Fix rotate and delete_pages with negative page indices

- rotate(): change `start > 0` to `start != 0` so prefix pages are
  included when a negative start index is used (e.g. start=-3)
- delete_pages(): rewrite keep-range algorithm to handle negative
  delete indices; previously all-negative inputs raised a spurious
  ValidationError instead of keeping the correct page range

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: nickwinder

src/nutrient_dws/client.py

@@ -1423,7 +1423,7 @@ async def rotate(
             end = pages.get("end", -1)
 
             # Add pages before the rotation range
-            if start > 0:
+            if start != 0:
                 part_options = cast(
                     "FilePartOptions",
                     {"pages": {"start": 0, "end": start - 1}},
@@ -1661,28 +1661,47 @@ async def delete_pages(
 
         builder = self.workflow()
 
-        # Build "keep ranges" by finding gaps between deleted indices
-        # This algorithm works with negative indices - server handles them
-        current_page = 0
+        positive_deletes = [i for i in delete_indices if i >= 0]
+        negative_deletes = [i for i in delete_indices if i < 0]
+
         page_ranges = []
+        current_page = 0
+
+        # Build keep ranges for positive delete indices
+        for delete_index in positive_deletes:
+            if current_page < delete_index:
+                page_ranges.append(
+                    normalize_page_params(
+                        {"start": current_page, "end": delete_index - 1}
+                    )
+                )
+            current_page = delete_index + 1
 
-        for delete_index in delete_indices:
-            # Skip negative indices in this calculation - they represent "from end"
-            if delete_index >= 0:
-                if current_page < delete_index:
+        if negative_deletes:
+            # Add keep range from current position up to just before the first negative delete
+            trailing_end = negative_deletes[0] - 1  # e.g. -1 -> -2, -2 -> -3
+            page_ranges.append(
+                normalize_page_params({"start": current_page, "end": trailing_end})
+            )
+            # Add keep ranges between consecutive negative delete indices
+            for i in range(len(negative_deletes) - 1):
+                between_start = negative_deletes[i] + 1
+                between_end = negative_deletes[i + 1] - 1
+                if between_start <= between_end:
                     page_ranges.append(
                         normalize_page_params(
-                            {"start": current_page, "end": delete_index - 1}
+                            {"start": between_start, "end": between_end}
                         )
                     )
-                current_page = delete_index + 1
-
-        # Add remaining pages to end (use -1 for last page) add if we have positive indices processed
-        if (
-            current_page >= 0
-            and len(delete_indices) > 0
-            and any(i >= 0 for i in delete_indices)
-        ):
+            # Add keep range after the last negative delete, if it isn't the last page
+            if negative_deletes[-1] != -1:
+                page_ranges.append(
+                    normalize_page_params(
+                        {"start": negative_deletes[-1] + 1, "end": -1}
+                    )
+                )
+        else:
+            # All deletes are positive: keep remaining pages to end of document
             page_ranges.append(
                 normalize_page_params({"start": current_page, "end": -1})
             )

