feat: troncature annoncee et lecture par fenetres des tableurs #153

- BUG-090 (#153 A8) : render_sheets() expose total_rows/total_cols,
  max_rows/max_cols et truncated ; la visionneuse affiche un bandeau
  « Feuille tronquée » (i18n FR/EN) au lieu de couper en silence, et la
  ligne d'en-têtes devient sticky (top:auto sur les numéros de ligne).
- #153 A9 : GET /api/file/{vault}/xlsx/sheet?sheet&offset&limit sert une
  fenêtre de 1 à 1000 lignes avec les vraies coordonnées A1, has_more de
  pagination et valeurs calculées A12 ; 404 feuille inconnue, 415 non-xlsx.
- Tests : TestXlsxTruncationNotice (4) + TestXlsxSheetWindow (11) avec
  contre-preuves, xlsx-viewer.test.mjs 14/14, E2E 7/7 (fixture
  sample-xlsx-large.xlsx 520 lignes), suite 1417 passed / 6 skipped,
  ruff/mypy 0, i18n parity.

🤖 Generated with Codebuff
Co-Authored-By: Codebuff <[email protected]>

backend/xlsx_reader.py

@@ -28,6 +28,12 @@ logger = logging.getLogger("obsigate.xlsx_reader")
 MAX_ROWS = 500
 MAX_COLS = 40
 
+# #153 A9 — window size served by ``read_sheet_window()`` (lazy per-sheet
+# loading). The endpoint is bounded so a single request can never ask for the
+# whole workbook back in one JSON payload; the UI pages through the rest.
+MAX_WINDOW_ROWS = 1_000
+DEFAULT_WINDOW_ROWS = 200
+
 # #153 A1 — workbook parts openpyxl does not re-serialize on load+save.
 # Verified against openpyxl 3.1.5: charts, images, drawings and pivot tables
 # DO survive the round-trip, so they are deliberately absent from this map.
@@ -98,7 +104,11 @@ def _cell_cached(cached: list[list[str]] | None, r: int, c: int) -> str:
     return row[c] if c < len(row) else ""
 
 
-def _table(grid: list[list[str]], cached: list[list[str]] | None = None) -> str:
+def _table(
+    grid: list[list[str]],
+    cached: list[list[str]] | None = None,
+    row_offset: int = 0,
+) -> str:
     """Render a grid as an HTML table.
 
     ``cached`` is the same grid read with ``data_only=True`` (#153 A12): where a
@@ -107,6 +117,10 @@ def _table(grid: list[list[str]], cached: list[list[str]] | None = None) -> str:
     number Excel last calculated instead of only the formula text. The span
     carries ``data-cached-value`` and is titled client-side from
     ``xlsx.cached_value_title`` — the backend never emits UI text.
+
+    ``row_offset`` is the number of rows skipped before this grid (#153 A9): the
+    row numbers and the ``data-cell`` references must stay the real A1
+    coordinates of the sheet, not of the window.
     """
     if not grid:
         return "<p><em>Feuille vide</em></p>"
@@ -119,7 +133,7 @@ def _table(grid: list[list[str]], cached: list[list[str]] | None = None) -> str:
     ]
     out += [f"<th>{get_column_letter(c)}</th>" for c in range(1, n_cols + 1)]
     out.append("</tr></thead><tbody>")
-    for r, row in enumerate(grid, start=1):
+    for r, row in enumerate(grid, start=row_offset + 1):
         out.append(f'<tr><th class="xlsx-rownum">{r}</th>')
         for c, val in enumerate(row, start=1):
             ref = f"{get_column_letter(c)}{r}"
@@ -191,19 +205,24 @@ def inspect_workbook(file_path: Path) -> list[str]:
         return []
 
 
-def render_sheets(file_path: Path) -> list[dict[str, str]]:
-    """Return ``[{"name": sheet_title, "html": table_html}, ...]``.
+def render_sheets(file_path: Path) -> list[dict[str, Any]]:
+    """Return one dict per sheet: ``{name, html, rows, cols, total_*, truncated}``.
 
     Reads the workbook twice: once with ``data_only=False`` for the formulas
     (what the user must edit) and, when any formula carries a cached result
     (#153 A12), once with ``data_only=True`` to show what Excel last computed.
     The second pass is skipped entirely when the archive holds no cached value,
     so the common case still costs a single load.
+
+    ``total_rows``/``total_cols`` are the dimensions the sheet declares and
+    ``truncated`` says whether the hard caps actually cut it (#153 A8) — the
+    viewer needs both to stop silently hiding the tail of a sheet.
     """
     wb = load_workbook(str(file_path), read_only=True, data_only=False)
     try:
         formulas = [_sheet_grid(ws) for ws in wb.worksheets]
         titles = [ws.title for ws in wb.worksheets]
+        extents = [_sheet_extent(ws) for ws in wb.worksheets]
     finally:
         wb.close()
 
