♻️(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/services/marketing_service.py

@@ -0,0 +1,134 @@
+"""Marketing service in charge of pushing data for marketing automation."""
+
+import logging
+from dataclasses import dataclass
+from functools import lru_cache
+from typing import Dict, List, Optional, Protocol
+
+from django.conf import settings
+from django.core.exceptions import ImproperlyConfigured
+from django.utils.module_loading import import_string
+
+import brevo_python
+
+logger = logging.getLogger(__name__)
+
+
+class ContactCreationError(Exception):
+    """Raised when the contact creation fails."""
+
+
+@dataclass
+class ContactData:
+    """Contact data for marketing service integration."""
+
+    email: str
+    attributes: Optional[Dict[str, str]] = None
+    list_ids: Optional[List[int]] = None
+    update_enabled: bool = True
+
+
+class MarketingServiceProtocol(Protocol):
+    """Interface for marketing automation service integrations."""
+
+    def create_contact(
+        self, contact_data: ContactData, timeout: Optional[int] = None
+    ) -> dict:
+        """Create or update a contact.
+
+        Args:
+            contact_data: Contact information and attributes
+            timeout: API request timeout in seconds
+
+        Returns:
+            dict: Service response
+
+        Raises:
+            ContactCreationError: If contact creation fails
+        """
+
+
+class BrevoMarketingService:
+    """Brevo marketing automation integration.
+
+    Handles:
+    - Contact management and segmentation
+    - Marketing campaigns and automation
+    - Email communications
+
+    Configuration via Django settings:
+    - BREVO_API_KEY: API authentication
+    - BREVO_API_CONTACT_LIST_IDS: Default contact lists
+    - BREVO_API_CONTACT_ATTRIBUTES: Default contact attributes
+    """
+
+    def __init__(self):
+        """Initialize Brevo (ex-sendinblue) marketing service."""
+
+        if not settings.BREVO_API_KEY:
+            raise ImproperlyConfigured("Brevo API key is required")
+
+        configuration = brevo_python.Configuration()
+        configuration.api_key["api-key"] = settings.BREVO_API_KEY
+
+        self._api_client = brevo_python.ApiClient(configuration)
+
+    def create_contact(self, contact_data: ContactData, timeout=None) -> dict:
+        """Create or update a Brevo contact.
+
+        Args:
+            contact_data: Contact information and attributes
+            timeout: API request timeout in seconds
+
+        Returns:
+            dict: Brevo API response
+
+        Raises:
+            ContactCreationError: If contact creation fails
+            ImproperlyConfigured: If required settings are missing
+
+        Note:
+            Contact attributes must be pre-configured in Brevo.
+            Changes to attributes can impact existing workflows.
+        """
+
+        if not settings.BREVO_API_CONTACT_LIST_IDS:
+            raise ImproperlyConfigured(
+                "Default Brevo List IDs must be configured in settings."
+            )
+
+        contact_api = brevo_python.ContactsApi(self._api_client)
+
+        attributes = {
+            **settings.BREVO_API_CONTACT_ATTRIBUTES,
+            **(contact_data.attributes or {}),
+        }
+
+        list_ids = (contact_data.list_ids or []) + settings.BREVO_API_CONTACT_LIST_IDS
+
+        contact = brevo_python.CreateContact(
+            email=contact_data.email,
+            attributes=attributes,
+            list_ids=list_ids,
+            update_enabled=contact_data.update_enabled,
+        )
+
+        api_configurations = {}
+
+        if timeout is not None:
+            api_configurations["_request_timeout"] = timeout
+
+        try:
+            response = contact_api.create_contact(contact, **api_configurations)
+        except brevo_python.rest.ApiException as err:
+            logger.exception("Failed to create contact in Brevo")
+            raise ContactCreationError("Failed to create contact in Brevo") from err
+
+        return response
+
+
+@lru_cache(maxsize=1)
+def get_marketing_service() -> MarketingServiceProtocol:
+    """Return cached instance of configured marketing service."""
+    marketing_service_cls = import_string(settings.MARKETING_SERVICE_CLASS)
+    return marketing_service_cls()