{-# LANGUAGE CPP                 #-}
{-# LANGUAGE QuasiQuotes         #-}
{-# LANGUAGE ScopedTypeVariables #-}

-- | Streaming functions for interacting with the filesystem.

module System.Directory.OsPath.Streaming
  ( DirStream
  , openDirStream
  , readDirStream
  , closeDirStream
  ) where

import System.OsPath (osp)

#ifdef mingw32_HOST_OS

import Control.Concurrent.Counter (Counter)
import Control.Concurrent.Counter qualified as Counter
import Control.Monad (unless)
import System.OsPath.Types (OsPath)
import System.OsString.Internal.Types (OsString(OsString), getOsString)
import System.OsString.Windows (pstr)
import System.Win32.Types qualified as Win32
import System.Win32.WindowsString.File qualified as Win32

data DirStream = DirStream !Win32.HANDLE !Win32.FindData !Counter

openDirStream :: OsPath -> IO DirStream
openDirStream fp = do
  (h, fdat) <- Win32.findFirstFile $ getOsString fp <> [pstr|\*|]
  hasMore <- Counter.new 1 -- always at least two records, "." and ".."
  pure $! DirStream h fdat hasMore

closeDirStream :: DirStream -> IO ()
closeDirStream (DirStream h _ _) = Win32.findClose h

readDirStream :: DirStream -> IO (Maybe OsPath)
readDirStream (DirStream h fdat hasMore) = go
  where
    go = do
      hasMore' <- Counter.get hasMore
      if hasMore' /= 0
      then do
        filename  <- Win32.getFindDataFileName fdat
        hasMore'' <- Win32.findNextFile h fdat
        unless hasMore'' $
          Counter.set hasMore 0
        if filename == getOsString [osp|.|] || filename == getOsString [osp|..|]
        then go
        else pure $ Just $ OsString filename
      else pure Nothing

#else

import System.OsPath.Types (OsPath)
import System.OsString.Internal.Types (OsString(OsString), getOsString)
import System.Posix.Directory.PosixPath (DirStream, closeDirStream)
import System.Posix.Directory.PosixPath qualified as Posix

openDirStream :: OsPath -> IO DirStream
openDirStream = Posix.openDirStream . getOsString

{-# INLINE readDirStream #-}
readDirStream :: DirStream -> IO (Maybe OsPath)
readDirStream ds = go
  where
    go = do
      fp <- Posix.readDirStream ds
      case () of
        _ | fp == mempty
          -> pure Nothing
          | fp == getOsString [osp|.|] || fp == getOsString [osp|..|]
          -> go
          | otherwise
          -> pure $ Just $ OsString fp

#endif