  = srcBase   </> srcFile
                  dest = targetDir </> srcFile
               in doCopy verbosity src dest
            | (srcBase, srcFile) <- srcFiles ]

-- | Copies a bunch of files to a target directory, preserving the directory
-- structure in the target location. The target directories are created if they
-- do not exist.
--
-- The files are identified by a pair of base directory and a path relative to
-- that base. It is only the relative part that is preserved in the
-- destination.
--
-- For example:
--
-- > copyFiles normal "dist/src"
-- >    [("", "src/Foo.hs"), ("dist/build/", "src/Bar.hs")]
--
-- This would copy \"src\/Foo.hs\" to \"dist\/src\/src\/Foo.hs\" and
-- copy \"dist\/build\/src\/Bar.hs\" to \"dist\/src\/src\/Bar.hs\".
--
-- This operation is not atomic. Any IO failure during the copy (including any
-- missing source files) leaves the target in an unknown state so it is best to
-- use it with a freshly created directory so that it can be simply deleted if
-- anything goes wrong.
--
copyFiles :: Verbosity -> FilePath -> [(FilePath, FilePath)] -> IO ()
copyFiles = copyFilesWith copyFileVerbose

-- | This is like 'copyFiles' but uses 'installOrdinaryFile'.
--
installOrdinaryFiles :: Verbosity -> FilePath -> [(FilePath, FilePath)] -> IO ()
installOrdinaryFiles = copyFilesWith installOrdinaryFile

-- | This is like 'copyFiles' but uses 'installExecutableFile'.
--
installExecutableFiles :: Verbosity -> FilePath -> [(FilePath, FilePath)]
                          -> IO ()
installExecutableFiles = copyFilesWith installExecutableFile

-- | This is like 'copyFiles' but uses 'installMaybeExecutableFile'.
--
installMaybeExecutableFiles :: Verbosity -> FilePath -> [(FilePath, FilePath)]
                               -> IO ()
installMaybeExecutableFiles = copyFilesWith installMaybeExecutableFile

-- | This installs all the files in a directory to a target location,
-- preserving the directory layout. All the files are assumed to be ordinary
-- rather than executable files.
--
installDirectoryContents :: Verbosity -> FilePath -> FilePath -> IO ()
installDirectoryContents verbosity srcDir destDir = do
  info verbosity ("copy directory '" ++ srcDir ++ "' to '" ++ destDir ++ "'.")
  srcFiles <- getDirectoryContentsRecursive srcDir
  installOrdinaryFiles verbosity destDir [ (srcDir, f) | f <- srcFiles ]

-- | Recursively copy the contents of one directory to another path.
copyDirectoryRecursive :: Verbosity -> FilePath -> FilePath -> IO ()
copyDirectoryRecursive verbosity srcDir destDir = do
  info verbosity ("copy directory '" ++ srcDir ++ "' to '" ++ destDir ++ "'.")
  srcFiles <- getDirectoryContentsRecursive srcDir
  copyFilesWith (const copyFile) verbosity destDir [ (srcDir, f)
                                                   | f <- srcFiles ]

-------------------
-- File permissions

-- | Like 'doesFileExist', but also checks that the file is executable.
doesExecutableExist :: FilePath -> IO Bool
doesExecutableExist f = do
  exists <- doesFileExist f
  if exists
    then do perms <- getPermissions f
            return (executable perms)
    else return False

---------------------------------
-- Deprecated file copy functions

{-# DEPRECATED smartCopySources
      "Use findModuleFiles and copyFiles or installOrdinaryFiles" #-}
smartCopySources :: Verbosity -> [FilePath] -> FilePath
                 -> [ModuleName] -> [String] -> IO ()
smartCopySources verbosity searchPath targetDir moduleNames extensions =
      findModuleFiles searchPath extensions moduleNames
  >>= copyFiles verbosity targetDir

{-# DEPRECATED copyDirectoryRecursiveVerbose
      "You probably want installDirectoryContents instead" #-}
copyDirectoryRecursiveVerbose :: Verbosity -> FilePath -> FilePath -> IO ()
copyDirectoryRecursiveVerbose verbosity srcDir destDir = do
  info verbosity ("copy directory '" ++ srcDir ++ "' to '" ++ destDir ++ "'.")
  srcFiles <- getDirectoryContentsRecursive srcDir
  copyFiles verbosity destDir [ (srcDir, f) | f <- srcFiles ]

