    {- Temporary files.
     -
     - Copyright 2010-2013 Joey Hess <id@joeyh.name>
     -
     - License: BSD-2-clause
     -}

    {-# LANGUAGE CPP #-}
    {-# OPTIONS_GHC -fno-warn-tabs #-}

    module Utility.Tmp where

    import System.IO
    import System.FilePath
    import System.Directory
    import Control.Monad.IO.Class
    import System.PosixCompat.Files

    import Utility.Exception
    import Utility.FileSystemEncoding

    type Template = String

    {- Runs an action like writeFile, writing to a temp file first and
     - then moving it into place. The temp file is stored in the same
     - directory as the final file to avoid cross-device renames. -}
    viaTmp :: (MonadMask m, MonadIO m) => (FilePath -> v -> m ()) -> FilePath -> v -> m ()
    viaTmp a file content = bracketIO setup cleanup use
      where
            (dir, base) = splitFileName file
            template = base ++ ".tmp"
            setup = do
                    createDirectoryIfMissing True dir
                    openTempFile dir template
            cleanup (tmpfile, h) = do
                    _ <- tryIO $ hClose h
                    tryIO $ removeFile tmpfile
            use (tmpfile, h) = do
                    liftIO $ hClose h
                    a tmpfile content
                    liftIO $ rename tmpfile file

    {- Runs an action with a tmp file located in the system's tmp directory
     - (or in "." if there is none) then removes the file. -}
    withTmpFile :: (MonadIO m, MonadMask m) => Template -> (FilePath -> Handle -> m a) -> m a
    withTmpFile template a = do
            tmpdir <- liftIO $ catchDefaultIO "." getTemporaryDirectory
            withTmpFileIn tmpdir template a

    {- Runs an action with a tmp file located in the specified directory,
     - then removes the file. -}
    withTmpFileIn :: (MonadIO m, MonadMask m) => FilePath -> Template -> (FilePath -> Handle -> m a) -> m a
    withTmpFileIn tmpdir template a = bracket create remove use
      where
            create = liftIO $ openTempFile tmpdir template
            remove (name, h) = liftIO $ do
                    hClose h
                    catchBoolIO (removeFile name >> return True)
            use (name, h) = a name h

    {- It's not safe to use a FilePath of an existing file as the template
     - for openTempFile, because if the FilePath is really long, the tmpfile
     - will be longer, and may exceed the maximum filename length.
     -
     - This generates a template that is never too long.
     - (Well, it allocates 20 characters for use in making a unique temp file,
     - anyway, which is enough for the current implementation and any
     - likely implementation.)
     -}
    relatedTemplate :: FilePath -> FilePath
    relatedTemplate f
            | len > 20 = truncateFilePath (len - 20) f
            | otherwise = f
      where
            len = length f