priorProcName := EventList.Remove(eventHandle, "").UserDefinedProc.Name

#NoEnv
SetBatchLines -1

OnDirectoryChanges(A_ScriptDir, "Test0")
OnDirectoryChanges(A_Desktop, "Test1")

Test0(filePath, action) {
    MsgBox % A_ThisFunc . "`n" . ["Added", "Removed", "Modified", "Renamed, old name", "Renamed, new name"][action] ": " filePath
}

Test1(filePath, action) {
    MsgBox % A_ThisFunc . "`n" . ["Added", "Removed", "Modified", "Renamed, old name", "Renamed, new name"][action] ": " filePath
}

OnDirectoryChanges(dirPath, procName := -1, notifyFilter := 3) {
    static DirList := {}
    static EventList
    static AHK_ReadDirectoryChanges := DllCall("RegisterWindowMessage", "Str", "AHK_ReadDirectoryChanges", "UInt")

    IsObject(EventList) || EventList := DirectoryChangesEventListener(-1, 0, 0)

    if (procName = -1) {
        return EventList[DirList[dirPath]].UserDefinedProc.Name
    }

    else if (procName = "") {
        if DirList.HasKey(dirPath) && eventHandle := DirList.Remove(dirPath)
            return EventList.Remove(eventHandle).UserDefinedProc.Name
    }

    else if IsFunc(procName) {
        if DirList.HasKey(dirPath) && eventHandle := DirList.Remove(dirPath)
            priorProcName := EventList.Remove(eventHandle).UserDefinedProc.Name
        else priorProcName := procName

        if OnMessage(AHK_ReadDirectoryChanges) != "DirectoryChangesEventListener"
            OnMessage(AHK_ReadDirectoryChanges, "DirectoryChangesEventListener", 30)

        Event := new _Event
        Event.Proc := new _AsyncReadDirectoryChanges(dirPath, notifyFilter)
        Event.Wait := new _AsyncWaitFunc(Event.handle, A_ScriptHWND, AHK_ReadDirectoryChanges)
        Event.UserDefinedProc := Func(procName)
        Event.dirPath := dirPath

        DirList[dirPath] := Event.handle
        EventList[Event.handle] := Event

        Event.Proc()
        Event.Wait()

        return priorProcName
    }
    else return false
}

DirectoryChangesEventListener(wParam, lParam, msg) {
    static EventList := {}
    static AHK_ReadDirectoryChanges := DllCall("RegisterWindowMessage", "Str", "AHK_ReadDirectoryChanges", "UInt")

    if (msg = AHK_ReadDirectoryChanges && Event := EventList[wParam]) {
        action := Event.Proc.GetEventType()
        name := Event.Proc.GetObjectName()
        path := Event.dirPath . "\" . name
        Proc := Event.UserDefinedProc
        %Proc%(path, action)

        Event.Proc()
        Event.Wait()
    }
    else if (wParam = -1)
        return EventList
}

class _Event
{
    __New() {
        this.SetCapacity(6)

        if !this.handle := DllCall("CreateEvent", "Int", 0, "Int", 0, "Int", 1, "Int", 0, "Ptr")
            Throw Exception("Failed to create new event.`n`nError code:`t" . A_LastError)

        if !ObjSetCapacity(this, "overlapped", 32)
            Throw Exception("Failed to allocate memory for overlapped structure`n`nErrorLevel:`t" . ErrorLevel)

        if !NumPut(this.handle, 0+ObjGetAddress(this, "overlapped"), A_PtrSize*2+8, "ptr")
            Throw Exception("Failed to create overlapped structure.`n`nErrorLevel:`t" . ErrorLevel)
    }

