Begin versioning Assigner configs

- Add schemas for versions 0, 1, and 2
- Schema validation
- Upgrading configs from one version to the next

Author: LinuxMercedes

assigner/config.py

@@ -0,0 +1,57 @@
+import logging
+import yaml
+
+from collections import UserDict
+
+from assigner.config.versions import upgrade, validate, ValidationError
+
+class DuplicateUserError(Exception):
+    pass
+
+def config_context(func):
+    def wrapper(cmdargs, *args):
+        with Config(cmdargs.config) as conf:
+            return func(conf, cmdargs, *args)
+    return wrapper
+
+
+class Config(UserDict):
+    """Context manager for config; automatically saves changes"""
+
+    def __init__(self, filename):
+        super().__init__()
+        self._filename = filename
+
+        try:
+            with open(filename) as f:
+                self.data = yaml.safe_load(f)
+        except FileNotFoundError:
+            pass  # Just make an empty config; create on __exit__()
+
+        try:
+            self.data = upgrade(self.data)
+            validate(self.data)
+        except ValidationError as e:
+            logging.warning("Your configuration is not valid: %s", e.message)
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, *args):
+        with open(self._filename, "w") as f:
+            yaml.dump(self.data, f, indent=2, default_flow_style=False)
+
+        return False  # propagate exceptions from the calling context
+
+    def __getattr__(self, key):
+        attr = getattr(super(Config, self), key, None)
+        if attr:
+            return attr
+        # Keys contained dashes can be called using an underscore
+        key = key.replace("_", "-")
+
+        # Fill in a blank roster if needed
+        if key == "roster" and self.data.get(key, None) is None:
+            self.data[key] = []
+
+        return self.data[key]