---------------------------
-- Temporary files and dirs

-- | Advanced options for 'withTempFile' and 'withTempDirectory'.
data TempFileOptions = TempFileOptions {
  optKeepTempFiles :: Bool  -- ^ Keep temporary files?
  }

defaultTempFileOptions :: TempFileOptions
defaultTempFileOptions = TempFileOptions { optKeepTempFiles = False }

-- | Use a temporary filename that doesn't already exist.
--
withTempFile :: FilePath    -- ^ Temp dir to create the file in
                -> String   -- ^ File name template. See 'openTempFile'.
                -> (FilePath -> Handle -> IO a) -> IO a
withTempFile tmpDir template action =
  withTempFileEx defaultTempFileOptions tmpDir template action

-- | A version of 'withTempFile' that additionally takes a 'TempFileOptions'
-- argument.
withTempFileEx :: TempFileOptions
                 -> FilePath -- ^ Temp dir to create the file in
                 -> String   -- ^ File name template. See 'openTempFile'.
                 -> (FilePath -> Handle -> IO a) -> IO a
withTempFileEx opts tmpDir template action =
  Exception.bracket
    (openTempFile tmpDir template)
    (\(name, handle) -> do hClose handle
                           unless (optKeepTempFiles opts) $
                             handleDoesNotExist () . removeFile $ name)
    (uncurry action)

-- | Create and use a temporary directory.
--
-- Creates a new temporary directory inside the given directory, making use
-- of the template. The temp directory is deleted after use. For example:
--
-- > withTempDirectory verbosity "src" "sdist." $ \tmpDir -> do ...
--
-- The @tmpDir@ will be a new subdirectory of the given directory, e.g.
-- @src/sdist.342@.
--
withTempDirectory :: Verbosity
                     -> FilePath -> String -> (FilePath -> IO a) -> IO a
withTempDirectory verbosity targetDir template =
  withTempDirectoryEx verbosity defaultTempFileOptions targetDir template

-- | A version of 'withTempDirectory' that additionally takes a
-- 'TempFileOptions' argument.
withTempDirectoryEx :: Verbosity
                       -> TempFileOptions
                       -> FilePath -> String -> (FilePath -> IO a) -> IO a
withTempDirectoryEx _verbosity opts targetDir template =
  Exception.bracket
    (createTempDirectory targetDir template)
    (unless (optKeepTempFiles opts)
     . handleDoesNotExist () . removeDirectoryRecursive)

-----------------------------------
-- Safely reading and writing files

-- | Gets the contents of a file, but guarantee that it gets closed.
--
-- The file is read lazily but if it is not fully consumed by the action then
-- the remaining input is truncated and the file is closed.
--
withFileContents :: FilePath -> (String -> IO a) -> IO a
withFileContents name action =
  Exception.bracket (openFile name ReadMode) hClose
                    (\hnd -> hGetContents hnd >>= action)

-- | Writes a file atomically.
--
-- The file is either written successfully or an IO exception is raised and
-- the original file is left unchanged.
--
-- On windows it is not possible to delete a file that is open by a process.
-- This case will give an IO exception but the atomic property is not affected.
--
writeFileAtomic :: FilePath -> BS.ByteString -> IO ()
writeFileAtomic targetPath content = do
  let (targetDir, targetFile) = splitFileName targetPath
  Exception.bracketOnError
    (openBinaryTempFileWithDefaultPermissions targetDir $ targetFile <.> "tmp")
    (\(tmpPath, handle) -> hClose handle >> removeFile tmpPath)
    (\(tmpPath, handle) -> do
        BS.hPut handle content
        hClose handle
        renameFile tmpPath targetPath)

-- | Write a file but only if it would have new content. If we would be writing
-- the same as the existing content then leave the file as is so that we do not
-- update the file's modification time.
--
-- NB: the file is assumed to be ASCII-encoded.
rewriteFile :: FilePath -> String -> IO ()
rewriteFile path newContent =
  flip catchIO mightNotExist $ do
    existingContent <- readFile path
    _ <- evaluate (length existingContent)
    unless (existingContent == newContent) $
      writeFileAtomic path (BS.Char8.pack newContent)
  where
    mightNotExist e | isDoesNotExistError e = writeFileAtomic path
                                              (BS.Char8.pack newContent)
                    | otherwise             = ioError e

