"""Minimal read-only XLSX reader (stdlib only): sheet -> list of rows of strings."""

from __future__ import annotations

import io
import re
import zipfile
import xml.etree.ElementTree as ET

_NS = {"m": "http://schemas.openxmlformats.org/spreadsheetml/2006/main",
       "r": "http://schemas.openxmlformats.org/officeDocument/2006/relationships"}
_T = "{%s}t" % _NS["m"]


def _col_index(ref: str) -> int:
    letters = re.match(r"[A-Z]+", ref).group(0)
    n = 0
    for ch in letters:
        n = n * 26 + (ord(ch) - 64)
    return n - 1


def read_sheet(data: bytes, sheet: str | int = 0) -> list[list[str]]:
    z = zipfile.ZipFile(io.BytesIO(data))
    shared: list[str] = []
    if "xl/sharedStrings.xml" in z.namelist():
        for si in ET.fromstring(z.read("xl/sharedStrings.xml")).findall("m:si", _NS):
            shared.append("".join(t.text or "" for t in si.iter(_T)))
    wb = ET.fromstring(z.read("xl/workbook.xml"))
    sheets = [s for s in wb.find("m:sheets", _NS)]
    if isinstance(sheet, str):
        idx = next(i for i, s in enumerate(sheets) if s.get("name") == sheet)
    else:
        idx = sheet
    rid = sheets[idx].get("{%s}id" % _NS["r"])
    rels = ET.fromstring(z.read("xl/_rels/workbook.xml.rels"))
    target = next(r.get("Target") for r in rels if r.get("Id") == rid)
    path = "xl/" + target.lstrip("/").removeprefix("xl/")
    root = ET.fromstring(z.read(path))
    rows: list[list[str]] = []
    for r in root.find("m:sheetData", _NS).findall("m:row", _NS):
        cells: dict[int, str] = {}
        for c in r.findall("m:c", _NS):
            v = c.find("m:v", _NS)
            if v is None:
                inline = c.find("m:is", _NS)
                text = "".join(t.text or "" for t in inline.iter(_T)) if inline is not None else ""
            else:
                text = shared[int(v.text)] if c.get("t") == "s" else (v.text or "")
            cells[_col_index(c.get("r"))] = text
        width = max(cells) + 1 if cells else 0
        rows.append([cells.get(i, "") for i in range(width)])
    return rows