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('$base/api/packages/$package');
  final response = await _http.get(uri, headers: headers);
  if (response.statusCode != 200) {
    throw StateError(
      'pub: failed to fetch "$package": ${response.statusCode}',
    );
  }

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

  Version? best;
  String? bestStr;
  for (final v in versions) {
    final vStr = (v as Map<String, dynamic>)['version'] as String;
    final ver = Version.parse(vStr);
    if (vc.allows(ver) && (best == null || ver > best)) {
      best = ver;
      bestStr = vStr;
    }
  }
  if (bestStr == null) {
    throw StateError('pub: no version of "$package" matches "$constraint"');
  }
  return bestStr;
}