-- | The path name that represents the current directory.
-- In Unix, it's @\".\"@, but this is system-specific.
-- (E.g. AmigaOS uses the empty string @\"\"@ for the current directory.)
currentDir :: FilePath
currentDir = "."

shortRelativePath :: FilePath -> FilePath -> FilePath
shortRelativePath from to =
    case dropCommonPrefix (splitDirectories from) (splitDirectories to) of
        (stuff, path) -> joinPath (map (const "..") stuff ++ path)
  where
    dropCommonPrefix :: Eq a => [a] -> [a] -> ([a],[a])
    dropCommonPrefix (x:xs) (y:ys)
        | x == y    = dropCommonPrefix xs ys
    dropCommonPrefix xs ys = (xs,ys)

-- | Drop the extension if it's one of 'exeExtensions', or return the path
-- unchanged.
dropExeExtension :: FilePath -> FilePath
dropExeExtension filepath =
  case splitExtension filepath of
    (filepath', extension) | extension `elem` exeExtensions -> filepath'
                           | otherwise                      -> filepath

-- | List of possible executable file extensions on the current platform.
exeExtensions :: [String]
exeExtensions = case buildOS of
  -- Possible improvement: on Windows, read the list of extensions from the
  -- PATHEXT environment variable. By default PATHEXT is ".com; .exe; .bat;
  -- .cmd".
  Windows -> ["", "exe"]
  Ghcjs   -> ["", "exe"]
  _       -> [""]

-- ------------------------------------------------------------
-- * Finding the description file
-- ------------------------------------------------------------

-- |Package description file (/pkgname/@.cabal@)
defaultPackageDesc :: Verbosity -> IO FilePath
defaultPackageDesc _verbosity = tryFindPackageDesc currentDir

-- |Find a package description file in the given directory.  Looks for
-- @.cabal@ files.
findPackageDesc :: FilePath                    -- ^Where to look
                -> IO (Either String FilePath) -- ^<pkgname>.cabal
findPackageDesc dir
 = do files <- getDirectoryContents dir
      -- to make sure we do not mistake a ~/.cabal/ dir for a <pkgname>.cabal
      -- file we filter to exclude dirs and null base file names:
      cabalFiles <- filterM doesFileExist
                       [ dir </> file
                       | file <- files
                       , let (name, ext) = splitExtension file
                       , not (null name) && ext == ".cabal" ]
      case cabalFiles of
        []          -> return (Left  noDesc)
        [cabalFile] -> return (Right cabalFile)
        multiple    -> return (Left  $ multiDesc multiple)

  where
    noDesc :: String
    noDesc = "No cabal file found.\n"
             ++ "Please create a package description file <pkgname>.cabal"

    multiDesc :: [String] -> String
    multiDesc l = "Multiple cabal files found.\n"
                  ++ "Please use only one of: "
                  ++ intercalate ", " l

-- |Like 'findPackageDesc', but calls 'die' in case of error.
tryFindPackageDesc :: FilePath -> IO FilePath
tryFindPackageDesc dir = either die return =<< findPackageDesc dir

-- |Optional auxiliary package information file (/pkgname/@.buildinfo@)
defaultHookedPackageDesc :: IO (Maybe FilePath)
defaultHookedPackageDesc = findHookedPackageDesc currentDir

-- |Find auxiliary package information in the given directory.
-- Looks for @.buildinfo@ files.
findHookedPackageDesc
    :: FilePath                 -- ^Directory to search
    -> IO (Maybe FilePath)      -- ^/dir/@\/@/pkgname/@.buildinfo@, if present
findHookedPackageDesc dir = do
    files <- getDirectoryContents dir
    buildInfoFiles <- filterM doesFileExist
                        [ dir </> file
                        | file <- files
                        , let (name, ext) = splitExtension file
                        , not (null name) && ext == buildInfoExt ]
    case buildInfoFiles of
        [] -> return Nothing
        [f] -> return (Just f)
        _ -> die ("Multiple files with extension " ++ buildInfoExt)

buildInfoExt  :: String
buildInfoExt = ".buildinfo"

-- ------------------------------------------------------------
-- * Unicode stuff
-- ------------------------------------------------------------

-- This is a modification of the UTF8 code from gtk2hs and the
-- utf8-string package.