@@ -219,16 +238,134 @@ def render_sheets(file_path: Path) -> list[dict[str, str]]:
         # shift every cached value left of its formula. Indexing it
         # positionally against the untrimmed grid keeps the two aligned.
         shadow = cached[i] if cached is not None and i < len(cached) else None
-        sheets.append({"name": title, "html": _table(grid, shadow)})
+        total_rows, total_cols = extents[i]
+        sheets.append(
+            {
+                "name": title,
+                "html": _table(grid, shadow),
+                "rows": len(grid),
+                "cols": max((len(r) for r in grid), default=0),
+                "total_rows": total_rows,
+                "total_cols": total_cols,
+                # Coverage, not display size: `rows`/`cols` are post-trim (a
+                # sheet of 3 filled cells in a 500-row block renders 1x1), and
+                # the client must announce the cap it stopped at, not how many
+                # cells happen to be non-empty.
+                "max_rows": MAX_ROWS,
+                "max_cols": MAX_COLS,
+                # A sheet is truncated when the caps, not the trailing blanks,
+                # decided its shape: comparing against the *rendered* size would
+                # flag every sheet carrying a few empty formatted rows.
+                "truncated": total_rows > MAX_ROWS or total_cols > MAX_COLS,
+            }
+        )
     return sheets
 
 
-def _sheet_grid(ws: Any) -> list[list[str]]:
-    """Read one worksheet into a grid of formatted strings, bounded by the caps."""
+def read_sheet_window(
+    file_path: Path,
+    sheet: str,
+    offset: int = 0,
+    limit: int = DEFAULT_WINDOW_ROWS,
+) -> dict[str, Any] | None:
+    """Return a window of rows of one sheet, or ``None`` if the sheet is unknown.
+
+    Backs the lazy per-sheet loading of #153 A9: the viewer asks for the rows
+    it is about to display instead of shipping every sheet in the initial file
+    payload. ``offset`` is 0-based; the row numbers and the ``data-cell``
+    references in the returned ``html`` are the real A1 coordinates of the
+    sheet, so a window is indistinguishable from a full render.
+
+    ``limit`` is clamped to :data:`MAX_WINDOW_ROWS`. Raises nothing: an unknown
+    sheet yields ``None`` and a broken workbook propagates the caller's usual
+    500.
+    """
+    offset = max(int(offset), 0)
+    limit = min(max(int(limit), 1), MAX_WINDOW_ROWS)
+
+    wb = load_workbook(str(file_path), read_only=True, data_only=False)
+    try:
+        if sheet not in wb.sheetnames:
+            return None
+        ws = wb[sheet]
+        total_rows, total_cols = _sheet_extent(ws)
+        grid = _trim(
+            _sheet_grid(ws, min_row=offset + 1, max_row=offset + limit)
+        )
+    finally:
+        wb.close()
+
+    shadow: list[list[str]] | None = None
+    # Same A12 rule as the full render: the second read only happens when the
+    # archive really holds cached results.
+    if _has_cached_values(file_path):
+        shadow = _read_cached_window(file_path, sheet, offset, limit)
+    return {
+        "sheet": sheet,
+        "offset": offset,
+        "limit": limit,
+        "rows": len(grid),
+        "cols": max((len(r) for r in grid), default=0),
+        "total_rows": total_rows,
+        "total_cols": total_cols,
+        "max_rows": MAX_ROWS,
+        "max_cols": MAX_COLS,
+        "truncated": total_rows > MAX_ROWS or total_cols > MAX_COLS,
+        "has_more": offset + len(grid) < total_rows,
+        "html": _table(grid, shadow, row_offset=offset),
+    }
+
+
+def _read_cached_window(
+    file_path: Path, sheet: str, offset: int, limit: int
+) -> list[list[str]] | None:
+    """``data_only=True`` grid for one window, or ``None`` if unavailable.
+
+    Best effort like :func:`_read_cached_grids`: a workbook Excel opens but
+    openpyxl cannot re-read must still display (formulas only).
+    """
+    try:
+        wb = load_workbook(str(file_path), read_only=True, data_only=True)
+    except Exception:
+        return None
+    try:
+        if sheet not in wb.sheetnames:
+            return None
+        return _sheet_grid(
+            wb[sheet], min_row=offset + 1, max_row=offset + limit
+        )
+    except Exception:
+        logger.debug("xlsx cached window unavailable", exc_info=True)
+        return None
+    finally:
+        wb.close()
+
+
+def _sheet_extent(ws: Any) -> tuple[int, int]:
+    """Rows and columns the worksheet declares, never negative.
+
+    ``max_row``/``max_column`` come from the sheet's dimension record; a
+    hand-edited file may omit it, hence the defensive coercion.
+    """
+    try:
+        rows = max(int(getattr(ws, "max_row", 0) or 0), 0)
+    except (TypeError, ValueError):
+        rows = 0
+    try:
+        cols = max(int(getattr(ws, "max_column", 0) or 0), 0)
+    except (TypeError, ValueError):
+        cols = 0
+    return rows, cols
+
+
+def _sheet_grid(
+    ws: Any, min_row: int = 1, max_row: int = MAX_ROWS, max_col: int = MAX_COLS
+) -> list[list[str]]:
+    """Read a worksheet window into a grid of formatted strings, bounded by the caps."""
     return [
         [_fmt(v) for v in row]
         for row in ws.iter_rows(
-            min_row=1, max_row=MAX_ROWS, max_col=MAX_COLS, values_only=True
+            min_row=min_row, max_row=max_row, max_col=max_col, values_only=True
         )
     ]