feat: email the new owner when their ownership transfer completes

app/mailers/school_ownership_mailer.rb

@@ -15,6 +15,16 @@ def request_ownership_transfer
          message_stream: 'outbound')
   end
 
+  def complete_ownership_transfer
+    @school = ownership_transfer.school
+    @new_owner_name = users_by_id[ownership_transfer.nominated_user_id]&.name.presence || 'there'
+
+    mail(to: ownership_transfer.email_address,
+         subject: "You're now the owner of the Code Classroom account for #{@school.name}",
+         track_opens: 'true',
+         message_stream: 'outbound')
+  end
+
   private
 
   def ownership_transfer

app/models/ownership_transfer.rb

@@ -19,6 +19,8 @@ class OwnershipTransfer < ApplicationRecord
   validate :nominee_has_the_school_teacher_role_for_the_school
 
   after_create_commit :send_ownership_transfer_request_email
+  after_update_commit :send_ownership_transfer_completed_email,
+                      if: -> { saved_change_to_status?(from: 'pending', to: 'completed') }
   encrypts :email_address
 
   private
@@ -35,4 +37,8 @@ def nominee_has_the_school_teacher_role_for_the_school
   def send_ownership_transfer_request_email
     SchoolOwnershipMailer.with(ownership_transfer: self).request_ownership_transfer.deliver_later
   end
+
+  def send_ownership_transfer_completed_email
+    SchoolOwnershipMailer.with(ownership_transfer: self).complete_ownership_transfer.deliver_later
+  end
 end

app/views/school_ownership_mailer/complete_ownership_transfer.text.erb

@@ -0,0 +1,16 @@
+Hi <%= @new_owner_name %>,
+
+Ownership of the Code Classroom account for <%= @school.name %> has been transferred to you.
+
+As the owner, you can now:
+
+- Manage school members: https://classroom.raspberrypi.org/en-US/school/members
+- Access school settings and feature controls: https://classroom.raspberrypi.org/en-US/school/settings
+- Invite a new teacher to the account
+- Transfer ownership to someone else if needed
+- Delete students
+
+To access more resources, please visit our Help Center: https://help.editor.raspberrypi.org/hc/en-us/categories/115000275003-Code-Editor-for-Education
+
+Kind Regards,
+The Code Classroom team

spec/mailers/previews/school_ownership_mailer_preview.rb

@@ -17,6 +17,19 @@ def request_ownership_transfer
     with_stubbed_user_info_api { SchoolOwnershipMailer.with(ownership_transfer:).request_ownership_transfer.message }
   end
 
+  def complete_ownership_transfer
+    school = School.new(name: 'Elmwood Secondary School')
+    ownership_transfer = OwnershipTransfer.new(
+      email_address: 'teacher@example.com',
+      school:,
+      nominated_user_id: NOMINEE[:id],
+      requested_by_user_id: REQUESTED_OWNER[:id],
+      status: :completed
+    )
+
+    with_stubbed_user_info_api { SchoolOwnershipMailer.with(ownership_transfer:).complete_ownership_transfer.message }
+  end
+
   private
 
   # fake the user info response, but only for the duration of

spec/mailers/school_ownership_mailer_spec.rb

@@ -41,4 +41,57 @@
       expect(email.subject).to include(ownership_transfer.school.name)
     end
   end
+
+  describe 'complete_ownership_transfer' do
+    subject(:email) { described_class.with(ownership_transfer:).complete_ownership_transfer }
+
+    let(:school) { create(:verified_school) }
+    let(:nominee) { create(:teacher, school:) }
+    let(:requested_owner) { create(:owner, school:) }
+    let(:ownership_transfer) do
+      create(
+        :ownership_transfer,
+        school:,
+        nominated_user_id: nominee.id,
+        requested_by_user_id: requested_owner.id,
+        status: :completed
+      )
+    end
+
+    before do
+      stub_user_info_api_fetch_by_ids(
+        user_ids: [nominee.id, requested_owner.id],
+        users: [{ id: nominee.id, name: nominee.name }, { id: requested_owner.id, name: requested_owner.name }]
+      )
+    end
+
+    it 'is sent to the new owner' do
+      expect(email.to).to eq([ownership_transfer.email_address])
+    end
+
+    it 'includes the new owner\'s name in the body' do
+      expect(email.body.to_s).to include(nominee.name)
+    end
+
+    it 'includes the school name in the body' do
+      expect(email.body.to_s).to include(ownership_transfer.school.name)
+    end
+
+    it 'includes the school name in the subject' do
+      expect(email.subject).to include(ownership_transfer.school.name)
+    end
+
+    context 'when the new owner is missing from the user-info response' do
+      before do
+        stub_user_info_api_fetch_by_ids(
+          user_ids: [nominee.id, requested_owner.id],
+          users: [{ id: requested_owner.id, name: requested_owner.name }]
+        )
+      end
+
+      it 'greets them generically instead of leaving the greeting blank' do
+        expect(email.body.to_s).to include('Hi there,')
+      end
+    end
+  end
 end

spec/models/ownership_transfer_spec.rb

@@ -173,4 +173,38 @@
       )
     end
   end
+
+  describe 'the completion email' do
+    before { ownership_transfer.save! }
+
+    it 'is enqueued with the transfer as the mailer param when the transfer completes' do
+      ownership_transfer.update!(status: :completed)
+
+      assert_enqueued_email_with(
+        SchoolOwnershipMailer, :complete_ownership_transfer, params: { ownership_transfer: }
+      )
+    end
+
+    it 'is not enqueued when the transfer resolves to a different status' do
+      assert_no_enqueued_emails do
+        ownership_transfer.update!(status: :rejected)
+      end
+    end
+
+    it 'is not enqueued when an already-completed transfer is saved again unchanged' do
+      ownership_transfer.update!(status: :completed)
+
+      assert_no_enqueued_emails do
+        ownership_transfer.update!(status: :completed)
+      end
+    end
+
+    it 'is not enqueued when a non-pending transfer is corrected to completed' do
+      ownership_transfer.update!(status: :rejected)
+
+      assert_no_enqueued_emails do
+        ownership_transfer.update!(status: :completed)
+      end
+    end
+  end
 end