private static async Task <(bool, BackgroundTask)> QueueForExecutionAsync(this BackgroundTaskHost host,
Type type, object userData, Action <BackgroundTask> options)
{
var task = NewTask(host.Options, host.Serializer, type, userData);
options?.Invoke(task); // <-- at this stage, task should have a RunAt set by the user or it will be default
if (!string.IsNullOrWhiteSpace(task.Expression) && !task.HasValidExpression)
{
throw new ArgumentException("The provided CRON expression is invalid.");
}
// Handle when no start time is provided up front
if (task.RunAt == default)
{
task.RunAt = host.Store.GetTaskTimestamp();
if (task.NextOccurrence.HasValue)
{
task.RunAt = task.NextOccurrence.Value;
}
}
// Set the "Start" property only once, equal to the very first RunAt
task.Start = task.RunAt;
if (host.Store != null)
{
await host.Store.SaveAsync(task);
}
if (!host.Options.DelayTasks)
{
return(await host.AttemptTaskAsync(task, false), task);
}
return(true, task);
}
/// <summary>
/// Schedules a new task for delayed execution for the given host.
/// If the user does NOT provide a RunAt during options, but an expression IS provided, the next occurrence of the
/// expression, relative to now, will be selected as the start time.
/// Otherwise, the task will be scheduled for now.
/// </summary>
/// <param name="host"></param>
/// <param name="type"></param>
/// <param name="userData"></param>
/// <param name="options">
/// Allows configuring task-specific features. Note that this is NOT invoked at invocation time
/// lazily, but at scheduling time (i.e. immediately).
/// </param>
/// <returns>
/// Whether the scheduled operation was successful; if `true`, it was either scheduled or ran successfully,
/// depending on configuration. If `false`, it either failed to schedule or failed during execution, depending on
/// configuration.
/// </returns>
public static Task <(bool, BackgroundTask)> TryScheduleTaskAsync(this BackgroundTaskHost host, Type type,
object userData = null, Action <BackgroundTask> options = null)
{
return(host.QueueForExecutionAsync(type, userData, options));
}