resolveSessionDir function

String? resolveSessionDir({ Directory? start, })

Auto-locate the session directory by walking up from start (defaults to CWD) looking for an existing .fdb/ directory whose PID file points at a live process.

Walk stops at $HOME or the filesystem root, whichever comes first.

• If a live .fdb/ is found in a parent of start, logs one INFO: line to stderr so the user knows which directory was picked.
• If no live .fdb/ is found anywhere, returns null and leaves _sessionDir at the CWD default so commands like status can handle the missing-session case themselves.

Returns the resolved session-dir path, or null if no live session was found.

Implementation

String? resolveSessionDir({Directory? start}) {
  final cwd = (start ?? Directory.current).absolute.path;
  final home = Platform.environment['HOME'] ?? '/';

  var current = Directory(cwd);

  while (true) {
    final candidate = Directory('${current.path}/$sessionDirName');
    if (candidate.existsSync()) {
      final pidPath = '${candidate.path}/fdb.pid';
      final pidFile = File(pidPath);
      bool alive;
      if (pidFile.existsSync()) {
        final raw = pidFile.readAsStringSync().trim();
        final pid = int.tryParse(raw);
        if (pid != null) {
          try {
            alive = Process.runSync('kill', ['-0', pid.toString()]).exitCode == 0;
          } catch (_) {
            alive = false;
          }
        } else {
          alive = false;
        }
      } else {
        // No PID file — only treat as a valid candidate if a vm_uri.txt
        // exists, indicating an interrupted launch that left a recoverable
        // VM service session. A bare .fdb/ with neither file is a leftover
        // directory that should not attract walk-up resolution.
        alive = File('${candidate.path}/vm_uri.txt').existsSync();
      }

      if (alive) {
        final resolved = candidate.absolute.path;
        if (resolved != Directory('$cwd/$sessionDirName').absolute.path) {
          stderr.writeln('INFO: Using session dir from ${current.path}');
        }
        _sessionDir = resolved;
        return resolved;
      }
    }

    // Stop at $HOME or filesystem root — never walk past either.
    final parent = current.parent;
    final atHome = current.absolute.path == Directory(home).absolute.path;
    final atRoot = parent.path == current.path;
    if (atHome || atRoot) break;
    current = parent;
  }

  // No live session found — keep _sessionDir at <CWD>/.fdb/ so commands like
  // `status` can handle the missing-session case themselves.
  _sessionDir = '$cwd/$sessionDirName';
  return null;
}