Channels config file now has version information and set up basis for converting to newer versions

ChannelsConfigFile/ChannelsConfigFile.py

@@ -1,19 +1,37 @@
-from pathlib import Path
-from typing import Union, Dict, List
-import logging
-import json
 import atexit
+import json
+import logging
+from pathlib import Path
+from typing import Union, Dict, List, Callable, Tuple
+
 import discord
 
 import utils
+from . import vNoneTov1_0
 
 logger = logging.getLogger(__name__)
 
+# Functions used to convert between configuration versions, in a dictionary of: old_version -> converter
+# Each converter takes the old configuration and returns the converted configuration and the new version
+config_version_converters: Dict[Union[None, str], Callable[[Dict], Tuple[Dict, str]]] = {
+	None: vNoneTov1_0.convert
+}
+
 
 class ChannelsConfigFile:
 	"""
 	Wrapper for the channels configuration file, telling which channels to watch and which channels were created by the bot.
 	"""
+	version = "1.0"
+
+	@staticmethod
+	def empty_config() -> Dict:
+		"""
+		:return: An empty configuration, used to initialise the configuration file
+		"""
+		return {
+			"__version__": ChannelsConfigFile.version,
+		}
 
 	def __init__(self, config_file_path: Union[str, Path]):
 		self.config_file = None  # File descriptor to the on-disk config file
@@ -30,13 +48,15 @@ class ChannelsConfigFile:
 
 			if config_file_path.stat().st_size == 0:  # Config file is empty
 				logger.warning(f"Config file {config_file_path} is empty, using empty config")
-				self.config = {}
+				self.config = self.empty_config()
 				self.save_to_file()  # So that the file is proper json
 			else:  # Config file is not empty
-				self.reload_from_disk()
+				has_been_converted = self.reload_from_disk()
+				if has_been_converted:
+					self.save_to_file()
 		else:  # Config file does not exist
 			self.config_file = config_file_path.open("w+")
-			self.config = {}
+			self.config = self.empty_config()
 			self.save_to_file()  # So that the file is proper json
 
 		# Verifying that attributes have been initialised properly
@@ -45,9 +65,13 @@ class ChannelsConfigFile:
 
 		atexit.register(self.save_to_file)
 
-	def reload_from_disk(self) -> None:
+	def reload_from_disk(self) -> bool:
 		"""
 		Reload the configuration from the on-disk file
+
+		:return: Whether the configuration had to be converted to a more recent version because the on-file was an earlier version
+		:except json.JSONDecodeError: if the file is not valid json
+		:except ValueError: if the version of the configuration in the file is not known or can not be converted to a more recent one
 		"""
 		logger.debug("Loading channels configuration file from disk")
 		self.config_file.seek(0)  # Moving to beginning of file
@@ -56,7 +80,27 @@ class ChannelsConfigFile:
 		except json.JSONDecodeError as e:
 			logger.critical(f"JSON Error when parsing channels config file: {e}")
 			raise e
+		# Checking configuration version and converting if needed
+		config_version = self.config["__version__"] if "__version__" in self.config else None
+		has_been_converted = False
+		if config_version != self.version:
+			logger.info(f"Channels configuration file is an older version, converting (on-file: {config_version}, current: {self.version})...")
+
+			# Performing the conversion
+			while config_version != self.version:
+				if config_version in config_version_converters:
+					logger.debug(f"Converting from {config_version}")
+					self.config, config_version = config_version_converters[config_version](self.config)
+					logger.debug(f"Converted to {config_version}")
+				else:
+					logger.critical(f"Impossible to find converter to convert from {config_version}")
+					raise ValueError(f"Configuration loading: impossible to convert on-file config to current version")
+			has_been_converted = True
+
+		assert self.config["__version__"] == self.version
+
 		logger.debug("Loaded channels configuration file from disk")
+		return has_been_converted
 
 	def save_to_file(self, indent = 2) -> None:
 		"""

ChannelsConfigFile/vNoneTov1_0.py

@@ -0,0 +1,13 @@
+"""
+Converter for converting ChannelsConfigFile from version "Versions weren't a thing back then" to version 1.0
+"""
+
+from typing import Dict, Tuple
+
+
+def convert(config: Dict) -> Tuple[Dict, str]:
+	assert "__version__" not in config
+	# This first simple converter only adds version information to the config
+	# this poses the basis for version conversion
+	config["__version__"] = "1.0"
+	return config, "1.0"