feat: add native Excel parsing and improve Google Drive content extraction

- Introduced a new utility for parsing .xlsx files into markdown format, enhancing the ability to process Excel documents natively.
- Updated the Google Drive content extractor to utilize the new Excel parsing functionality, allowing for better handling of spreadsheet files.
- Enhanced file type detection and export logic to support various document formats, improving overall content extraction accuracy.
- Added unit tests to ensure the correctness of the new Excel parsing feature and its integration with existing content extraction workflows.

surfsense_backend/tests/unit/test_office_parsers.py

@@ -0,0 +1,129 @@
+"""Unit tests for native Office file parsers (no DB, no external services)."""
+
+import tempfile
+
+import pytest
+from openpyxl import Workbook
+
+pytestmark = pytest.mark.unit
+
+
+# ---------------------------------------------------------------------------
+# Helpers
+# ---------------------------------------------------------------------------
+
+
+def _create_xlsx(sheets: dict[str, list[list]]) -> str:
+    """Create a real .xlsx file on disk and return its path.
+
+    ``sheets`` maps sheet name -> list of rows, where each row is a list of
+    cell values.
+    """
+    wb = Workbook()
+    first = True
+    for name, rows in sheets.items():
+        ws = wb.active if first else wb.create_sheet(title=name)
+        if first:
+            ws.title = name
+            first = False
+        for row in rows:
+            ws.append(row)
+    tmp = tempfile.NamedTemporaryFile(suffix=".xlsx", delete=False)
+    wb.save(tmp.name)
+    wb.close()
+    tmp.close()
+    return tmp.name
+
+
+# ---------------------------------------------------------------------------
+# Tracer bullet: cell values appear in markdown
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.asyncio
+async def test_parse_excel_produces_markdown_with_cell_values():
+    """A single-sheet .xlsx with known data produces markdown containing those values."""
+    from app.utils.office_parsers import parse_excel_to_markdown
+
+    path = _create_xlsx(
+        {"Sales": [["Product", "Revenue"], ["Widget", 1500], ["Gadget", 3200]]}
+    )
+
+    md = await parse_excel_to_markdown(path, filename="report.xlsx")
+
+    assert "Product" in md
+    assert "Revenue" in md
+    assert "Widget" in md
+    assert "1500" in md
+    assert "Gadget" in md
+    assert "3200" in md
+    assert "report.xlsx" in md
+    assert "|" in md
+
+
+# ---------------------------------------------------------------------------
+# Multi-sheet workbooks include all sheets
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.asyncio
+async def test_parse_excel_includes_all_sheets():
+    """Both sheet names and their data appear in the output."""
+    from app.utils.office_parsers import parse_excel_to_markdown
+
+    path = _create_xlsx(
+        {
+            "Inventory": [["Item", "Qty"], ["Bolts", 200]],
+            "Pricing": [["Item", "Price"], ["Bolts", 4.50]],
+        }
+    )
+
+    md = await parse_excel_to_markdown(path, filename="multi.xlsx")
+
+    assert "Inventory" in md
+    assert "Pricing" in md
+    assert "Bolts" in md
+    assert "200" in md
+    assert "4.5" in md
+
+
+# ---------------------------------------------------------------------------
+# Empty spreadsheet raises ValueError
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.asyncio
+async def test_parse_excel_raises_on_empty_file():
+    """An .xlsx with no data raises ValueError."""
+    from app.utils.office_parsers import parse_excel_to_markdown
+
+    wb = Workbook()
+    tmp = tempfile.NamedTemporaryFile(suffix=".xlsx", delete=False)
+    wb.save(tmp.name)
+    wb.close()
+    tmp.close()
+
+    with pytest.raises(ValueError, match="No data found"):
+        await parse_excel_to_markdown(tmp.name, filename="empty.xlsx")
+
+
+# ---------------------------------------------------------------------------
+# _parse_file_to_markdown routes .xlsx natively (no ETL call)
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.asyncio
+async def test_parse_file_to_markdown_routes_xlsx_natively():
+    """content_extractor._parse_file_to_markdown uses native parser for .xlsx."""
+    from app.connectors.google_drive.content_extractor import _parse_file_to_markdown
+
+    path = _create_xlsx(
+        {"Data": [["Name", "Score"], ["Alice", 95], ["Bob", 82]]}
+    )
+
+    md = await _parse_file_to_markdown(path, "grades.xlsx")
+
+    assert "Alice" in md
+    assert "95" in md
+    assert "Bob" in md
+    assert "82" in md