feat: add ImportService protocol and registry for OCP-compliant import extensibility (LP-7)

backend/app/domain/ports/import_service.py

@@ -0,0 +1,88 @@
+"""Port defining the common interface for data import services.
+
+All import services (Atomic Red Team, Sigma, CALDERA, etc.) follow the
+same contract: they receive a database session and return a summary dict
+with import statistics.
+
+New import sources can be added by:
+1. Implementing the ``ImportService`` protocol in a new module
+2. Registering the handler in the ``IMPORT_REGISTRY``
+
+This satisfies the Open/Closed Principle — the system is open for new
+import sources without modifying existing code.
+"""
+
+from __future__ import annotations
+
+from typing import Any, Protocol, runtime_checkable
+
+from sqlalchemy.orm import Session
+
+
+@runtime_checkable
+class ImportService(Protocol):
+    """Contract for any data-import operation.
+
+    Each implementation is a callable ``(Session) -> dict`` that
+    downloads, parses, and upserts records from an external source.
+    """
+
+    def __call__(self, db: Session) -> dict[str, Any]: ...
+
+
+class ImportServiceEntry:
+    """Lazy-loading wrapper that resolves a module-level function on first call."""
+
+    __slots__ = ("_module_path", "_func_name", "_resolved")
+
+    def __init__(self, module_path: str, func_name: str) -> None:
+        self._module_path = module_path
+        self._func_name = func_name
+        self._resolved: ImportService | None = None
+
+    def __call__(self, db: Session) -> dict[str, Any]:
+        if self._resolved is None:
+            import importlib
+            mod = importlib.import_module(self._module_path)
+            self._resolved = getattr(mod, self._func_name)
+        return self._resolved(db)
+
+    @property
+    def source_info(self) -> str:
+        return f"{self._module_path}.{self._func_name}"
+
+
+IMPORT_REGISTRY: dict[str, ImportServiceEntry] = {
+    "atomic_red_team": ImportServiceEntry(
+        "app.services.atomic_import_service", "import_atomic_red_team",
+    ),
+    "sigma": ImportServiceEntry(
+        "app.services.sigma_import_service", "sync",
+    ),
+    "lolbas": ImportServiceEntry(
+        "app.services.lolbas_import_service", "sync",
+    ),
+    "gtfobins": ImportServiceEntry(
+        "app.services.lolbas_import_service", "sync_gtfobins",
+    ),
+    "caldera": ImportServiceEntry(
+        "app.services.caldera_import_service", "sync",
+    ),
+    "elastic_rules": ImportServiceEntry(
+        "app.services.elastic_import_service", "sync",
+    ),
+    "mitre_cti": ImportServiceEntry(
+        "app.services.threat_actor_import_service", "sync",
+    ),
+    "d3fend": ImportServiceEntry(
+        "app.services.d3fend_import_service", "sync",
+    ),
+}
+
+
+def get_import_handler(source_name: str) -> ImportServiceEntry | None:
+    """Look up the import handler for *source_name*.
+
+    Returns ``None`` when no handler is registered.
+    """
+    return IMPORT_REGISTRY.get(source_name)