C# DelayTimer

ITimerDataSource.cs

 public interface ITimerDataSource
{
    TimerTask LastTask();
    void RemoveTask(string taskid);
    void Insert(TimerTask task);
}

TimerTask.cs

 public class TimerTask
{
    public string TaskId { get; set; }
    public long TriggerTime { get; set; }
    public string EventName { get; set; }
    public string Argements { get; set; }
    public bool AllowDelayed { get; set; } = true;
}

TimerTrigger.cs

 public class TimerTrigger
{
    private ITimerDataSource _db { get; set; }
    private CancellationTokenSource _cancelSource { get; set; }
    private Task _task { get; set; }
    private Action<string, string> callback { get; set; }
    private volatile int _lock = 0;
    public int AllowDelaySeconds { get; set; } = 5;

    public TimerTrigger(ITimerDataSource db)
    {
        this._db = db;
    }
    private void WaitTask()
    {
        if(0 == Interlocked.Exchange(ref _lock, 1)) { 
            if (_task?.Status == TaskStatus.Running)
            {
                return;
            }
            _cancelSource = new CancellationTokenSource();
            _task = Task.Run(async () =>
            {
                var t = _db.LastTask();
                var n = DateTime.Now;
                if (t == null) return;
                if (t.TriggerTime > n.Ticks)
                {
                    var delay = new TimeSpan(t.TriggerTime - n.Ticks);
                    await Task.Delay(delay);
                }
                _db.RemoveTask(t.TaskId);
                new Task(() => DispatchTask(t)).Start();
            }, _cancelSource.Token);
            Interlocked.Exchange(ref _lock, 0);
        }
    }
    private void DispatchTask(TimerTask task)
    {
        WaitTask();
        if (task.TriggerTime < DateTime.Now.AddSeconds(-AllowDelaySeconds).Ticks)
        {
            if (!task.AllowDelayed)
            {
                return;
            }
        }
        callback?.Invoke(task.EventName, task.Argements);
    }
    public void Register(Action<string, string> action)
    {
        callback = action;
    }
    public void Start()
    {
        WaitTask();
    }
    public void InsertTask(TimerTask task)
    {
        if(task.TriggerTime < DateTime.Now.AddSeconds(AllowDelaySeconds).Ticks)
        {
            if (task.AllowDelayed)
            {
                callback?.Invoke(task.EventName, task.Argements);
                return;
            }
        }

        _db.Insert(task);
        _cancelSource?.Cancel();
        WaitTask();
    }
}