async public Task <IActionResult> Post()
{
var now = DateTimeOffset.UtcNow;
var subscriptions = await _subscriptionRepo.GetAll();
var users = await _userRepo.GetUsersWhoCanBeNotified(now);
var subscriptionsForUsers = subscriptions
.Join(users, s => s.UserId, u => u.Id, (s, u) => (u, s))
.Where(joined => !joined.Item2.UpdatedToday(joined.Item1, now))
.Select(joined => joined.Item2);
var snowfall = await _snowfallChecker.Check(subscriptionsForUsers);
var notifyTasks = snowfall.Select(s => notify(s.UserId, s.Subscriptions));
var saveTasks = snowfall
.SelectMany(s => _subscriptionRepo.CreateSaveTasks(s.Subscriptions));
await Task.WhenAll(notifyTasks.Concat(saveTasks));
return(Ok());
}