Add hierarchical policy simulation helpers

src/govoplan_policy/backend/api/v1/routes.py

@@ -24,6 +24,7 @@ from govoplan_policy.backend.retention import (
     parent_privacy_policy,
     parent_privacy_policy_sources,
     set_privacy_policy_for_scope,
+    simulate_privacy_policy_change,
 )
 
 from .schemas import (
@@ -31,6 +32,7 @@ from .schemas import (
     PrivacyRetentionPolicyItem,
     PrivacyRetentionPolicyScopeRequest,
     PrivacyRetentionPolicyScopeResponse,
+    PrivacyRetentionPolicySimulationResponse,
     RetentionRunRequest,
     RetentionRunResponse,
 )
@@ -200,6 +202,32 @@ def explain_privacy_retention_policy(
         raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail=str(exc)) from exc
 
 
+@router.post("/privacy-retention/policies/{scope_type}/simulate", response_model=PrivacyRetentionPolicySimulationResponse)
+def simulate_privacy_retention_policy(
+    scope_type: str,
+    payload: PrivacyRetentionPolicyScopeRequest,
+    scope_id: str | None = Query(default=None),
+    session: Session = Depends(get_session),
+    principal: ApiPrincipal = Depends(get_api_principal),
+):
+    clean_scope = scope_type.strip().casefold()
+    _require_privacy_policy_write(principal, clean_scope)
+    try:
+        return PrivacyRetentionPolicySimulationResponse(
+            scope_type=clean_scope,
+            scope_id=scope_id,
+            simulation=simulate_privacy_policy_change(
+                session,
+                tenant_id=principal.tenant_id,
+                scope_type=clean_scope,
+                scope_id=scope_id,
+                policy=payload.policy.model_dump(mode="json", exclude_none=True),
+            ),
+        )
+    except PrivacyPolicyError as exc:
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail=str(exc)) from exc
+
+
 def _blocked_privacy_retention_fields(parent) -> list[str]:
     if parent is None:
         return []