"""Render ``.xlsx`` workbooks as HTML tables for the viewer (#xlsx).

Read-only: formulas are shown as their text (``data_only=False``) so a
round-trip through the viewer never depends on Excel's cached values.
Write-side lives in ``backend.services.mutations.edit_xlsx_cells``.

:func:`inspect_workbook` lists the workbook features that an openpyxl
round-trip would drop (#153 A1) so the UI can warn before saving.
"""

from __future__ import annotations

import html
import re
import zipfile
from datetime import date, datetime
from pathlib import Path
from typing import Any

from openpyxl import load_workbook
from openpyxl.utils import get_column_letter

# ponytail: hard caps bound the rendered grid (500 rows x 40 cols per sheet).
# Raise them, or paginate per sheet, if a real workbook needs more.
MAX_ROWS = 500
MAX_COLS = 40

# #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.
LOSSY_PARTS: dict[str, tuple[str, ...]] = {
    "slicers": ("xl/slicers/", "xl/slicerCaches/", "xl/timelines/"),
    "form_controls": ("xl/ctrlProps/", "xl/activeX/"),
    "connections": ("xl/queryTables/", "xl/connections.xml"),
    "custom_xml": ("customXml/",),
    "signature": ("_xmlsignatures/",),
    "rich_comments": ("xl/threadedComments/", "xl/persons/"),
    "macros": ("xl/vbaProject.bin",),
}

# A formula cell carrying its last computed result: ``<f>…</f><v>…</v>``.
# openpyxl writes an EMPTY ``<v></v>`` itself, hence the ``[^<]`` guard: only a
# non-empty value counts. openpyxl keeps the formula but drops the cached result,
# so any reader using ``data_only=True`` (pandas, converters) sees ``None`` until
# Excel recalculates.
_CACHED_FORMULA_RE = re.compile(rb"<f[ >][^<]*</f>\s*<v>[^<]")

# Sheet XML scanned by the cached-formula probe (CPU guard, like MAX_REPLACE_FILE_BYTES).
_MAX_PROBE_BYTES = 8_000_000


def _fmt(value: Any) -> str:
    if value is None:
        return ""
    if isinstance(value, datetime):
        return value.strftime("%Y-%m-%d %H:%M")
    if isinstance(value, date):
        return value.isoformat()
    return str(value)


def _trim(grid: list[list[str]]) -> list[list[str]]:
    """Drop trailing empty rows and columns (openpyxl pads to max_col)."""
    while grid and not any(grid[-1]):
        grid.pop()
    if not grid:
        return grid
    width = 0
    for row in grid:
        for i in range(len(row) - 1, -1, -1):
            if row[i]:
                width = max(width, i + 1)
                break
    return [row[:width] for row in grid]


def _table(grid: list[list[str]]) -> str:
    if not grid:
        return "<p><em>Feuille vide</em></p>"
    n_cols = max(len(row) for row in grid)
    out = [
        (
            '<div class="csv-table-wrapper"><table class="csv-table xlsx-table">'
            '<thead><tr><th class="xlsx-corner"></th>'
        )
    ]
    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):
        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}"
            out.append(f'<td data-cell="{ref}">{html.escape(val)}</td>')
        out.append("</tr>")
    out.append("</tbody></table></div>")
    return "".join(out)


def _has_cached_formulas(zf: zipfile.ZipFile) -> bool:
    """True when at least one formula cell still carries its computed value."""
    budget = _MAX_PROBE_BYTES
    for name in zf.namelist():
        if not name.startswith("xl/worksheets/sheet") or not name.endswith(".xml"):
            continue
        try:
            with zf.open(name) as fh:
                while budget > 0:
                    chunk = fh.read(65536)
                    if not chunk:
                        break
                    budget -= len(chunk)
                    if _CACHED_FORMULA_RE.search(chunk):
                        return True
        except (KeyError, OSError, zipfile.BadZipFile):
            continue
    return False


def inspect_workbook(file_path: Path) -> list[str]:
    """Return the sorted keys of :data:`LOSSY_PARTS` present in *file_path*.

    Read-only inspection of the OPC package (central directory + a bounded scan
    of the sheet XML). Never raises: an unreadable or encrypted workbook simply
    yields ``[]`` and the save path keeps its current behaviour.

    ``cached_values`` is a synthetic key: openpyxl keeps the formula but drops
    the cached result, so the workbook stays correct once Excel recalculates it.
    """
    try:
        with zipfile.ZipFile(file_path) as zf:
            names = set(zf.namelist())
            found = {
                key
                for key, prefixes in LOSSY_PARTS.items()
                if any(name.startswith(prefix) for name in names for prefix in prefixes)
            }
            if _has_cached_formulas(zf):
                found.add("cached_values")
            return sorted(found)
    except (OSError, zipfile.BadZipFile):
        return []


def render_sheets(file_path: Path) -> list[dict[str, str]]:
    """Return ``[{"name": sheet_title, "html": table_html}, ...]``."""
    wb = load_workbook(str(file_path), read_only=True, data_only=False)
    try:
        sheets = []
        for ws in wb.worksheets:
            grid = [
                [_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
                )
            ]
            sheets.append({"name": ws.title, "html": _table(_trim(grid))})
        return sheets
    finally:
        wb.close()