Feature/nat 217 import sites

gso/api/api_v1/endpoints/import_site.py

 from typing import Dict, Any
 
-from fastapi import HTTPException
+from fastapi import HTTPException, status
 from fastapi.routing import APIRouter
-from orchestrator.services import processes
+from orchestrator.services import processes, subscriptions
 from pydantic import BaseModel
 
 from gso.products.product_blocks.site import SiteTier
@@ -20,19 +20,31 @@ class SiteImport(BaseModel):
     site_bgp_community_id: int
     site_internal_id: int
     site_tier: SiteTier
+    site_ts_address: str
 
 
-@router.post("/", tags=["Import"])
+@router.post("/", status_code=status.HTTP_201_CREATED, tags=["Import"])
 def import_site(site: SiteImport) -> Dict[str, Any]:
     """
     Import site by running the import_site workflow.
+    response:
+        - pid: The process id of the started process.
+    Raises:
+    HTTPException: If the site already exists or if there's an error in the process.
     """
+    subscription = subscriptions.retrieve_subscription_by_subscription_instance_value(
+        resource_type="site_name", value=site.site_name, sub_status=("provisioning", "active"))
+    if subscription:
+        raise HTTPException(status_code=status.HTTP_409_CONFLICT, detail="Site already exists.")
+
     pid = processes.start_process("import_site", [site.dict()])
     if pid is None:
-        raise HTTPException(status_code=500, detail="Failed to start the process.")
+        raise HTTPException(status_code=status.HTTP_500_INTERNAL_SERVER_ERROR, detail="Failed to start the process.")
 
     process = processes._get_process(pid)  # pylint: disable=protected-access
     if process.last_status == "failed":
         raise HTTPException(
-            status_code=500, detail=f"Process {pid} failed because of an internal error.")
+            status_code=status.HTTP_500_INTERNAL_SERVER_ERROR,
+            detail=f"Process {pid} failed because of an internal error.")
+
     return {"pid": str(pid)}