resolveVersion method

Implementation

@override
Future<String> resolveVersion(
  String package,
  String constraint, {
  String? registryUrl,
  Map<String, String>? headers,
}) async {
  final base = registryUrl ?? defaultUrl;
  final uri = Uri.parse('$base/$package');
  final reqHeaders = {'Accept': 'application/json', ...?headers};
  final response = await _http.get(uri, headers: reqHeaders);
  if (response.statusCode != 200) {
    throw StateError(
      'npm: failed to fetch "$package": ${response.statusCode}',
    );
  }

  final data = jsonDecode(response.body) as Map<String, dynamic>;
  final versions = data['versions'] as Map<String, dynamic>? ?? {};
  final vc = VersionConstraint.parse(constraint.isEmpty ? 'any' : constraint);

  Version? best;
  String? bestStr;
  for (final vStr in versions.keys) {
    try {
      final ver = Version.parse(vStr);
      if (vc.allows(ver) && (best == null || ver > best)) {
        best = ver;
        bestStr = vStr;
      }
    } catch (_) {
      // Skip invalid semver versions.
    }
  }
  if (bestStr == null) {
    throw StateError('npm: no version of "$package" matches "$constraint"');
  }
  return bestStr;
}