Attempt to backup archive before saving

After saving clean up the backup file if it exists.

csp_billing_adapter_local/plugin.py

@@ -22,6 +22,7 @@
 import logging
 import urllib.request
 import urllib.error
+import shutil
 
 from json.decoder import JSONDecodeError
 from pathlib import Path
@@ -100,9 +101,22 @@ def update_cache(config: Config, cache: dict, replace: bool):
 @csp_billing_adapter.hookimpl(trylast=True)
 def save_metering_archive(config: Config, archive_data: list):
     """Update local storage archive with new content"""
-    with open(get_local_path(ARCHIVE_FILE), 'w', encoding='utf-8') as f:
+    archive_path = get_local_path(ARCHIVE_FILE)
+    archive_bak = Path(str(archive_path) + '.bak')
+
+    try:
+        shutil.copy(archive_path, archive_bak)
+    except FileNotFoundError:
+        pass
+
+    with open(archive_path, 'w', encoding='utf-8') as f:
         json.dump(archive_data, f)
 
+    try:
+        archive_bak.unlink()
+    except FileNotFoundError:
+        pass
+
 
 @csp_billing_adapter.hookimpl(trylast=True)
 def get_metering_archive(config: Config):

tests/unit/test_plugin.py

@@ -26,7 +26,7 @@
 import json
 import logging
 from pathlib import Path
-from tempfile import NamedTemporaryFile
+from tempfile import NamedTemporaryFile, TemporaryDirectory
 from unittest.mock import patch
 from pytest import raises
 
@@ -477,8 +477,10 @@ def test_local_get_metering_archive_file_not_found_exception(
     def test_local_save_metering_archive(self, mock_get_local_path):
         """Test save_metering_archive() in local plugin"""
 
-        with NamedTemporaryFile() as temp_file:
-            mock_get_local_path.return_value = Path(temp_file.name)
+        with TemporaryDirectory() as temp_dir:
+            mock_get_local_path.return_value = Path(
+                temp_dir
+            ).joinpath('archive.json')
             archive = [{
                 'billing_time': '2024-02-09T18:11:59.527064+00:00',
                 'billing_status': {