public async Task <HistoryViewModel> Add(string key, HistoryViewModel viewModel, CancellationToken cancellationToken)
{
var record = viewModel.ToRecord();
record.Key = key;
record.Timestamp = DateTime.Now;
var last = await HistoryRepository.GetLast(key, cancellationToken);
if (last != null)
{
record.OldValue = last.NewValue;
}
await HistoryRepository.Add(record, cancellationToken);
return(record.ToViewModel());
}