Add ParticipantMailer

app/mailers/participant_mailer.rb

+class ParticipantMailer < ApplicationMailer
+  def attendance_reminder(person, activity)
+    @person = person
+    @activity = activity
+
+    subject = I18n.t('activities.emails.attendance_reminder.subject', activity: @activity.name)
+
+    mail(to: @person.email, subject: subject)
+  end
+end

app/models/activity.rb

   #     when the normal participants (everyone who isn't an organizer or group
   #     leader) may not change their own attendance anymore. Disabled if set to
   #     nil.
+  #
+  # @!attribute reminder_at
+  #   @return [TimeWithZone]
+  #     when all participants which haven't responded yet (attending is nil)
+  #     will be automatically set to 'present' and emailed. Must be before the
+  #     deadline, disabled if nil.
+  #
+  # @!attribute reminder_done
+  #   @return [Boolean]
+  #     whether or not sending the reminder has finished.
 
   belongs_to :group
 
     result
   end
 
+  # Send a reminder to all participants who haven't responded, and set their
+  # response to 'attending'.
+  def send_reminder
+    # Sanity check that the reminder date didn't change while queued.
+    return unless !self.reminder_done && self.reminder_at
+    return if self.reminder_at > Time.zone.now
+
+    participants = self.participants.where(attending: nil)
+    participants.each { |p| p.send_reminder }
+  end
+
   private
   # Assert that the deadline for participants to change the deadline, if any,
   # is set before the event starts.

app/models/participant.rb

     self.activity.may_change?(person) ||
     self.person == person
   end
+
+  # Set attending to true if nil, and notify the Person via email.
+  def send_reminder
+    return unless self.attending.nil?
+
+    self.attending = true
+    self.save
+
+    ParticipantMailer.attendance_reminder(self.person, self.activity).deliver_later
+  end
+
 end

app/views/participant_mailer/attendance_reminder.html.haml

+%p= t 'authentication.emails.greeting', name: @person.first_name
+
+%p= t 'activities.emails.attendance_reminder.havenot_responded', activity: @activity.name
+
+%p= t 'activities.emails.attendance_reminder.if_cannot', deadline: l(@activity.deadline, format: :short)
+
+%p
+  = link_to group_activity_url(@activity.group, @activity) do
+    = t 'activities.emails.open_activity'
+
+%p
+  = t('activities.emails.ending').sample
+  %br
+  Aardbei
+
+%hr
+%footer
+  %p
+    = t 'activities.emails.dont_want_mail'
+    %a{href: "https://aardbei.maartenberg.nl/settings"}
+      = t 'activities.emails.open_settings'

app/views/participant_mailer/attendance_reminder.text.erb

+<%= t 'authentication.emails.greeting', name: @person.first_name %>
+
+<%= t 'activities.emails.attendance_reminder.havenot_responded', activity: @activity.name %>
+
+<%= t 'activities.emails.attendance_reminder.if_cannot', deadline: l(@activity.deadline, format: :short) %>
+
+<%= group_activity_url(@activity.group, @activity) %>
+
+<%= t('activities.emails.ending').sample %>
+Aardbei
+
+---
+<%= t 'activities.emails.dont_want_mail' %>
+https://aardbei.maartenberg.nl/settings

config/environments/development.rb

   # routes, locales, etc. This feature depends on the listen gem.
   config.file_watcher = ActiveSupport::EventedFileUpdateChecker
 
-  config.action_mailer.delivery_method = ENV['MAIL_METHOD']
+  config.action_mailer.delivery_method = ENV['MAIL_METHOD'].to_sym
   config.action_mailer.smtp_settings = {
     address: ENV['SMTP_SERVER'],
     user_name: ENV['SMTP_USER'],

config/environments/production.rb

   # Do not dump schema after migrations.
   config.active_record.dump_schema_after_migration = false
 
-  config.action_mailer.delivery_method = ENV['MAIL_METHOD']
+  config.action_mailer.delivery_method = ENV['MAIL_METHOD'].to_sym
   config.action_mailer.smtp_settings = {
     address: ENV['SMTP_SERVER'],
     user_name: ENV['SMTP_USER'],

config/locales/activities/en.yml

       organizers: "Organizers"
       description: "Description"
       deadline: "Deadline"
+
+    emails:
+      open_activity: "Open activity"
+      open_settings: "Preferences"
+      dont_want_mail: "If you no longer want to receive these emails, change your preferences using the following link:"
+      ending:
+        - "Cheers,"
+      attendance_reminder:
+        subject: "You are now listed as 'attending' for %{activity}"
+        havenot_responded: "You have not yet indicated if you will be at %{activity}. Because we assume that you're present if you don't respond, your response has been set to 'attending'."
+        if_cannot: "If you wish to change this, you can change your response until %{deadline} using the following link:"

config/locales/activities/nl.yml

       organizers: "Organisatoren"
       description: "Omschrijving"
       deadline: "Deadline"
+
+    emails:
+      open_activity: "Activiteit openen"
+      open_settings: "Instellingen"
+      dont_want_mail: "Als je dit soort mailtjes niet meer wilt ontvangen, kun je dit uitschakelen via de volgende link:"
+      ending:
+        - "Met griendelijke vroet,"
+        - "Met groetelijke doei,"
+        - "Hopende je voldoende te hebben geïnformeerd,"
+        - "Met aanmeldende groet,"
+        - "Met grappige tekst onderaan de mail,"
+        - "Met geautomatiseerde groet,"
+        - "Doi,"
+        - "Talla,"
+      attendance_reminder:
+        subject: "Je bent automatisch aangemeld voor %{activity}"
+        havenot_responded: "Je hebt nog niet aangegeven of je bij %{activity} kunt zijn. Omdat we ervan uitgaan dat je er bent als je niks aangeeft, is je reactie automatisch op 'aanwezig' gezet."
+        if_cannot: "Als je toch niet aanwezig kunt zijn, kan je dit tot %{deadline} aangeven via de volgende link:"

db/schema.rb

 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20170916212858) do
+ActiveRecord::Schema.define(version: 20170917093221) do
 
   create_table "activities", force: :cascade do |t|
     t.string   "name"
     t.datetime "end"
     t.datetime "deadline"
     t.integer  "group_id"
-    t.datetime "created_at",  null: false
-    t.datetime "updated_at",  null: false
+    t.datetime "created_at",    null: false
+    t.datetime "updated_at",    null: false
+    t.datetime "reminder_at"
+    t.boolean  "reminder_done"
     t.index ["group_id"], name: "index_activities_on_group_id"
   end