/**
 * Minimal RFC 4180 CSV parser for database CSV import (T-165).
 *
 * Zero dependencies (license-review rule): handles quoted fields, escaped
 * `""` quotes, and embedded commas / CRLF newlines inside quotes. The row
 * length is NOT fixed to the header (short rows pad with "", long rows keep
 * their extras) so a ragged file still maps positionally — the caller
 * decides what to do with unmatched columns.
 */

const MAX_CELLS_PER_ROW = 1000;

export function parseCsv(input: string): string[][] {
  // Tolerate a UTF-8 BOM from spreadsheet exports.
  const text = input.charCodeAt(0) === 0xfeff ? input.slice(1) : input;
  const rows: string[][] = [];
  let row: string[] = [];
  let cell = "";
  let inQuotes = false;

  for (let i = 0; i < text.length; i += 1) {
    const c = text[i];
    if (inQuotes) {
      if (c === '"') {
        if (text[i + 1] === '"') {
          cell += '"';
          i += 1;
        } else {
          inQuotes = false;
        }
      } else {
        cell += c;
      }
      continue;
    }
    if (c === '"') {
      inQuotes = true;
    } else if (c === ",") {
      row.push(cell);
      cell = "";
    } else if (c === "\n" || c === "\r") {
      if (c === "\r" && text[i + 1] === "\n") i += 1;
      row.push(cell);
      cell = "";
      rows.push(row);
      row = [];
    } else {
      cell += c;
    }
  }
  // Unterminated quote: keep what was collected (the dry run reports it).
  if (cell.length > 0 || row.length > 0) {
    row.push(cell);
    rows.push(row);
  }

  return rows.map((r) => (r.length > MAX_CELLS_PER_ROW ? r.slice(0, MAX_CELLS_PER_ROW) : r));
}