main.nim

import winlean, os, asyncdispatch, tables, sets, strutils

type
  AlignedBuffer = tuple[base, start: pointer]

  FileEvent* = enum
    feFileCreated
    feFileRemoved
    feFileModified
    feNameChangedNew
    feNameChangedOld

  FileEventCb* = proc (
    fileName: string, 
    eventKind: FileEvent,
    bufferOverflowed: bool
  ): PFuture[void]

  WinCharBuffer {.unchecked.} = ptr array[1, TWinChar]

const
  allFileEvents* = {FileEvent.low .. FileEvent.high}


proc getPath(h: THandle, initSize = 80): string =
  var
    lastSize = initSize
    buffer = cast[WinCharBuffer](alloc0(initSize * sizeOf(TWinChar)))

  while true:
    let bufSize = GetFinalPathNameByHandle(h, buffer, initSize.Dword, 0.Dword)
    if bufSize == 0:
      osError(osLastError())
    elif bufSize > lastSize:
      buffer = resize(buffer, bufSize * sizeOf(TWinChar))
      lastSize = bufSize
      continue
    else:
      break

  result = $cast[WideCString](buffer)
  dealloc(buffer)


proc openDirHandle(path: string, followSymlink=true): TAsyncFD =
  let accessFlags = (fileShareDelete or fileShareRead or fileShareWrite)
  var modeFlags = (fileFlagBackupSemantics or fileFlagOverlapped)
  if not followSymlink:
    modeFlags = modeFlags or fileFlagOpenReparsePoint

  when useWinUnicode:
    result = createFileW(newWideCString(path), fileListDirectory, accessFlags,
                         nil, openExisting, modeFlags, 0).TAsyncFD
  else:
    result = createFileA(path, fileListDirectory, accessFlags,
                         nil, openExisting, modeFlags, 0).TAsyncFD

  if result == invalidHandleValue.TAsyncFD:
    osError(osLastError())


proc openHandle(path: string, followSymlink=true): THandle =
  var flags = FILE_FLAG_BACKUP_SEMANTICS or FILE_ATTRIBUTE_NORMAL
  if not followSymlink:
    flags = flags or FILE_FLAG_OPEN_REPARSE_POINT

  when useWinUnicode:
    result = createFileW(
      newWideCString(path), 0'i32, 
      FILE_SHARE_DELETE or FILE_SHARE_READ or FILE_SHARE_WRITE,
      nil, OPEN_EXISTING, flags, 0
      )
  else:
    result = createFileA(
      path, 0'i32, 
      FILE_SHARE_DELETE or FILE_SHARE_READ or FILE_SHARE_WRITE,
      nil, OPEN_EXISTING, flags, 0
      )
  if result == invalidHandleValue:
    osError(osLastError())


proc allocAligned(size, alignment: int): AlignedBuffer =
  ## Allocate a buffer of `size` bytes, aligned to an address that is a
  ## multiple of the given `alignment`. Note that this buffer must be freed
  ## manually!
  assert((alignment and (alignment - 1)) == 0) # Power of 2?
  var address = alloc0(size+alignment)
  if (cast[int](address) and (alignment - 1)) == 0:
    (address, address)
  else:
    let offset = alignment - (cast[int](address) and (alignment - 1))
    (address, cast[pointer](cast[int](address) + offset))


proc toFileEvent(action: dword): FileEvent =
  case action
  of FILE_ACTION_ADDED:
    result = feFileCreated
  of FILE_ACTION_REMOVED:
    result = feFileRemoved
  of FILE_ACTION_MODIFIED:
    result = feFileModified
  of FILE_ACTION_RENAMED_OLD_NAME:
    result = feNameChangedNew
  of FILE_ACTION_RENAMED_NEW_NAME:
    result = feNameChangedOld
  else:
    raise newException(EInvalidValue, "Invalid file action: " & $action)


proc toDword(actions: set[FileEvent]): dword =
  for a in actions:
    case a
    of feFileCreated:
      result = result or FILE_ACTION_ADDED
    of feFileRemoved:
      result = result or FILE_ACTION_REMOVED
    of feFileModified:
      result = result or FILE_ACTION_MODIFIED
    of feNameChangedNew:
      result = result or FILE_ACTION_RENAMED_OLD_NAME
    of feNameChangedOld:
      result = result or FILE_ACTION_RENAMED_NEW_NAME


proc cancelWatch*(handle: TAsyncFD) =
  if cancelIo(handle.THandle) == false.WinBool:
    osError(osLastError())


