Initialise the application and update some module imports

1 files changed, 65 insertions, 0 deletions

diff --git a/gn_auth/__init__.py b/gn_auth/__init__.py
index e69de29..4ef2892 100644
--- a/gn_auth/__init__.py
+++ b/gn_auth/__init__.py
@@ -0,0 +1,65 @@
+import os
+import sys
+import logging
+
+from flask import Flask
+
+from . import settings
+
+class ConfigurationError(Exception):
+    """Raised in case of a configuration error."""
+
+def __check_secret_key__(app: Flask) -> None:
+    """Verify secret key is not empty."""
+    if app.config.get("SECRET_KEY", "") == "":
+        raise ConfigurationError("The `SECRET_KEY` settings cannot be empty.")
+
+def check_mandatory_settings(app: Flask) -> None:
+    """Verify that mandatory settings are defined in the application"""
+    undefined = tuple(
+        setting for setting in (
+            "SECRET_KEY", "SQL_URI", "AUTH_DB", "AUTH_MIGRATIONS",
+            "OAUTH2_SCOPE")
+        if setting not in app.config)
+    if len(undefined) > 0:
+        raise ConfigurationError(
+            "You must provide values for the following settings: " +
+            "\t* " + "\n\t* ".join(undefined))
+
+    __check_secret_key__(app)
+
+def override_settings_with_envvars(
+        app: Flask, ignore: tuple[str, ...]=tuple()) -> None:
+    """Override settings in `app` with those in ENVVARS"""
+    for setting in (key for key in app.config if key not in ignore):
+        app.config[setting] = os.environ.get(setting) or app.config[setting]
+
+def setup_logging_handlers(app: Flask) -> None:
+    """Setup the loggging handlers."""
+    stderr_handler = logging.StreamHandler(stream=sys.stderr)
+    app.logger.addHandler(stderr_handler)
+
+    root_logger = logging.getLogger()
+    root_logger.addHandler(stderr_handler)
+    root_logger.setLevel(app.config["LOGLEVEL"])
+
+def create_app(config: dict = {}) -> Flask:
+    """Create and return a new flask application."""
+    app = Flask(__name__)
+
+    # ====== Setup configuration ======
+    app.config.from_object(settings) # Default settings
+    # Override defaults with startup settings
+    app.config.update(config)
+    # Override app settings with site-local settings
+    if "GN_AUTH_CONF" in os.environ:
+        app.config.from_envvar("GN_AUTH_CONF")
+
+    override_settings_with_envvars(app)
+    # ====== END: Setup configuration ======
+
+    check_mandatory_settings(app)
+
+    setup_logging_handlers(app)
+
+    return app