public function store(Request $request)
    {
        $this->validate($request, [
            'title' => 'required|string',
            'amount' => 'required|numeric',
            'cover' => 'image|mimes:jpg,png,jpeg|max:1024',
            'author_id' => 'required|exists:authors,id',
        ]);
        $books = Book::create($request->except('cover'));
        if ($request->hasFile('cover')) {
            $uploaded_cover = $request->file('cover');
            $extension = $uploaded_cover->getClientOriginalExtension();
            $filename = md5(time()) . '.' . $extension;
            $destinationPath = public_path() . DIRECTORY_SEPARATOR . 'images';
            $uploaded_cover->move($destinationPath, $filename);
            $books->cover = $filename;
            $books->save();
        }
        return redirect()->route('books.index');
    }