json_data: Autorepair corrupted project files

If a file is detected as having corrupted unicode escapes, we make
a backup copy as filename.osp.bak (or filename.osp.bak.1...), then
regexp-replace all of the broken escapes with corrected ones. Then
we run the file through json.loads() and json.dumps() again to remove
the escaped characters, and write the results back to the original
file location as UTF-8.

src/classes/json_data.py

@@ -36,6 +36,7 @@
 from classes.assets import get_assets_path
 from classes.logger import log
 from classes import info
+from classes.app import get_app
 
 # Compiled path regex
 path_regex = re.compile(r'\"(image|path)\":.*?\"(.*?)\"')
@@ -53,6 +54,24 @@ def __init__(self):
         self._data = {}  # Private data store, accessible through the get and set methods
         self.data_type = "json data"
 
+        # Regular expression for project files with possible corruption
+        self.version_re = re.compile(r'"openshot-qt".*"2.5.0')
+
+        # Regular expression matching likely corruption in project files
+        self.damage_re = re.compile(r'/u([0-9a-fA-F]{4})')
+
+        # Connection to Qt main window, used in recovery alerts
+        app = get_app()
+        if app:
+            self.app = app
+
+        if app and app._tr:
+            self._ = app._tr
+        else:
+            def fn(arg):
+                return arg
+            self._ = fn
+
     def get(self, key):
         """ Get copied value of a given key in data store """
         key = key.lower()
@@ -108,7 +127,7 @@ def merge_settings(self, default, user):
             # Update default values to match user values
             for item in default:
                 user_value = user_values.get(item["setting"], None)
-                if user_value != None:
+                if user_value is not None:
                     item["value"] = user_value
 
             # Return merged list
@@ -129,16 +148,51 @@ def read_from_file(self, file_path, path_mode="ignore"):
         try:
             with open(file_path, 'r', encoding='utf-8') as f:
                 contents = f.read()
-                if contents:
-                    if path_mode == "absolute":
-                        # Convert any paths to absolute
-                        contents = self.convert_paths_to_absolute(file_path, contents)
-                    return json.loads(contents)
+            if not contents:
+                raise RuntimeError("Couldn't load {} file, no data.".format(self.data_type))
+
+            # Scan for and correct possible OpenShot 2.5.0 corruption
+            if self.damage_re.search(contents) and self.version_re.search(contents):
+                # File contains corruptions, backup and repair
+                self.make_repair_backup(file_path, contents)
+
+                # Repair all corrupted escapes
+                contents, subs_count = self.damage_re.subn(r'\\u\1', contents)
+
+                if subs_count < 1:
+                    # Nothing to do!
+                    log.info("No recovery substitutions on {}".format(file_path))
+                else:
+                    # We have to de- and re-serialize the data, to complete repairs
+                    temp_data = json.loads(contents)
+                    contents = json.dumps(temp_data, ensure_ascii=False)
+                    temp_data = {}
+
+                    # Save the repaired data back to the original file
+                    with open(file_path, "w", encoding="utf-8") as fout:
+                        fout.write(contents)
+
+                    msg_log = "Repaired {} corruptions in file {}"
+                    msg_local = self._("Repaired {num} corruptions in file {path}")
+                    log.info(msg_log.format(subs_count, file_path))
+                    if hasattr(self.app, "window") and hasattr(self.app.window, "statusBar"):
+                        self.app.window.statusBar.showMessage(
+                            msg_local.format(num=subs_count, path=file_path), 5000
+                        )
+
+            # Process JSON data
+            if path_mode == "absolute":
+                # Convert any paths to absolute
+                contents = self.convert_paths_to_absolute(file_path, contents)
+            return json.loads(contents)
+        except RuntimeError as ex:
+            log.error(str(ex))
+            raise
         except Exception as ex:
             msg = ("Couldn't load {} file: {}".format(self.data_type, ex))
             log.error(msg)
-            raise Exception(msg)
-        msg = ("Couldn't load {} file, no data.".format(self.data_type))
+            raise Exception(msg) from ex
+        msg = ()
         log.warning(msg)
         raise Exception(msg)
 
@@ -261,3 +315,42 @@ def convert_paths_to_relative(self, file_path, previous_path, data):
             log.error("Error while converting absolute paths to relative paths: %s" % str(ex))
 
         return data
+
+    def make_repair_backup(self, file_path, jsondata, backup_dir=None):
+        """ Make a backup copy of an OSP file before performing recovery """
+
+        if backup_dir:
+            backup_base = os.path.join(backup_dir, os.path.basename(file_path))
+        else:
+            backup_base = os.path.realpath(file_path)
+
+        # Generate a filename.osp.bak (or filename.osp.bak.1...) backup file name
+        backup_file = "{}.bak".format(backup_base)
+        dup_count = 1
+        while os.path.exists(backup_file) and dup_count <= 999:
+            backup_file = "{}.bak.{}".format(backup_base, dup_count)
+            dup_count += 1
+
+        if dup_count >= 1000:
+            # Something's wrong, we can't find a free save file name; bail
+            raise Exception("Aborting recovery, cannot create backup file")
+
+        # Attempt to open backup file for writing and store original data
+        try:
+            with open(backup_file, "w") as fout:
+                fout.write(jsondata)
+
+            if hasattr(self.app, "window") and hasattr(self.app.window, "statusBar"):
+                self.app.window.statusBar.showMessage(
+                    self._("Saved backup file {}").format(backup_file), 5000
+                )
+            log.info("Backed up {} as {}".format(file_path, backup_file))
+        except (PermissionError, FileExistsError) as ex:
+            # Couldn't write to backup file! Try alternate location
+            log.error("Couldn't write to backup file {}: {}".format(backup_file, ex))
+            if not backup_dir:
+                # Retry in alternate location
+                log.info("Attempting to save backup in user config directory")
+                self.make_repair_backup(file_path, jsondata, backup_dir=info.USER_PATH)
+            else:
+                raise Exception("Aborting recovery, cannot write backup file") from ex