feature(backups): deny adding a backup job if another one is already queued

selfprivacy_api/backup/jobs.py

@@ -1,14 +1,39 @@
-from typing import Optional
+from typing import Optional, List
 
 from selfprivacy_api.jobs import Jobs, Job, JobStatus
 from selfprivacy_api.services.service import Service
 
 
-def backup_job_type(service: Service):
+def job_type_prefix(service: Service) -> str:
-    return f"services.{service.get_id()}.backup"
+    return f"services.{service.get_id()}"
+
+
+def backup_job_type(service: Service) -> str:
+    return f"{job_type_prefix(service)}.backup"
+
+
+def get_jobs_by_service(service: Service) -> List[Job]:
+    result = []
+    for job in Jobs.get_jobs():
+        if job.type_id.startswith(job_type_prefix(service)) and job.status in [
+            JobStatus.CREATED,
+            JobStatus.RUNNING,
+        ]:
+            result.append(job)
+    return result
+
+
+def is_something_queued_for(service: Service) -> bool:
+    return len(get_jobs_by_service(service)) != 0
 
 
 def add_backup_job(service: Service) -> Job:
+    if is_something_queued_for(service):
+        message = (
+            f"Cannot start a backup of {service.get_id()}, another operation is queued: "
+            + get_jobs_by_service(service)[0].type_id
+        )
+        raise ValueError(message)
     display_name = service.get_display_name()
     job = Jobs.add(
         type_id=backup_job_type(service),