Add db backup task

Close #2

src/meal_manager/scripts.py

@@ -1,13 +1,36 @@
 import argparse
 import datetime
+import os
+import shutil
+from pathlib import Path
 
-from sqlalchemy import Date, cast, func, select
+from sqlalchemy import func, select
 from sqlalchemy.orm import Session
 
-from meal_manager.main import engine
+from meal_manager.main import engine, sqlite_file_name
 from meal_manager.models import Event, Registration, Subscription
 
 
+def backup_db():
+    backup_dir = Path(os.environ.get("MEAL_MANAGER_BACKUP_DIR", None))
+    shutil.copy2(
+        sqlite_file_name,
+        backup_dir / f"{sqlite_file_name}.{datetime.datetime.now().isoformat()}",
+    )
+    # TODO: Delete old backups
+
+
+def run_nightly_tasks():
+    print("Applying Subscriptions")
+    with Session(engine) as session:
+        apply_subscriptions(session)
+
+    print("Running db backup")
+    backup_db()
+
+    print("Done running nightly tasks.")
+
+
 def apply_subscriptions(session: Session, event: Event = None, dry_run: bool = False):
 
     subscriptions = session.scalars(select(Subscription)).all()