fromUTF8 :: String -> String
fromUTF8 []     = []
fromUTF8 (c:cs)
  | c <= '\x7F' = c : fromUTF8 cs
  | c <= '\xBF' = replacementChar : fromUTF8 cs
  | c <= '\xDF' = twoBytes c cs
  | c <= '\xEF' = moreBytes 3 0x800     cs (ord c .&. 0xF)
  | c <= '\xF7' = moreBytes 4 0x10000   cs (ord c .&. 0x7)
  | c <= '\xFB' = moreBytes 5 0x200000  cs (ord c .&. 0x3)
  | c <= '\xFD' = moreBytes 6 0x4000000 cs (ord c .&. 0x1)
  | otherwise   = replacementChar : fromUTF8 cs
  where
    twoBytes c0 (c1:cs')
      | ord c1 .&. 0xC0 == 0x80
      = let d = ((ord c0 .&. 0x1F) `shiftL` 6)
             .|. (ord c1 .&. 0x3F)
         in if d >= 0x80
               then  chr d           : fromUTF8 cs'
               else  replacementChar : fromUTF8 cs'
    twoBytes _ cs' = replacementChar : fromUTF8 cs'

    moreBytes :: Int -> Int -> [Char] -> Int -> [Char]
    moreBytes 1 overlong cs' acc
      | overlong <= acc && acc <= 0x10FFFF
     && (acc < 0xD800 || 0xDFFF < acc)
     && (acc < 0xFFFE || 0xFFFF < acc)
      = chr acc : fromUTF8 cs'

      | otherwise
      = replacementChar : fromUTF8 cs'

    moreBytes byteCount overlong (cn:cs') acc
      | ord cn .&. 0xC0 == 0x80
      = moreBytes (byteCount-1) overlong cs'
          ((acc `shiftL` 6) .|. ord cn .&. 0x3F)

    moreBytes _ _ cs' _
      = replacementChar : fromUTF8 cs'

    replacementChar = '\xfffd'

toUTF8 :: String -> String
toUTF8 []        = []
toUTF8 (c:cs)
  | c <= '\x07F' = c
                 : toUTF8 cs
  | c <= '\x7FF' = chr (0xC0 .|. (w `shiftR` 6))
                 : chr (0x80 .|. (w .&. 0x3F))
                 : toUTF8 cs
  | c <= '\xFFFF'= chr (0xE0 .|.  (w `shiftR` 12))
                 : chr (0x80 .|. ((w `shiftR` 6)  .&. 0x3F))
                 : chr (0x80 .|.  (w .&. 0x3F))
                 : toUTF8 cs
  | otherwise    = chr (0xf0 .|.  (w `shiftR` 18))
                 : chr (0x80 .|. ((w `shiftR` 12)  .&. 0x3F))
                 : chr (0x80 .|. ((w `shiftR` 6)  .&. 0x3F))
                 : chr (0x80 .|.  (w .&. 0x3F))
                 : toUTF8 cs
  where w = ord c

-- | Whether BOM is at the beginning of the input
startsWithBOM :: String -> Bool
startsWithBOM ('\xFEFF':_) = True
startsWithBOM _            = False

-- | Check whether a file has Unicode byte order mark (BOM).
fileHasBOM :: FilePath -> IO Bool
fileHasBOM f = fmap (startsWithBOM . fromUTF8)
             . hGetContents =<< openBinaryFile f ReadMode

-- | Ignore a Unicode byte order mark (BOM) at the beginning of the input
--
ignoreBOM :: String -> String
ignoreBOM ('\xFEFF':string) = string
ignoreBOM string            = string

-- | Reads a UTF8 encoded text file as a Unicode String
--
-- Reads lazily using ordinary 'readFile'.
--
readUTF8File :: FilePath -> IO String
readUTF8File f = fmap (ignoreBOM . fromUTF8)
               . hGetContents =<< openBinaryFile f ReadMode

-- | Reads a UTF8 encoded text file as a Unicode String
--
-- Same behaviour as 'withFileContents'.
--
withUTF8FileContents :: FilePath -> (String -> IO a) -> IO a
withUTF8FileContents name action =
  Exception.bracket
    (openBinaryFile name ReadMode)
    hClose
    (\hnd -> hGetContents hnd >>= action . ignoreBOM . fromUTF8)

