resolve method

@override Future<DatumConflictResolution<T>> resolve({ T? local, T? remote, required DatumConflictContext context, })

Resolves a conflict between a local and remote version of an entity.

Implementation

@override
Future<DatumConflictResolution<T>> resolve({
  T? local,
  T? remote,
  required DatumConflictContext context,
}) async {
  if (local == null && remote == null) {
    return DatumConflictResolution.abort(
      'No entities supplied to CRDT resolver.',
    );
  }

  // A deletion conflict has no second state to merge with — preserve the
  // content that still exists so the document cannot be lost, and let the
  // engine converge the other side.
  if (remote == null) {
    return DatumConflictResolution.useLocal(local as T);
  }
  if (local == null) {
    return DatumConflictResolution.useRemote(remote);
  }

  final merged = local.merge(remote) as T;

  // `DatumEntityMixin.merge` defaults to `=> other`. If the "merge" is
  // literally the remote instance while the two sides differ, the entity
  // almost certainly never implemented CRDT merging — surface it instead
  // of silently discarding the local edits.
  if (identical(merged, remote) && local != remote) {
    return DatumConflictResolution.merge(
      merged,
      message: 'Entity ${context.entityId} resolved with the DEFAULT merge (=> other): '
          'the entity type does not override merge(), so CRDTResolver degraded '
          'to take-remote and any concurrent local edits were discarded. '
          'Override merge() to combine CRDT fields.',
    );
  }

  return DatumConflictResolution.merge(merged);
}