app/mailers/admin_mailer.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+class AdminMailer < ApplicationMailer
+  def attendance_change_email
+    @guest = Guest.find(params[:guest_id])
+
+    mail(
+      to: @guest.wedding.users.pluck(:email),
+      subject: I18n.t(
+        'admin_mailer.attendance_change_email.subject',
+        name: @guest.name,
+        status: I18n.t("active_record.attributes.guest/status.#{@guest.status}")
+      )
+    )
+  end
+end

app/models/wedding.rb

@@ -23,5 +23,6 @@ class Wedding < ApplicationRecord
   has_many :guests, dependent: :delete_all
   has_many :groups, dependent: :delete_all
   has_many :invitations, dependent: :delete_all
+  has_many :users, dependent: :delete_all
   has_one :website, dependent: :destroy
 end

app/views/admin_mailer/attendance_change_email.html.erb

@@ -0,0 +1,15 @@
+<p><%= I18n.t('admin_mailer.greeting') %>,</p>
+
+<p>
+  <%= I18n.t('admin_mailer.attendance_change_email.paragraph_1', name: @guest.name) %>
+</p>
+
+<ul>
+  <li>
+    <strong><%= I18n.t("active_record.attributes.guest.status") %>:</strong> <%= I18n.t("active_record.attributes.guest/status.#{@guest.status}") %>
+  </li>
+</ul>
+
+<p>
+  <%= I18n.t("admin_mailer.attendance_change_email.notify_on_updates") %>
+</p>

app/views/admin_mailer/attendance_change_email.text.erb

@@ -0,0 +1,7 @@
+<%= I18n.t('admin_mailer.greeting') %>,
+
+<%= I18n.t('admin_mailer.attendance_change_email.paragraph_1', name: @guest.name) %>
+
+- <%= I18n.t("active_record.attributes.guest.status") %>: <%= I18n.t("active_record.attributes.guest/status.#{@guest.status}") %>
+
+<%= I18n.t("admin_mailer.attendance_change_email.notify_on_updates") %>

config/locales/en.yml

@@ -1,31 +1,19 @@
-# Files in the config/locales directory are used for internationalization and
-# are automatically loaded by Rails. If you want to use locales other than
-# English, add the necessary files in this directory.
-#
-# To use the locales, use `I18n.t`:
-#
-#     I18n.t "hello"
-#
-# In views, this is aliased to just `t`:
-#
-#     <%= t("hello") %>
-#
-# To use a different locale, set it with `I18n.locale`:
-#
-#     I18n.locale = :es
-#
-# This would use the information in config/locales/es.yml.
-#
-# To learn more about the API, please read the Rails Internationalization guide
-# at https://guides.rubyonrails.org/i18n.html.
-#
-# Be aware that YAML interprets the following case-insensitive strings as
-# booleans: `true`, `false`, `on`, `off`, `yes`, `no`. Therefore, these strings
-# must be quoted to be interpreted as strings. For example:
-#
-#     en:
-#       "yes": yup
-#       enabled: "ON"
-
 en:
   hello: "Hello world"
+  active_record:
+    attributes:
+      guest:
+        status: Status
+      guest/status:
+        considered: Considered
+        invited: Invited
+        confirmed: Confirmed
+        declined: Declined
+        tentative: Tentative
+
+  admin_mailer:
+    greeting: "Dear user"
+    attendance_change_email:
+      subject: "%{name} has changed their attendance status: %{status}"
+      paragraph_1: "The guest %{name} has changed their attendance for the wedding."
+      notify_on_updates: "You will be notified of any further changes to their attendance status."