Akka.Cluster.Reachability.Change C# (CSharp) Method

        private Reachability Change(UniqueAddress observer, UniqueAddress subject, ReachabilityStatus status)
        {
            var v = NextVersion(observer);
            var newVersions = _versions.SetItem(observer, v);
            var newRecord = new Record(observer, subject, status, v);
            var oldObserverRows = ObserverRows(observer);
            if (oldObserverRows == null && status == ReachabilityStatus.Reachable) return this;
            if (oldObserverRows == null) return new Reachability(_records.Add(newRecord), newVersions);

            Record oldRecord = null;
            oldObserverRows.TryGetValue(subject, out oldRecord);
            if (oldRecord == null)
            {
                if (status == ReachabilityStatus.Reachable &&
                    oldObserverRows.Values.All(r => r.Status == ReachabilityStatus.Reachable))
                {
                    return new Reachability(_records.FindAll(r => !r.Observer.Equals(observer)), newVersions);
                }
                return new Reachability(_records.Add(newRecord), newVersions);
            }
            if (oldRecord.Status == ReachabilityStatus.Terminated || oldRecord.Status == status)
                return this;

            if(status == ReachabilityStatus.Reachable && 
                oldObserverRows.Values.All(r => r.Status == ReachabilityStatus.Reachable || r.Subject.Equals(subject)))
                return new Reachability(_records.FindAll(r => !r.Observer.Equals(observer)), newVersions);

            var newRecords = _records.SetItem(_records.IndexOf(oldRecord), newRecord);
            return new Reachability(newRecords, newVersions);
        }