proc watchPathImpl(handle: TAsyncFD, callBack: FileEventCb, filterFlags: dword, 
                   bufferLen: int, watchSubdir: bool): TAsyncFD =
  ## Raw implementation that the watchDir/watchFile procedures use.
  # Note: Eventually, the file handle will need to be closed, the buffer
  # freed, and the overlapped structure manually decremented.
  let
    bufferSize = bufferLen * sizeof(FileNotifyInformation)
    buffer = allocAligned(bufferSize, 32)
    ol = PCustomOverlapped()

  proc callReadChanges: WinBool =
    result = ReadDirectoryChangesW(
      handle.THandle,
      buffer.start,
      bufferSize.int32,
      watchSubdir.WinBool,
      filterFlags,
      cast[ptr dword](nil),
      cast[POverlapped](ol),
      cast[LPOVERLAPPED_COMPLETION_ROUTINE](nil)
    )

  proc cleanupReadChanges =
    discard handle.THandle.closeHandle()
    getGlobalDispatcher().handles.excl(handle)
    buffer.base.dealloc
    GC_unref(ol)

  proc rawEventCb(sock: TAsyncFD, bytesCount: DWord, errcode: TOSErrorCode) =
    ## Raw callback for the asyncdispatch machinary to call.
    var 
      data = cast[ptr FileNotifyInformation](buffer.start)

    if errcode == ERROR_OPERATION_ABORTED.TOSErrorCode:
      cleanupReadChanges()

    while true:
      let
        offset = data.NextEntryOffset
        action = data.Action.toFileEvent()
        nameLength = data.FileNameLength
        fileName = bufferToString(data.FileName, nameLength div 2)

      discard callBack(fileName, action, false)
      if offset == 0:
        break
      data = cast[ptr FileNotifyInformation](cast[int](data) + offset)

    if callReadChanges() == WinBool(false):
      let error = osLastError()
      cleanupReadChanges()
      osError(error)

  ol.data = TCompletionData(
    sock: handle, 
    cb: rawEventCb
    )

  handle.register()
  if callReadChanges() == WinBool(false):
    let error = osLastError()
    cleanupReadChanges()
    osError(error)

  result = handle

proc watchPathImpl(path: string, callBack: FileEventCb, filterFlags: dword, 
                   bufferLen: int, watchSubdir: bool): TAsyncFD =
    result = watchPathImpl(openDirHandle(path), callBack, filterFlags,
                           bufferLen, watchSubdir)

proc watchDirectory*(path: string, callback: FileEventCb,
                     filter = allFileEvents, bufferLen = 40, 
                     watchSubdirs = false): TAsyncFD =
  if existsDir(path):
    result = watchPathImpl(path, callback, filter.toDword, bufferLen,
                           watchSubdirs)
  else:
    raise newException(EInvalidValue, path & " is not a directory")


proc watchFile*(path: string, callback: FileEventCb, filter = allFileEvents,
                bufferLen = 40, watchSubdirs = false): TAsyncFD =
  var 
    parentPath = path.expandFileName.parentDir
    targetName = extractFileName(path)
    wasRenamed = false
    newName: string
    parentHandle = openDirHandle(parentPath)
    fileHandle = openHandle(path)

  proc filterLayer(givenName: string, eventKind: FileEvent, 
                   overflowed: bool): PFuture[void] =
    template reSync =
      var newPath = getPath(fileHandle)
      newPath = newPath[4..(newPath.high)]
      echo(newPath)
      let 
        newParentPath = newPath.parentDir
      targetName = extractFileName(newPath)
      if newParentPath != parentPath:
        # We have to re-sync the path, by stopping change notifications on
        # the old directory, and re-activating them on the new directory
        cancelWatch(parentHandle)
        parentPath = newParentPath
        discard watchPathImpl(parentPath, filterLayer, filter.toDword, 
                              bufferLen, watchSubdirs)
        echo("Returning")
        return result

    var namesAreEqual: bool
    if FileSystemCaseSensitive:
      namesAreEqual = (givenName == targetName)
    else:
      namesAreEqual = (givenName.toLower == targetName.toLower)
    if namesAreEqual:
      result = callback(givenName, eventKind, overflowed)

    reSync()
  if existsFile(path):
    result = watchPathImpl(parentPath, filterLayer, filter.toDword, bufferLen, watchSubdirs)
  else:
    raise newException(EInvalidValue, path & " is not a file")



proc echoBack(name: string, event: FileEvent, overflowed: bool): PFuture[void] =
  name.echo
  event.echo
  overflowed.echo


when isMainModule:
  let handle = watchFile(r".\tests5.nim", echoBack)
  runForever()


##
## Handle, 
## addWatch
##   Add a file/directory watch to the file monitor
## removeWatch
##   Remove a file/directory watch to the file monitor
## isWatching ?
##   Determine if the path is being watched