#Scheduler
##Concept
The Scheduler service is used to give users the ability to create scheduled reminders. For example, a user of the BeuthBot might want to be informed of the canteen menu on a daily basis. For this he would send a message to the bot, asking it to send him the menu every morning at nine o clock.
If Rasa identifies this message as an attempt to create such a reminder, it will extract a createReminder-intent, along with entities for date, time, cycle and event.
##The reminder object
The date-entity contains the given day on which this reminder should be sent.
time contains the time at which the reminder should be sent.
cycle contains a value defining the interval at which the reminder should be sent. This can either be DAILY, WEEKLY,MONTHLY or ONCE for reminders that should only be sent on one specific date.
The `event-entity contains the object of which the user wishes to be reminded. Currently, only canteen-menu-reminders are supported, but this can expanded to any type of object (e.g. course-timetables), given the data-infrastructure.
##Scheduler class
The Scheduler-class is implemented as a singleton, using the @Singleton-annotation, along with a @Startup-annotation to make sure an instance of it is created during startup, without the need to be instantiated by another service.
###Creating reminders
A reminder is created via the createReminder-function, which requires a TaskMessage and AppUser as parameters. The TaskMessage-object is required to read out the entities mentioned above, which are used as parameters to create a new instance of a Reminder-object which is then stored in the reminders-array and inserted into the database.
The createReminder-function returns the created reminder object which can then be further used by the Drools-service to create a response for the user. Should errors occur along the way, the function returns null, giving Drools the opportunity to tell the user that creation of the reminder has failed. This functionality could be expanded to explain to the user what exactly went wrong.
###Sending reminders
To send users the reminders they have asked for, the Scheduler-class makes use of the EJB-annotation @Schedule, which is set to fire once every minute, searching the database for Reminder-objects whose date and time settings match the timestamp at which the function has fired, and if so, forwards this information to Drools, where the appropriate messages can be created and relayed to the users.
###Deleting reminders
If a user wishes to no longer be reminded of these events, he can ask the bot to stop sending him reminders, which will cause drools to fire the delete reminder rule, in turn causing the schedulerService to sift through all reminders associated with this user and removing them.