up method

String? up({ required String line, required String prefix, })

Moves to the previous (older) entry matching the active prefix, returning the line to show or null to leave the current line unchanged.

On the first step from a fresh line it captures line (to restore on the way back down) and prefix (the text before the cursor — empty browses every entry); both are supplied by the caller so prefix computation can respect the host's own character model.

Implementation

String? up({required String line, required String prefix}) {
  final entries = _history.entries;
  if (_index == 0) return null;
  if (_index == entries.length) {
    _stash = line;
    _searchPrefix = prefix;
  }
  final active = _searchPrefix ?? '';
  for (var i = _index - 1; i >= 0; i--) {
    if (entries[i].startsWith(active)) {
      _index = i;
      return entries[i];
    }
  }
  // No earlier entry matches the prefix: keep the current line.
  return null;
}