Add config.load function for loading config container

Document/lint config module
Add constants module

keyosk/config/__init__.py

@@ -1,7 +1,14 @@
+"""Application configuration settings containers and loading functions"""
+import os
 from dataclasses import dataclass
+from pathlib import Path
+from typing import Optional
+from typing import Union
 
 import marshmallow as msh
+import toml
 
+from keyosk import constants
 from keyosk.config.storage import KeyoskStorageConfig
 from keyosk.config.storage import StorageConfigSerializer
 
@@ -21,3 +28,29 @@ class ConfigSerializer(msh.Schema):
     """
 
     storage = msh.fields.Nested(StorageConfigSerializer)
+
+
+def load(source: Optional[Union[str, Path]] = None) -> KeyoskConfig:
+    """Load the configuration data
+
+    :param source: Optional path to the configuration file to load
+
+    The configuration file path can be found from one of the three follow places, listed
+    in the order of priority:
+
+    1. Parameter passed directly to this function
+    2. Environment variable specified by ``constants.ENV_CONFIG_PATH``
+    3. The default location, specified by ``constants.DEFAULT_CONFIG_PATH``
+    """
+
+    source = Path(
+        source or os.getenv(constants.ENV_CONFIG_PATH, constants.DEFAULT_CONFIG_PATH)
+    )
+
+    if source.exists():
+        with source.open() as infile:
+            data = toml.load(infile)
+    else:
+        data = {}
+
+    return ConfigSerializer().load(data)

keyosk/config/storage.py

@@ -1,3 +1,4 @@
+"""Data containers and utilities related to the storage configuration"""
 from dataclasses import asdict
 from dataclasses import dataclass
 from dataclasses import field
@@ -51,6 +52,8 @@ class SQLiteStorageConfigSerializer(msh.Schema):
     path = custom_fields.Path()
     pragmas = msh.fields.Dict(keys=msh.fields.String(), values=msh.fields.Raw())
 
+    # pylint: disable=unused-argument,no-self-use
+
     @msh.post_load
     def _make_dataclass(self, data: Mapping[str, Any], *args, **kwargs):
         return KeyoskSQLiteStorageConfig(**data)
@@ -101,6 +104,8 @@ class MariaStorageConfigSerializer(msh.Schema):
     username = msh.fields.String()
     password = msh.fields.String(allow_none=True)
 
+    # pylint: disable=unused-argument,no-self-use
+
     @msh.post_load
     def _make_dataclass(self, data: Mapping[str, Any], *args, **kwargs):
         return KeyoskMariaStorageConfig(**data)
@@ -142,6 +147,8 @@ class StorageConfigSerializer(msh.Schema):
     sqlite = msh.fields.Nested(SQLiteStorageConfigSerializer)
     maria = msh.fields.Nested(MariaStorageConfigSerializer)
 
+    # pylint: disable=unused-argument,no-self-use
+
     @msh.post_load
     def _make_dataclass(self, data: Mapping[str, Any], *args, **kwargs):
         return KeyoskStorageConfig(**data)

keyosk/constants.py

@@ -0,0 +1,3 @@
+DEFAULT_CONFIG_PATH = "/etc/keyosk/conf.toml"
+
+ENV_CONFIG_PATH = "KYSK_CONF_PATH"