let _xlsx: typeof import("xlsx") | null = null;

async function getXLSX() {
  if (!_xlsx) {
    _xlsx = await import("xlsx");
  }
  return _xlsx;
}

/**
 * Parse an Excel (.xlsx, .xls) or CSV file to an array of row objects.
 * Keys come from the first row (headers).
 */
export async function parseSpreadsheet(file: File): Promise<Record<string, string>[]> {
  const XLSX = await getXLSX();
  const buffer = await file.arrayBuffer();
  const data = new Uint8Array(buffer);
  const workbook = XLSX.read(data, { type: "array" });
  const sheetName = workbook.SheetNames[0];
  if (!sheetName) {
    return [];
  }
  const sheet = workbook.Sheets[sheetName];
  if (!sheet) {
    return [];
  }
  return XLSX.utils.sheet_to_json<Record<string, string>>(sheet, {
    raw: false,
    defval: "",
  });
}

export function isSpreadsheetFile(file: File): boolean {
  return (
    file.type === "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet" ||
    file.type === "application/vnd.ms-excel" ||
    file.name.endsWith(".xlsx") ||
    file.name.endsWith(".xls") ||
    file.name.endsWith(".csv")
  );
}