-- | Writes a Unicode String as a UTF8 encoded text file.
--
-- Uses 'writeFileAtomic', so provides the same guarantees.
--
writeUTF8File :: FilePath -> String -> IO ()
writeUTF8File path = writeFileAtomic path . BS.Char8.pack . toUTF8

-- | Fix different systems silly line ending conventions
normaliseLineEndings :: String -> String
normaliseLineEndings [] = []
normaliseLineEndings ('\r':'\n':s) = '\n' : normaliseLineEndings s -- windows
normaliseLineEndings ('\r':s)      = '\n' : normaliseLineEndings s -- old OS X
normaliseLineEndings (  c :s)      =   c  : normaliseLineEndings s

-- ------------------------------------------------------------
-- * Common utils
-- ------------------------------------------------------------

-- | @dropWhileEndLE p@ is equivalent to @reverse . dropWhile p . reverse@, but
-- quite a bit faster. The difference between "Data.List.dropWhileEnd" and this
-- version is that the one in "Data.List" is strict in elements, but spine-lazy,
-- while this one is spine-strict but lazy in elements. That's what @LE@ stands
-- for - "lazy in elements".
--
-- Example:
--
-- @
-- > tail $ Data.List.dropWhileEnd (<3) [undefined, 5, 4, 3, 2, 1]
-- *** Exception: Prelude.undefined
-- > tail $ dropWhileEndLE (<3) [undefined, 5, 4, 3, 2, 1]
-- [5,4,3]
-- > take 3 $ Data.List.dropWhileEnd (<3) [5, 4, 3, 2, 1, undefined]
-- [5,4,3]
-- > take 3 $ dropWhileEndLE (<3) [5, 4, 3, 2, 1, undefined]
-- *** Exception: Prelude.undefined
-- @
dropWhileEndLE :: (a -> Bool) -> [a] -> [a]
dropWhileEndLE p = foldr (\x r -> if null r && p x then [] else x:r) []

-- | @takeWhileEndLE p@ is equivalent to @reverse . takeWhile p . reverse@, but
-- is usually faster (as well as being easier to read).
takeWhileEndLE :: (a -> Bool) -> [a] -> [a]
takeWhileEndLE p = fst . foldr go ([], False)
  where
    go x (rest, done)
      | not done && p x = (x:rest, False)
      | otherwise = (rest, True)

-- | Like "Data.List.nub", but has @O(n log n)@ complexity instead of
-- @O(n^2)@. Code for 'ordNub' and 'listUnion' taken from Niklas Hambüchen's
-- <http://github.com/nh2/haskell-ordnub ordnub> package.
ordNub :: (Ord a) => [a] -> [a]
ordNub l = go Set.empty l
  where
    go _ [] = []
    go s (x:xs) = if x `Set.member` s then go s xs
                                      else x : go (Set.insert x s) xs

-- | Like "Data.List.union", but has @O(n log n)@ complexity instead of
-- @O(n^2)@.
listUnion :: (Ord a) => [a] -> [a] -> [a]
listUnion a b = a ++ ordNub (filter (`Set.notMember` aSet) b)
  where
    aSet = Set.fromList a

-- | A right-biased version of 'ordNub'.
--
-- Example:
--
-- @
-- > ordNub [1,2,1]
-- [1,2]
-- > ordNubRight [1,2,1]
-- [2,1]
-- @
ordNubRight :: (Ord a) => [a] -> [a]
ordNubRight = fst . foldr go ([], Set.empty)
  where
    go x p@(l, s) = if x `Set.member` s then p
                                        else (x:l, Set.insert x s)

-- | A right-biased version of 'listUnion'.
--
-- Example:
--
-- @
-- > listUnion [1,2,3,4,3] [2,1,1]
-- [1,2,3,4,3]
-- > listUnionRight [1,2,3,4,3] [2,1,1]
-- [4,3,2,1,1]
-- @
listUnionRight :: (Ord a) => [a] -> [a] -> [a]
listUnionRight a b = ordNubRight (filter (`Set.notMember` bSet) a) ++ b
  where
    bSet = Set.fromList b

-- | A total variant of 'tail'.
safeTail :: [a] -> [a]
safeTail []     = []
safeTail (_:xs) = xs

equating :: Eq a => (b -> a) -> b -> b -> Bool
equating p x y = p x == p y

lowercase :: String -> String
lowercase = map Char.toLower