    __Delete() {
        if !DllCall("CloseHandle", "Ptr", this.handle, "UInt")
            Throw Exception("Failed to close event handle.`n`nError code:`t" . A_LastError)
    }
}

class _AsyncWaitFunc
{
    __New(eventObjHandle, hWnd, msg, timeout := -1) {
        this.SetCapacity(1)

        if !this.startAddress := CreateWaitFunc(eventObjHandle, hWnd, msg, timeout)
            Throw Exception("Failed to create wait function.`n`nError code:`t" . A_LastError)
    }

    __Call(EventObj) {
        if IsObject(EventObj) {
            if !threadHandle := DllCall("CreateThread", "Int", 0, "Int", 0, "Ptr", 0|this.startAddress, "Int", 0, "UInt", 0, "Int", 0, "Ptr")
                Throw Exception("Failed to create thread.`n`nError code:`t" . A_LastError)

            return threadHandle
        }
    }

    __Delete() {
        FreeWaitFunc(this.startAddress)
    }
}

class _AsyncReadDirectoryChanges
{
    __New(dirPath, notifyFilter) {
        this.SetCapacity(3)
        this.notifyFilter := notifyFilter

        if !this.handle := DllCall("CreateFile", "Str", dirPath, "UInt", 1, "UInt", 3, "Int", 0, "UInt", 3, "UInt", 0x42000000, "Int", 0, "Ptr")
            Throw Exception("Failed to open specified path.`n`nError code:`t" . A_LastError)

        if !ObjSetCapacity(this, "buffer", 1024)
            Throw Exception("Failed to set ReadDirectoryChangesW output buffer size`n`nErrorLevel:`t" . ErrorLevel)
    }

    GetEventType() {
        if !bufferRef := ObjGetAddress(this, "buffer")
            Throw Exception("Failed to get ReadDirectoryChangesW output buffer address`n`nErrorLevel:`t" . ErrorLevel)

        return NumGet(0+bufferRef, 4,  "UInt")
    }

    GetObjectName() {
        if !bufferRef := ObjGetAddress(this, "buffer")
            Throw Exception("Failed to get ReadDirectoryChangesW output buffer address`n`nErrorLevel:`t" . ErrorLevel)

        return StrGet(bufferRef+12, NumGet(0+bufferRef, 8, "UInt")//2)
    }

    __Call(EventObj) {
        if IsObject(EventObj) {
            if !bufferRef := ObjGetAddress(this, "buffer")
                Throw Exception("Failed to get ReadDirectoryChangesW output buffer address`n`nErrorLevel:`t" . ErrorLevel)

            if !overlappedStructRef := ObjGetAddress(EventObj, "overlapped")
                Throw Exception("Failed to get ReadDirectoryChangesW overlapped struct address`n`nErrorLevel:`t" . ErrorLevel)

            return DllCall("ReadDirectoryChangesW"
                , "Ptr", this.handle
                , "Ptr", bufferRef
                , "UInt", 1024
                , "Int", 1
                , "UInt", this.notifyFilter
                , "UInt", 0
                , "Ptr", overlappedStructRef
                , "Int", 0)
        }
    }

    __Delete() {
        if !DllCall("CloseHandle", "Ptr", this.handle, "UInt")
            Throw Exception("Failed to close directory handle.`n`nError code:`t" . A_LastError)
    }

}

FreeWaitFunc(ptr)
{
    global __Free__
    __Free__.Insert(ptr)
}

CreateWaitFunc(Handle, hWnd, Msg, Timeout := -1)
{
    static __PageSize__, __Offset__, __Ptr__, __PageNum__
    global __Free__

