✨(backend) add email notifications for screen recordings

Implement backend method to send email notifications when screen recordings
are ready for download. Enables users to be alerted when their recordings are
available. Frontend implementation to follow in upcoming commits.

This service is triggered by the storage hook from Minio.

Add minimal unit test coverage for notification service, addressing previous
lack of tests in this area. The notification service was responsible for
calling the unstable summary service feature, which was developped way too
quickly.

The email template has been reviewed by a LLM, to make it user-friendly and
crystal clear.

src/backend/core/tests/recording/event/test_notification.py

@@ -0,0 +1,167 @@
+"""
+Test event notification.
+"""
+
+# pylint: disable=E1128,W0621,W0613,W0212
+
+import smtplib
+from unittest import mock
+
+from django.contrib.sites.models import Site
+
+import pytest
+
+from core import factories, models
+from core.recording.event.notification import NotificationService, notification_service
+
+pytestmark = pytest.mark.django_db
+
+
+@pytest.fixture
+def mocked_current_site():
+    """Mocks the Site.objects.get_current()to return a controlled predefined domain."""
+
+    site_mock = mock.Mock()
+    site_mock.domain = "test-domain.com"
+
+    with mock.patch.object(
+        Site.objects, "get_current", return_value=site_mock
+    ) as patched:
+        yield patched
+
+
+@mock.patch.object(NotificationService, "_notify_summary_service", return_value=True)
+def test_notify_external_services_transcript_mode(mock_notify_summary):
+    """Test notification routing for transcript mode recordings."""
+
+    service = NotificationService()
+
+    recording = factories.RecordingFactory(mode=models.RecordingModeChoices.TRANSCRIPT)
+    result = service.notify_external_services(recording)
+
+    assert result is True
+    mock_notify_summary.assert_called_once_with(recording)
+
+
+@mock.patch.object(NotificationService, "_notify_user_by_email", return_value=True)
+def test_notify_external_services_screen_recording_mode(mock_notify_email):
+    """Test notification routing for screen recording mode."""
+
+    service = NotificationService()
+
+    recording = factories.RecordingFactory(
+        mode=models.RecordingModeChoices.SCREEN_RECORDING
+    )
+
+    result = service.notify_external_services(recording)
+
+    assert result is True
+    mock_notify_email.assert_called_once_with(recording)
+
+
+def test_notify_external_services_unknown_mode(caplog):
+    """Test notification for unknown recording mode."""
+    recording = factories.RecordingFactory()
+
+    # Bypass validation
+    recording.mode = "unknown"
+
+    service = NotificationService()
+
+    result = service.notify_external_services(recording)
+
+    assert result is False
+    assert f"Unknown recording mode unknown for recording {recording.id}" in caplog.text
+
+
+def test_notify_user_by_email_success(mocked_current_site, settings):
+    """Test successful email notification to recording owners."""
+    settings.EMAIL_BRAND_NAME = "ACME"
+    settings.EMAIL_SUPPORT_EMAIL = "support@acme.com"
+    settings.EMAIL_LOGO_IMG = "https://acme.com/logo"
+    settings.SCREEN_RECORDING_BASE_URL = "https://acme.com/recordings"
+    settings.EMAIL_FROM = "notifications@acme.com"
+
+    recording = factories.RecordingFactory(room__name="Conference Room A")
+
+    owners = [
+        factories.UserRecordingAccessFactory(
+            recording=recording, role=models.RoleChoices.OWNER
+        ).user,
+        factories.UserRecordingAccessFactory(
+            recording=recording, role=models.RoleChoices.OWNER
+        ).user,
+    ]
+    owner_emails = [owner.email for owner in owners]
+
+    # Create non-owner users to verify they don't receive emails
+    factories.UserRecordingAccessFactory(
+        recording=recording, role=models.RoleChoices.MEMBER
+    )
+    factories.UserRecordingAccessFactory(
+        recording=recording, role=models.RoleChoices.ADMIN
+    )
+
+    notification_service = NotificationService()
+
+    with mock.patch("core.recording.event.notification.send_mail") as mock_send_mail:
+        result = notification_service._notify_user_by_email(recording)
+
+        assert result is True
+        mock_send_mail.assert_called_once()
+
+        subject, body, sender, recipients = mock_send_mail.call_args[0]
+
+        assert subject == "Your recording is ready"
+
+        # Verify email contains expected content
+        required_content = [
+            "ACME",  # Brand name
+            "support@acme.com",  # Support email
+            "https://acme.com/logo",  # Logo URL
+            f"https://acme.com/recordings/{recording.id}",  # Recording link
+            "Conference Room A",  # Room name
+            recording.created_at.strftime("%A %d %B %Y"),  # Formatted date
+            recording.created_at.strftime("%H:%M"),  # Formatted time
+        ]
+
+        for content in required_content:
+            assert content in body
+
+        assert sender == "notifications@acme.com"
+
+        # Verify all owners received the email (order-independent comparison)
+        assert sorted(recipients) == sorted(owner_emails)
+
+
+def test_notify_user_by_email_no_owners(mocked_current_site, caplog):
+    """Test email notification when no owners are found."""
+
+    # Recording with no access
+    recording = factories.RecordingFactory()
+
+    result = notification_service._notify_user_by_email(recording)
+
+    assert result is False
+    assert f"No owner found for recording {recording.id}" in caplog.text
+
+
+def test_notify_user_by_email_smtp_exception(mocked_current_site, caplog):
+    """Test email notification when an exception occurs."""
+
+    recording = factories.RecordingFactory(room__name="Conference Room A")
+    owner = factories.UserRecordingAccessFactory(
+        recording=recording, role=models.RoleChoices.OWNER
+    ).user
+
+    notification_service = NotificationService()
+
+    with mock.patch(
+        "core.recording.event.notification.send_mail",
+        side_effect=smtplib.SMTPException("SMTP Error"),
+    ) as mock_send_mail:
+        result = notification_service._notify_user_by_email(recording)
+
+        assert result is False
+        mock_send_mail.assert_called_once()
+        assert f"notification to ['{owner.email}'] was not sent" in caplog.text