/* ObsiGate — XLSX A1 reference helpers (#154-A5).
 *
 * Pure functions (no DOM, no i18n): safe to unit-test in Node and shared by the
 * viewer. Extracted from frontend/js/viewer.js without behaviour change.
 */

/** Parse an A1 reference ("B12") into its 1-based (row, col) parts. */
export function parseRef(ref) {
  const m = /^([A-Z]+)(\d+)$/.exec(ref || "");
  if (!m) return null;
  let col = 0;
  for (const ch of m[1]) col = col * 26 + (ch.charCodeAt(0) - 64);
  return { row: Number(m[2]), col };
}

/** Column number (1-based) → letters ("A", "Z", "AA"). */
export function columnName(col) {
  let name = "";
  while (col > 0) {
    const rem = (col - 1) % 26;
    name = String.fromCharCode(65 + rem) + name;
    col = Math.floor((col - 1) / 26);
  }
  return name;
}

// #184 — cell lookup cache. `findTd` used to run a `querySelector` per call;
// painting the grid out to A → Z × 1000 rows means a single "select column"
// asks for 26 000 cells, which was quadratic on the DOM. The index is built
// once per panel and rebuilt on demand whenever an entry no longer matches its
// own `data-cell` (the signature of a renumbered grid after a structure op).
const _cellIndex = new WeakMap();

function buildCellIndex(panel) {
  const map = new Map();
  panel.querySelectorAll("td[data-cell]").forEach((td) => {
    map.set(td.dataset.cell, td);
  });
  _cellIndex.set(panel, map);
  return map;
}

/** Drop a panel's lookup cache (bulk DOM changes). */
export function invalidateCellIndex(panel) {
  if (panel) _cellIndex.delete(panel);
}

/** Find a rendered cell inside a sheet panel by (row, col). */
export function findTd(panel, row, col) {
  const ref = `${columnName(col)}${row}`;
  const cached = _cellIndex.get(panel);
  const hit = cached && cached.get(ref);
  if (hit && hit.dataset.cell === ref) return hit;
  // Miss, or a stale entry (the row was renumbered): rebuild once and retry.
  const fresh = buildCellIndex(panel).get(ref);
  return fresh && fresh.dataset.cell === ref ? fresh : null;
}

/** Sheet prefix of a range ref ("'Mon onglet'!$A$1" → "Mon onglet"), or null. */
export function sheetOfRef(ref) {
  const s = String(ref || "");
  if (!s.includes("!")) return null;
  return s.split("!")[0].replace(/^'|'$/g, "");
}

/** First cell of a range ref ("Data!$A$1:$B$5" → "A1"), or null. */
export function firstCellOfRange(ref) {
  const s = String(ref || "");
  const body = s.includes("!") ? s.split("!").pop() : s;
  const m = /([A-Za-z]+)\$?(\d+)/.exec(body);
  return m ? `${m[1].toUpperCase()}${m[2]}` : null;
}