Implement settings singleton

src/compub/settings.py

@@ -0,0 +1,113 @@
+import logging
+import logging.config
+from pathlib import Path
+from typing import Any, Callable, ClassVar
+
+from pydantic import BaseModel, BaseSettings, AnyUrl, validator
+from pydantic.env_settings import SettingsSourceCallable
+from yaml import safe_load
+
+
+log = logging.getLogger(__name__)
+
+
+PROGRAM_NAME = 'compub'
+
+THIS_DIR = Path(__file__).parent
+PROJECT_DIR = THIS_DIR.parent.parent
+
+DEFAULT_CONFIG_FILE_NAME = 'config.yaml'
+DEFAULT_CONFIG_FILE_PATHS = [
+    Path('/etc', PROGRAM_NAME, DEFAULT_CONFIG_FILE_NAME),  # system directory
+    Path(PROJECT_DIR, DEFAULT_CONFIG_FILE_NAME),           # project directory
+    Path('.', DEFAULT_CONFIG_FILE_NAME),                   # working directory
+]
+
+CONFIG_FILE_PATH_PARAM = 'config_file'
+
+
+class AbstractBaseSettings(BaseSettings):
+    _config_file_paths: ClassVar[list[Path]] = DEFAULT_CONFIG_FILE_PATHS
+
+    def __init__(self, *args, **kwargs):
+        config_file_path = kwargs.pop(CONFIG_FILE_PATH_PARAM, None)
+        if config_file_path is not None:
+            self._config_file_paths.append(Path(config_file_path))
+        super().__init__(*args, **kwargs)
+
+    def get_config_file_paths(self) -> list[Path]:
+        return self._config_file_paths
+
+    class Config:
+        allow_mutation = False
+        env_file_encoding = 'utf-8'
+        underscore_attrs_are_private = True
+
+        @classmethod
+        def customise_sources(
+                cls,
+                init_settings: SettingsSourceCallable,
+                env_settings: SettingsSourceCallable,
+                file_secret_settings: SettingsSourceCallable
+        ) -> tuple[Callable, ...]:
+            return init_settings, env_settings, _yaml_config_settings_source
+
+
+def _yaml_config_settings_source(settings_obj: AbstractBaseSettings) -> dict[str, Any]:
+    """
+    Incrementally loads (and updates) settings from all config files that can be found as returned by the
+    `Settings.get_config_file_paths` method and returns the result in a dictionary.
+    This function is intended to be used as a settings source in the `Config.customise_sources` method.
+    """
+    config = {}
+    for path in settings_obj.get_config_file_paths():
+        if not path.is_file():
+            log.debug(f"No config file found at '{path}'")
+            continue
+        log.info(f"Reading config file '{path}'")
+        with open(path, 'r') as f:
+            config.update(safe_load(f))
+    return config
+
+
+class DBUri(AnyUrl):
+    host_required = False
+
+
+class ServerSettings(BaseModel):
+    host: str = '127.0.0.1'
+    port: int = 9009
+    uds: str | None = None
+
+
+class Settings(AbstractBaseSettings):
+    db_uri: DBUri | None = None
+    server: ServerSettings = ServerSettings()
+    log_config: dict | Path | None = None
+
+    @validator('log_config')
+    def configure_logging(cls, v: dict | Path | None) -> dict | None:
+        if v is None:
+            return None
+        if isinstance(v, Path):
+            with open(v, 'r') as f:
+                logging_conf = safe_load(f)
+            logging.config.dictConfig(logging_conf)
+            return logging_conf
+        if isinstance(v, dict):
+            logging.config.dictConfig(v)
+            return v
+        raise TypeError
+
+
+settings = Settings()
+
+
+def init(**kwargs) -> None:
+    settings.__init__(**kwargs)
+
+
+def update(**kwargs) -> None:
+    settings_dict = settings.dict()
+    settings_dict.update(kwargs)
+    settings.__init__(**settings_dict)