Scheduling reminders

[jbockle]

When I was setting up some reminders I asked myself "how could I specify a specific time of day for the reminder to tick"? Its actually quite simple! Just set the dueTime to a specific time of day, or the next day if it has already passed.

// I want the reminder to run daily at 8pm
public async Task SetupReminder()
{
    const string reminderName = "foo";

    var firstTick = DateTime.Today.AddHours(20).ToUniversalTime(); // start the reminder at 8pm EST
    if (firstTick < DateTime.UtcNow)
    {
        // if the next start time has already passed, increase the startTime by a day
        firstTick = firstTick.AddDays(1);
    }

    var nextFirstTick = firstTick - DateTime.UtcNow; // aka dueTime
    var interval = TimeSpan.FromDays(1); // aka period

    await RegisterOrUpdateReminder(reminderName, nextFirstTick, interval);
}

One note, when implementing IRemindable.ReceiveReminder, if the reminder operation is long running, the reminder's period will only start after the operation has completed, causing the reminder period to shift after each reminder. To prevent that, discard the operation's task so it will continue in the background.

public Task ReceiverReminder(string reminderName, TickStatus status)
{
    _ = StartLongRunningOperation();
    return Task.CompletedTask;
}

public Task StartLongRunningOperation()
{
    return Task.Delay(TimeSpan.FromHours(1));
}