tests/unit/test_client.py

@@ -1202,3 +1202,111 @@ async def test_ocr_with_iso_language_codes(
         mock_workflow_instance.add_file_part.assert_called_once_with(
             file, None, [{"type": "ocr", "language": ["eng", "deu", "fra"]}]
         )
+
+
+class TestNutrientClientRotate:
+    """Tests for NutrientClient rotate functionality."""
+
+    def _make_mock_workflow(self, mock_staged_workflow_builder):
+        mock_workflow_instance = MagicMock()
+        mock_output_stage = MagicMock()
+        mock_output_stage.execute = AsyncMock(
+            return_value={
+                "success": True,
+                "output": {
+                    "buffer": b"test-buffer",
+                    "mimeType": "application/pdf",
+                    "filename": "output.pdf",
+                },
+            }
+        )
+        mock_workflow_instance.add_file_part.return_value = mock_workflow_instance
+        mock_workflow_instance.output_pdf.return_value = mock_output_stage
+        mock_staged_workflow_builder.return_value = mock_workflow_instance
+        return mock_workflow_instance
+
+    @patch("nutrient_dws.client.StagedWorkflowBuilder")
+    @pytest.mark.asyncio
+    async def test_rotate_with_negative_start_includes_prefix_pages(
+        self, mock_staged_workflow_builder, unit_client
+    ):
+        """Rotating last N pages with negative start must keep all preceding pages."""
+        mock_workflow = self._make_mock_workflow(mock_staged_workflow_builder)
+
+        await unit_client.rotate("document.pdf", 90, {"start": -3, "end": -1})
+
+        # Expect 2 add_file_part calls: prefix pages then rotated pages
+        assert mock_workflow.add_file_part.call_count == 2
+        # First call: prefix pages before the rotation range (pages 0 to -4)
+        first_call_pages = mock_workflow.add_file_part.call_args_list[0][0][1]
+        assert first_call_pages == {"pages": {"start": 0, "end": -4}}
+        # Second call: the rotated range with the rotate action
+        second_call_pages = mock_workflow.add_file_part.call_args_list[1][0][1]
+        assert second_call_pages == {"pages": {"start": -3, "end": -1}}
+
+
+class TestNutrientClientDeletePages:
+    """Tests for NutrientClient delete_pages functionality."""
+
+    def _make_mock_workflow(self, mock_staged_workflow_builder):
+        mock_workflow_instance = MagicMock()
+        mock_output_stage = MagicMock()
+        mock_output_stage.execute = AsyncMock(
+            return_value={
+                "success": True,
+                "output": {
+                    "buffer": b"test-buffer",
+                    "mimeType": "application/pdf",
+                    "filename": "output.pdf",
+                },
+            }
+        )
+        mock_workflow_instance.add_file_part.return_value = mock_workflow_instance
+        mock_workflow_instance.output_pdf.return_value = mock_output_stage
+        mock_staged_workflow_builder.return_value = mock_workflow_instance
+        return mock_workflow_instance
+
+    @patch("nutrient_dws.client.StagedWorkflowBuilder")
+    @pytest.mark.asyncio
+    async def test_delete_last_page_using_negative_index(
+        self, mock_staged_workflow_builder, unit_client
+    ):
+        """delete_pages([-1]) must keep all pages except the last, not raise an error."""
+        mock_workflow = self._make_mock_workflow(mock_staged_workflow_builder)
+
+        result = await unit_client.delete_pages("document.pdf", [-1])
+
+        assert result["buffer"] == b"test-buffer"
+        assert mock_workflow.add_file_part.call_count == 1
+        kept_pages = mock_workflow.add_file_part.call_args_list[0][0][1]
+        assert kept_pages == {"pages": {"start": 0, "end": -2}}
+
+    @patch("nutrient_dws.client.StagedWorkflowBuilder")
+    @pytest.mark.asyncio
+    async def test_delete_multiple_pages_using_only_negative_indices(
+        self, mock_staged_workflow_builder, unit_client
+    ):
+        """delete_pages([-2, -1]) must keep all pages except the last two."""
+        mock_workflow = self._make_mock_workflow(mock_staged_workflow_builder)
+
+        result = await unit_client.delete_pages("document.pdf", [-2, -1])
+
+        assert result["buffer"] == b"test-buffer"
+        assert mock_workflow.add_file_part.call_count == 1
+        kept_pages = mock_workflow.add_file_part.call_args_list[0][0][1]
+        assert kept_pages == {"pages": {"start": 0, "end": -3}}
+
+    @patch("nutrient_dws.client.StagedWorkflowBuilder")
+    @pytest.mark.asyncio
+    async def test_delete_pages_with_mixed_positive_and_negative_indices(
+        self, mock_staged_workflow_builder, unit_client
+    ):
+        """delete_pages([0, -1]) must keep middle pages, not include the deleted last page."""
+        mock_workflow = self._make_mock_workflow(mock_staged_workflow_builder)
+
+        result = await unit_client.delete_pages("document.pdf", [0, -1])
+
+        assert result["buffer"] == b"test-buffer"
+        assert mock_workflow.add_file_part.call_count == 1
+        kept_pages = mock_workflow.add_file_part.call_args_list[0][0][1]
+        assert kept_pages == {"pages": {"start": 1, "end": -2}}