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hassio-google-drive-backup/backup/file/jsonfilesaver.py

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+import json
+import os
+from backup.logger import getLogger
+from os.path import exists
+
+logger = getLogger(__name__)
+
+
+class JsonFileSaver:
+    """
+    The envrionment Home Assistant runs in is notorious for disk-related failures, often from running completely out of space and SD card corruption.
+    Both of these can leave the addon in a state where the files it need to run are either corrupted or empty.  This class attempts to mitigate that
+    by writing all config files twice, first to a backup file and then to the "real" file path. Then when reading it will check both locations to try
+    and find a copy of the file that isn't corrupted or deleted.
+    This avoids a number of common failures, namely:
+    - A power failure while writing a file can leave it empty or malformed.
+    - Overwriting a file while the disk is full can truncateit without writing the new data
+    - HD corruption cna make a file malformed, but its less likely to affect both files.
+    """
+    @classmethod
+    def _read(cls, path):
+        with open(path, "r") as f:
+            return json.load(f)
+
+    @classmethod
+    def read(cls, path):
+        try:
+            return JsonFileSaver._read(path)
+        except json.decoder.JSONDecodeError:
+            logger.error(f"The configuration file {path} had an invalid format.  This could be caused by hard drive corruption or an unstable power event.  We'll attempt to load from a backup file instead.")
+            backup = JsonFileSaver._backup_path(path)
+            if not exists(backup):
+                logger.error("Unable to locate a backup path")
+                raise
+            return JsonFileSaver._read(backup)
+        except FileNotFoundError:
+            logger.error(f"The configuration file {path} was not found.  This could be caused by hard drive corruption or an unstable power event.  We'll attempt to load from a backup file instead.")
+            backup = JsonFileSaver._backup_path(path)
+            if not exists(backup):
+                logger.error("Unable to locate a backup path")
+                raise
+            return JsonFileSaver._read(backup)
+
+    @classmethod
+    def _write(cls, path, data):
+        with open(path, "w") as f:
+            json.dump(data, f, indent=4)
+
+    @classmethod
+    def write(cls, path, data):
+        # Crete the backup (rcovery) file first.  This ensures its present if the subsequent write is corrupted. 
+        JsonFileSaver._write(JsonFileSaver._backup_path(path), data)
+        JsonFileSaver._write(path, data)
+
+    @classmethod
+    def exists(cls, path):
+        if exists(path):
+            return True
+        return exists(JsonFileSaver._backup_path(path))
+
+    @classmethod
+    def delete(sels, path):
+        if exists(JsonFileSaver._backup_path(path)):
+            os.remove(JsonFileSaver._backup_path(path))
+        if exists(path):
+            os.remove(path)
+
+    @classmethod
+    def _backup_path(cls, path):
+        return path + ".backup"
+