import 'dart:convert';

/// Minimal reader retained only for endpoints that do not have an
/// authoritative generated protobuf model yet.
class ProtobufWireMessage {
  ProtobufWireMessage(this.bytes);

  final List<int> bytes;
  Map<int, List<Object>>? _cache;

  Map<int, List<Object>> get _fields => _cache ??= _read();
  int integer(int tag) => (_fields[tag]?.lastOrNull as int?) ?? 0;

  String string(int tag) {
    final value = _fields[tag]?.lastOrNull;
    return value is List<int> ? utf8.decode(value, allowMalformed: true) : '';
  }

  Map<int, List<Object>> _read() {
    final result = <int, List<Object>>{};
    var index = 0;

    int varint() {
      var value = 0;
      var shift = 0;
      while (index < bytes.length) {
        final byte = bytes[index++];
        value |= (byte & 127) << shift;
        if (byte < 128) return value;
        shift += 7;
      }
      throw const FormatException('Invalid protobuf');
    }

    while (index < bytes.length) {
      final key = varint();
      final tag = key >> 3;
      final Object field;
      if ((key & 7) == 0) {
        field = varint();
      } else if ((key & 7) == 2) {
        final length = varint();
        final end = index + length;
        if (end > bytes.length) throw const FormatException('Invalid protobuf');
        field = bytes.sublist(index, end);
        index = end;
      } else {
        throw const FormatException('Unsupported protobuf');
      }
      (result[tag] ??= []).add(field);
    }
    return result;
  }
}

extension on List<Object> {
  Object? get lastOrNull => isEmpty ? null : last;
}