♻️(backend) add MarketingService protocol and Brevo implementation

Introduced a MarketingService protocol for typed marketing operations,
allowing easy integration of alternative services.

Implemented a Brevo wrapper following the protocol to decouple
the codebase from the sdk. These implementations are simple and pragmatic.
Feel free to refactor them.

src/backend/core/tests/services/test_marketing_service.py

@@ -0,0 +1,187 @@
+"""
+Test marketing services.
+"""
+
+# pylint: disable=W0621,W0613
+
+from unittest import mock
+
+from django.conf import settings
+from django.core.exceptions import ImproperlyConfigured
+
+import brevo_python
+import pytest
+
+from core.services.marketing_service import (
+    BrevoMarketingService,
+    ContactCreationError,
+    ContactData,
+    get_marketing_service,
+)
+
+
+def test_init_missing_api_key(settings):
+    """Test initialization with missing API key."""
+    settings.BREVO_API_KEY = None
+    with pytest.raises(ImproperlyConfigured, match="Brevo API key is required"):
+        BrevoMarketingService()
+
+
+def test_create_contact_missing_list_ids(settings):
+    """Test contact creation with missing list IDs."""
+
+    settings.BREVO_API_KEY = "test-api-key"
+    settings.BREVO_API_CONTACT_LIST_IDS = None
+    settings.BREVO_API_CONTACT_ATTRIBUTES = {"source": "test"}
+
+    valid_contact_data = ContactData(
+        email="test@example.com",
+        attributes={"first_name": "Test"},
+        list_ids=[1, 2],
+        update_enabled=True,
+    )
+
+    brevo_service = BrevoMarketingService()
+
+    with pytest.raises(
+        ImproperlyConfigured, match="Default Brevo List IDs must be configured"
+    ):
+        brevo_service.create_contact(valid_contact_data)
+
+
+@mock.patch("brevo_python.ContactsApi")
+def test_create_contact_success(mock_contact_api):
+    """Test successful contact creation."""
+
+    mock_api = mock_contact_api.return_value
+
+    settings.BREVO_API_KEY = "test-api-key"
+    settings.BREVO_API_CONTACT_LIST_IDS = [1, 2, 3, 4]
+    settings.BREVO_API_CONTACT_ATTRIBUTES = {"source": "test"}
+
+    valid_contact_data = ContactData(
+        email="test@example.com",
+        attributes={"first_name": "Test"},
+        list_ids=[1, 2],
+        update_enabled=True,
+    )
+
+    brevo_service = BrevoMarketingService()
+
+    mock_api.create_contact.return_value = {"id": "test-id"}
+    response = brevo_service.create_contact(valid_contact_data)
+
+    assert response == {"id": "test-id"}
+
+    mock_api.create_contact.assert_called_once()
+    contact_arg = mock_api.create_contact.call_args[0][0]
+    assert contact_arg.email == "test@example.com"
+    assert contact_arg.attributes == {
+        **settings.BREVO_API_CONTACT_ATTRIBUTES,
+        **valid_contact_data.attributes,
+    }
+    assert set(contact_arg.list_ids) == {1, 2, 3, 4}
+    assert contact_arg.update_enabled is True
+
+
+@mock.patch("brevo_python.ContactsApi")
+def test_create_contact_with_timeout(mock_contact_api):
+    """Test contact creation with timeout."""
+
+    mock_api = mock_contact_api.return_value
+
+    settings.BREVO_API_KEY = "test-api-key"
+    settings.BREVO_API_CONTACT_LIST_IDS = [1, 2, 3, 4]
+    settings.BREVO_API_CONTACT_ATTRIBUTES = {"source": "test"}
+
+    valid_contact_data = ContactData(
+        email="test@example.com",
+        attributes={"first_name": "Test"},
+        list_ids=[1, 2],
+        update_enabled=True,
+    )
+
+    brevo_service = BrevoMarketingService()
+    brevo_service.create_contact(valid_contact_data, timeout=30)
+
+    mock_api.create_contact.assert_called_once()
+    assert mock_api.create_contact.call_args[1]["_request_timeout"] == 30
+
+
+@mock.patch("brevo_python.ContactsApi")
+def test_create_contact_api_error(mock_contact_api):
+    """Test contact creation API error handling."""
+
+    mock_api = mock_contact_api.return_value
+
+    settings.BREVO_API_KEY = "test-api-key"
+    settings.BREVO_API_CONTACT_LIST_IDS = [1, 2, 3, 4]
+    settings.BREVO_API_CONTACT_ATTRIBUTES = {"source": "test"}
+
+    valid_contact_data = ContactData(
+        email="test@example.com",
+        attributes={"first_name": "Test"},
+        list_ids=[1, 2],
+        update_enabled=True,
+    )
+
+    brevo_service = BrevoMarketingService()
+
+    mock_api.create_contact.side_effect = brevo_python.rest.ApiException()
+
+    with pytest.raises(ContactCreationError, match="Failed to create contact in Brevo"):
+        brevo_service.create_contact(valid_contact_data)
+
+
+@pytest.fixture
+def clear_marketing_cache():
+    """Clear marketing service cache between tests."""
+    get_marketing_service.cache_clear()
+    yield
+    get_marketing_service.cache_clear()
+
+
+def test_get_marketing_service_caching(clear_marketing_cache):
+    """Test marketing service caching behavior."""
+    settings.BREVO_API_KEY = "test-api-key"
+    settings.MARKETING_SERVICE_CLASS = (
+        "core.services.marketing_service.BrevoMarketingService"
+    )
+
+    service1 = get_marketing_service()
+    service2 = get_marketing_service()
+
+    assert service1 is service2
+    assert isinstance(service1, BrevoMarketingService)
+
+
+def test_get_marketing_service_invalid_class(clear_marketing_cache):
+    """Test handling of invalid service class."""
+    settings.MARKETING_SERVICE_CLASS = "invalid.service.path"
+
+    with pytest.raises(ImportError):
+        get_marketing_service()
+
+
+@mock.patch("core.services.marketing_service.import_string")
+def test_service_instantiation_called_once(mock_import_string, clear_marketing_cache):
+    """Test service class is instantiated only once."""
+
+    settings.BREVO_API_KEY = "test-api-key"
+    settings.MARKETING_SERVICE_CLASS = (
+        "core.services.marketing_service.BrevoMarketingService"
+    )
+    get_marketing_service.cache_clear()
+
+    mock_service_cls = mock.Mock()
+    mock_service_instance = mock.Mock()
+    mock_service_cls.return_value = mock_service_instance
+    mock_import_string.return_value = mock_service_cls
+
+    service1 = get_marketing_service()
+    service2 = get_marketing_service()
+
+    mock_import_string.assert_called_once_with(settings.MARKETING_SERVICE_CLASS)
+    mock_service_cls.assert_called_once()
+    assert service1 is service2
+    assert service1 is mock_service_instance