Expose 'reminder_at' to users and schedule

app/controllers/activities_controller.rb

 
     # Never trust parameters from the scary internet, only allow the white list through.
     def activity_params
-      params.require(:activity).permit(:name, :description, :location, :start, :end, :deadline)
+      params.require(:activity).permit(:name, :description, :location, :start, :end, :deadline, :reminder_at)
     end
 end

app/models/activity.rb

   validates :start, presence: true
   validate  :deadline_before_start, unless: "self.deadline.blank?"
   validate  :end_after_start,       unless: "self.end.blank?"
+  validate  :reminder_before_deadline, unless: "self.reminder_at.blank?"
 
   after_create :create_missing_participants!
+  after_commit :schedule_reminder, if: Proc.new {|a| a.previous_changes["reminder_at"] }
 
   # Get all people (not participants) that are organizers. Does not include
   # group leaders, although they may modify the activity as well.
 
     participants = self.participants.where(attending: nil)
     participants.each { |p| p.send_reminder }
+
+    self.reminder_done = true
+    self.save
+  end
+
+  def schedule_reminder
+    return if self.reminder_at.nil? || self.reminder_done
+
+    self.delay(run_at: self.reminder_at).send_reminder
   end
 
   private
       errors.add(:end, I18n.t('activities.errors.must_be_after_start'))
     end
   end
+
+  # Assert that the reminder for non-response is sent while participants still
+  # can change their response.
+  def reminder_before_deadline
+    if self.reminder_at > self.deadline
+      errors.add(:reminder_at, I18n.t('activities.errors.must_be_before_deadline'))
+    end
+  end
 end

app/models/participant.rb

     return unless self.attending.nil?
 
     self.attending = true
+    notes = self.notes || ""
+    notes << '[auto]'
+    self.notes = notes
     self.save
 
     ParticipantMailer.attendance_reminder(self.person, self.activity).deliver_later

app/views/activities/_form.html.erb

       <%= f.label :deadline %>
       <%= f.datetime_field :deadline, class: 'form-control' %>
     </div>
+    <div class="form-group">
+      <%= f.label :reminder_at %>
+      <%= f.datetime_field :reminder_at, class: 'form-control' %>
+    </div>
     <%= f.submit %>
   </div>
 <% end %>

app/views/api/activities/show.rabl

 object @activity
 
-attributes :id, :name, :start, :end, :deadline, :location
+attributes :id, :name, :start, :end, :deadline, :location, :reminder_at
 
 node :response_counts do
   c = @activity.state_counts

config/locales/activities/nl.yml

     errors:
       must_be_before_start: "moet voor start zijn"
       must_be_after_start: "moet na start zijn"
+      must_be_before_deadline: "moet voor deadline zijn"
       already_in: "persoon doet al mee aan activiteit"
 
     participant:

config/locales/translation_nl.yml

         participants: Deelnemers  #g
         people: Mensen  #g
         start: Start  #g
+        reminder_at: Herinnering om
+        reminder_done: Herinnering verstuurd
 
       group:
         activities: Activiteiten  #g