function sendDailyFollowUpReminder() {
  const sheetName = 'Leads';
  const recipient = Session.getActiveUser().getEmail();
  const sheet = SpreadsheetApp.getActive().getSheetByName(sheetName);
  if (!sheet) throw new Error('Missing sheet: ' + sheetName);

  const values = sheet.getDataRange().getValues();
  const headers = values.shift();
  const index = Object.fromEntries(headers.map((name, i) => [String(name).trim(), i]));
  const today = new Date();
  today.setHours(0, 0, 0, 0);

  const dueRows = values.filter((row) => {
    const rawDate = row[index.next_follow_up_date];
    if (!rawDate) return false;
    const followUpDate = new Date(rawDate);
    followUpDate.setHours(0, 0, 0, 0);
    const stage = String(row[index.lead_stage] || '').toLowerCase();
    return followUpDate <= today && !['closed won', 'closed lost', 'not a fit'].includes(stage);
  });

  if (!dueRows.length) return;

  const lines = dueRows.map((row) => [
    row[index.lead_name],
    row[index.company],
    row[index.next_action],
    row[index.next_follow_up_date],
    row[index.notes],
  ].filter(Boolean).join(' | '));

  MailApp.sendEmail({
    to: recipient,
    subject: 'Lead follow-ups due today',
    body: 'Follow up on these leads today:\n\n' + lines.join('\n'),
  });
}