def create
  add_more_images(images_params[:images])
  flash[:error] = "Failed uploading images" unless @item.save
  redirect_to admin_items_path
end

def destroy
  remove_image_at_index(params[:id].to_i)
  flash[:error] = "Failed deleting image" unless @item.save
  redirect_to admin_items_path
end

def add_more_images(new_images)
  images = @item.images
  images += new_images
  @item.images = images
end

def remove_image_at_index(index)
  remain_images = @item.images # copy the array
  deleted_image = remain_images.delete_at(index) # delete the target image
  deleted_image.try(:remove!) # delete image from S3
  @item.images = remain_images # re-assign back
end