GMAIL : Moving all labels to a Sublabel.gs

/**  
 * Moves the labels under PARENT/ ;
 * set MAX_CHANGES = 1 for a test on 1 label.
 * set  PARENT       = 'MY_NEW_ROOT_FOLDER' for the new root label
 * set DRY_RUN      = true to do a dry run
 * MAX_CHANGES  = 1000;           // 1 → test on a single label ; null → all  
 *
 *
 * Copy code to https://script.google.com/
 * In Services > Add "Gmail API"
 * Run the code with the same user account than your gmail account
 */
const PARENT       = 'MY_NEW_ROOT_FOLDER';
const DRY_RUN      = false;       // true = list only, false = apply change
const MAX_CHANGES  = 1000;           // 1 → run on 1 label ; null → all labels
const SKIP_PREFIX  = ['[Gmail]', 'CATEGORY_'];
const SKIP_EXACT   = ['INBOX', 'TRASH'];

function bulkNestLabels() {
  let done = 0;                                  
  const labels = GmailApp.getUserLabels();

  for (const label of labels) {
    const oldName = label.getName();
    if (shouldSkip_(oldName)) continue;

    const newName = `${PARENT}/${oldName}`;
    if (DRY_RUN) {
      console.log(`[DRY] ${oldName} → ${newName}`);
    } else {
      Gmail.Users.Labels.update({ name: newName }, 'me', label.getId());
      console.log(`${oldName} → ${newName}`);
    }

    done++;
    if (MAX_CHANGES && done >= MAX_CHANGES) { 
      console.log(`\Stopping after ${done} change(s) (MAX_CHANGES).`);
      break;
    }
  }
}

function shouldSkip_(name) {
  if (name === PARENT || name.startsWith(PARENT + '/')) return true;
  if (SKIP_EXACT.includes(name))                     return true;
  if (SKIP_PREFIX.some(p => name.startsWith(p)))     return true;
  return false;
}