veilidchat/lib/chat/cubits/reconciliation/author_input_source.dart

import 'dart:math';

import 'package:async_tools/async_tools.dart';
import 'package:fast_immutable_collections/fast_immutable_collections.dart';
import 'package:meta/meta.dart';
import 'package:veilid_support/veilid_support.dart';

import '../../../proto/proto.dart' as proto;

@immutable
class InputWindow {
  const InputWindow({required this.elements, required this.firstPosition})
      : lastPosition = firstPosition + elements.length - 1,
        isEmpty = elements.length == 0,
        length = elements.length;

  final IList<OnlineElementState<proto.Message>> elements;
  final int firstPosition;
  final int lastPosition;
  final bool isEmpty;
  final int length;
}

class AuthorInputSource {
  AuthorInputSource.fromDHTLog(DHTLog dhtLog) : _dhtLog = dhtLog;

  ////////////////////////////////////////////////////////////////////////////

  Future<int> getTailPosition() =>
      _dhtLog.operate((reader) async => reader.length);

  Future<AsyncValue<InputWindow?>> getWindow(
          int startPosition, int windowLength) =>
      _dhtLog.operate((reader) async {
        // Don't allow negative length
        if (windowLength <= 0) {
          return const AsyncValue.data(null);
        }
        // Trim if we're beyond input source
        var endPosition = startPosition + windowLength - 1;
        startPosition = max(startPosition, 0);
        endPosition = max(endPosition, 0);

        // Get another input batch futher back
        try {
          Set<int>? offlinePositions;
          if (_dhtLog.writer != null) {
            offlinePositions = await reader.getOfflinePositions();
          }

          final messages = await reader.getRangeProtobuf(
              proto.Message.fromBuffer, startPosition,
              length: endPosition - startPosition + 1);
          if (messages == null) {
            return const AsyncValue.loading();
          }

          final elements = messages.indexed
              .map((x) => OnlineElementState(
                  value: x.$2,
                  isOffline: offlinePositions?.contains(x.$1 + startPosition) ??
                      false))
              .toIList();

          final window =
              InputWindow(elements: elements, firstPosition: startPosition);

          return AsyncValue.data(window);
        } on Exception catch (e, st) {
          return AsyncValue.error(e, st);
        }
      });

  ////////////////////////////////////////////////////////////////////////////
  final DHTLog _dhtLog;
}