gistfile1.txt

        validation(with: {form: true}) do
          configure do
            def non_destroyed_items?(value)
              form.items.detect {|i| !i._destroy}
            end

            def item_sum?(value)
              isum = form.items.reduce(0) do |sum, item| 
                sum += item._destroy ? 0 : item.amount
              end

              isum == value
            end
          end

          required(:date).filled(:date?)
          required(:amount).filled(:int?, :item_sum?, not_eql?: 0)

          required(:items).value(type?: Array, non_destroyed_items?: true) do
            each do
              schema do
                optional(:_destroy).maybe(:bool?)
                optional(:id).maybe(:int?)
                required(:bucket).filled
                required(:amount).filled(:int?)
              end
            end
          end
        end