    if((!__Offset__)||((__PageSize__-__Offset__<(A_PtrSize = 4 ? 49 : 85))&&(!__Free__.MaxIndex())))
    {
        if(!__Ptr__)
        {
            __Ptr__ := Array()
            __Free__ := Array()
        }
        __PageNum__++
        VarSetCapacity(FuncName, 0x30, 0)
        __Ptr__[__PageNum__] := DllCall("VirtualAlloc", "ptr", 0, "ptr", 1, "uint", 0x1000, "uint", 0x40, "ptr")
        DllCall("VirtualQuery", "ptr", 0|__Ptr__[__PageNum__], "ptr", &FuncName, "ptr", 0x30)
        __PageSize__ := NumGet(&FuncName, 3*A_PtrSize, "ptr")
        StrPut("WaitForSingleObject", &FuncName, 0x30, "CP1250")
        NumPut(DllCall("GetProcAddress", "ptr", DllCall("GetModuleHandle", "str", "kernel32.dll"), "ptr", &FuncName, "ptr"), 0|__Ptr__[__PageNum__], 0, "ptr")
        StrPut("PostMessageW", &FuncName, 0x30, "CP1250")
        NumPut(DllCall("GetProcAddress", "ptr", DllCall("GetModuleHandle", "str", "user32.dll"), "ptr", &FuncName, "ptr"), 0|__Ptr__[__PageNum__], A_PtrSize, "ptr")
        __Offset__ := 2*A_PtrSize
    }
    if(!__Free__.MaxIndex())
    {
        ptr := __Ptr__[__PageNum__]+__Offset__
        __Offset__+=(A_PtrSize = 4 ? 49 : 85)
    }
    else
        ptr := __Free__.Remove(1)
    if(A_PtrSize=4)
    {
        NumPut(0x68, 0|ptr, 0, "uchar")
        NumPut(Timeout, 0|ptr, 1, "uint")
        NumPut(0x68, 0|ptr, 5, "uchar")
        NumPut(Handle, 0|ptr, 6, "ptr")
        NumPut(0x15FF, 0|ptr, 10, "ushort")
        NumPut(0|__Ptr__[__PageNum__], 0|ptr, 12, "ptr")
        NumPut(0x50, 0|ptr, 16, "uchar")
        NumPut(0x68, 0|ptr, 17, "uchar")
        NumPut(Handle, 0|ptr, 18, "ptr")
        NumPut(0x68, 0|ptr, 22, "uchar")
        NumPut(Msg, 0|ptr, 23, "uint")
        NumPut(0x68, 0|ptr, 27, "uchar")
        NumPut(hWnd, 0|ptr, 28, "ptr")
        NumPut(0x15FF, 0|ptr, 32, "ushort")
        NumPut(0|__Ptr__[__PageNum__]+4, 0|ptr, 34, "ptr")
        NumPut(0xC2, 0|ptr, 38, "uchar")
        NumPut(4, 0|ptr, 39, "ushort")
    }
    else
    {
        NumPut(0x53, 0|ptr, 0, "uchar")
        NumPut(0x20EC8348, 0|ptr, 1, "uint")
        NumPut(0xBACB8948, 0|ptr, 5, "uint")
        NumPut(Timeout, 0|ptr, 9, "uint")
        NumPut(0xB948, 0|ptr, 13, "ushort")
        NumPut(Handle, 0|ptr, 15, "ptr")
        NumPut(0x15FF, 0|ptr, 23, "ushort")
        NumPut(-29-(ptr-__Ptr__[__PageNum__]), 0|ptr, 25, "uint")
        NumPut(0xB849, 0|ptr, 29, "ushort")
        NumPut(Handle, 0|ptr, 31, "ptr")
        NumPut(0xBA, 0|ptr, 39, "uchar")
        NumPut(Msg, 0|ptr, 40, "uint")
        NumPut(0xB948, 0|ptr, 44, "ushort")
        NumPut(hWnd, 0|ptr, 46, "ptr")
        NumPut(0xC18941, 0|ptr, 54, "uint")
        NumPut(0x15FF, 0|ptr, 57, "ushort")
        NumPut(-55-(ptr-__Ptr__[__PageNum__]), 0|ptr, 59, "uint")
        NumPut(0x20C48348, 0|ptr, 63, "uint")
        NumPut(0x5B, 0|ptr, 67, "uchar")
        NumPut(0xC3, 0|ptr, 68, "uchar")
    }
    return ptr
}