function doGet(e) {
  const ss = SpreadsheetApp.getActiveSpreadsheet();
  const sheetName = e.parameter.tab || ss.getSheets()[0].getName();
  const sheet = ss.getSheetByName(sheetName);
  if (!sheet) {
    return out({error: 'Sheet tab not found: ' + sheetName});
  }
  const data = sheet.getDataRange().getValues();
  if (data.length < 2) return out([]);
  const headers = data[0].map(h => String(h).toLowerCase()
    .replace(/\s+/g,'_').replace(/[^a-z0-9_]/g,''));
  const rows = data.slice(1)
    .filter(r => r[0] !== '' && r[0] !== null)
    .map(row => {
      const obj = {};
      headers.forEach((h,i) => { obj[h] = row[i]; });
      return obj;
    });
  return out(rows);
}
function out(data) {
  return ContentService
    .createTextOutput(JSON.stringify(data))
    .setMimeType(ContentService.MimeType.JSON);
}