Reminder emails from Rails with SideKiq

Pre-text

Imagine you have an Rails app, that already uses SideKiq to queue the sending of emails. You need to add to this app and create a Rails model to represent a room booking.

At different stages of the booking you should do different things.

• When a booking is in ‘provisioned’, send a email to warning the room owner

• When a booking is ‘confirmed’, informed the booker their booking is confirmed.

• A booking can be altered before it becomes ‘live’

• 2 hours before the start time of the booking send the booker a reminder email.

Ruby

To help with th different states of a RoomBooking I have implemented the workflow gem, so workflow for RoomBooking, might look like:

workflow do
  state :draft do
    event :provision, :transitions_to => :provisional
  end
  state :provisional do
    event :confirm, :transitions_to => :confirmed
    on_entry do
      RoomBookingMailer.delay.inform_owner_of_booking(self.id)
    end
  end
  state :confirmed do
    event :activate, :transitions_to => :active
    on_entry do
      RoomBookingMailer.delay.inform_booker_of_booking_confirmation(self.id)
    end
  end
  state :active do
    event :complete, :transitions_to => :complete
  end
  state :complete do
  end
end

My Problem

What about the reminder??

I could schedule a task that checks upcoming bookings and sends out reminders when required. The thing I do not like about this is:

• I need to record I have sent out the reminder

• Process is defined outside of the RoomBooking

I could do:

RoomBookingMailer.delay_until( booking.start - 2.hours ).remind_booker_of_booking(self.id)

But what if they change their mind and alter the booking start time or cancel it, I would have to un-queue the reminder email and possibly queue another (messy!)

So I did this:

RoomBookingReminderWorker.perform_in(2.minutes, self.id, :customer_confirmed)

Then in that worker will (in 2 minutes) do the following:

• Checks to see if the booking is still valid

• Checks to see if it is time to send the reminder

If the booking it still valid and it is NOT time to send the reminder, it will simply schedule itself to run again in X amount of time.