Refactor the code

src/charm.py

@@ -15,7 +15,7 @@
 from constants import FLASK_CONTAINER_NAME
 from databases import Databases
 from exceptions import CharmConfigInvalidError, PebbleNotReadyError
-from flask_app import FlaskApp
+from flask_app import restart_flask
 from observability import Observability
 from secret_storage import SecretStorage
 from webserver import GunicornWebserver
@@ -45,10 +45,9 @@ def __init__(self, *args: typing.Any) -> None:
             charm_state=self._charm_state,
             flask_container=self.unit.get_container(FLASK_CONTAINER_NAME),
         )
-        self._flask_app = FlaskApp(
+        self._databases = Databases(
             charm=self, charm_state=self._charm_state, webserver=self._webserver
         )
-        self._databases = Databases(charm=self, flask_app=self._flask_app)
         self._charm_state.database_uris = self._databases.get_uris()
         self._ingress = IngressPerAppRequirer(
             self,
@@ -71,16 +70,6 @@ def __init__(self, *args: typing.Any) -> None:
             self.on.secret_storage_relation_changed, self._on_secret_storage_relation_changed
         )
 
-    def _update_app_and_unit_status(self, status: ops.StatusBase) -> None:
-        """Update the application and unit status.
-
-        Args:
-            status: the desired application and unit status.
-        """
-        self.unit.status = status
-        if self.unit.is_leader():
-            self.app.status = status
-
     def container(self) -> ops.Container:
         """Get the flask application workload container controller.
 
@@ -103,7 +92,7 @@ def _on_config_changed(self, _event: ops.EventBase) -> None:
         Args:
             _event: the config-changed event that triggers this callback function.
         """
-        self._flask_app.restart_flask()
+        self._restart_flask()
 
     def _on_statsd_prometheus_exporter_pebble_ready(self, _event: ops.PebbleReadyEvent) -> None:
         """Handle the statsd-prometheus-exporter-pebble-ready event."""
@@ -145,15 +134,33 @@ def _on_rotate_secret_key_action(self, event: ops.ActionEvent) -> None:
             return
         self._secret_storage.reset_flask_secret_key()
         event.set_results({"status": "success"})
-        self._flask_app.restart_flask()
+        self._restart_flask()
 
     def _on_secret_storage_relation_changed(self, _event: ops.RelationEvent) -> None:
         """Handle the secret-storage-relation-changed event.
 
         Args:
             _event: the action event that triggers this callback.
         """
-        self._flask_app.restart_flask()
+        self._restart_flask()
+
+    def _update_app_and_unit_status(self, status: ops.StatusBase) -> None:
+        """Update the application and unit status.
+
+        Args:
+            status: the desired application and unit status.
+        """
+        self.unit.status = status
+        if self.unit.is_leader():
+            self.app.status = status
+
+    def _restart_flask(self) -> None:
+        """Restart or start the flask service if not started with the latest configuration."""
+        try:
+            restart_flask(charm=self, charm_state=self._charm_state, webserver=self._webserver)
+            self._update_app_and_unit_status(ops.ActiveStatus())
+        except CharmConfigInvalidError as exc:
+            self._update_app_and_unit_status(ops.BlockedStatus(exc.msg))
 
 
 if __name__ == "__main__":  # pragma: nocover

src/databases.py

@@ -11,8 +11,11 @@
 import yaml
 from charms.data_platform_libs.v0.data_interfaces import DatabaseRequires, DatabaseRequiresEvent
 
+from charm_state import CharmState
 from constants import FLASK_DATABASE_NAME, FLASK_SUPPORTED_DB_INTERFACES
-from flask_app import FlaskApp
+from exceptions import CharmConfigInvalidError
+from flask_app import restart_flask
+from webserver import GunicornWebserver
 
 logger = logging.getLogger(__name__)
 
@@ -27,17 +30,21 @@ class Databases(ops.Object):  # pylint: disable=too-few-public-methods
         _databases: A dict of DatabaseRequires to store relations
     """
 
-    def __init__(self, charm: ops.CharmBase, flask_app: FlaskApp):
+    def __init__(
+        self, charm: ops.CharmBase, charm_state: CharmState, webserver: GunicornWebserver
+    ):
         """Initialize a new instance of the Databases class.
 
         Args:
-            charm: The main charm. Used for events callbacks
-            flask_app: The flask application manager
+            charm: The main charm. Used for events callbacks.
+            charm_state: The charm's state.
+            webserver: The webserver manager object.
         """
         # The following is necessary to be able to subscribe to callbacks from ops.framework
         super().__init__(charm, "databases")
         self._charm = charm
-        self._flask_app = flask_app
+        self._charm_state = charm_state
+        self._webserver = webserver
 
         metadata = yaml.safe_load(pathlib.Path("metadata.yaml").read_text(encoding="utf-8"))
         self._db_interfaces = (
@@ -53,13 +60,33 @@ def __init__(self, charm: ops.CharmBase, flask_app: FlaskApp):
             for name in self._db_interfaces
         }
 
+    def _update_app_and_unit_status(self, status: ops.StatusBase) -> None:
+        """Update the application and unit status.
+
+        Args:
+            status: the desired application and unit status.
+        """
+        self._charm.unit.status = status
+        if self._charm.unit.is_leader():
+            self._charm.app.status = status
+
+    def _restart_flask(self) -> None:
+        """Restart or start the flask service if not started with the latest configuration."""
+        try:
+            restart_flask(
+                charm=self._charm, charm_state=self._charm_state, webserver=self._webserver
+            )
+            self._update_app_and_unit_status(ops.ActiveStatus())
+        except CharmConfigInvalidError as exc:
+            self._update_app_and_unit_status(ops.BlockedStatus(exc.msg))
+
     def _on_database_requires_event(self, _event: DatabaseRequiresEvent) -> None:
         """Configure the flask pebble service layer in case of DatabaseRequiresEvent.
 
         Args:
             _event: the database-requires-changed event that trigger this callback function.
         """
-        self._flask_app.restart_flask()
+        self._restart_flask()
 
     def _setup_database_requirer(self, relation_name: str, database_name: str) -> DatabaseRequires:
         """Set up a DatabaseRequires instance.

src/flask_app.py

@@ -10,111 +10,96 @@
 
 from charm_state import KNOWN_CHARM_CONFIG, CharmState
 from constants import FLASK_ENV_CONFIG_PREFIX, FLASK_SERVICE_NAME
-from exceptions import CharmConfigInvalidError
 from webserver import GunicornWebserver
 
 logger = logging.getLogger(__name__)
 
 
-class FlaskApp:  # pylint: disable=too-few-public-methods
-    """A class representing the Flask application."""
-
-    def __init__(
-        self, charm: ops.CharmBase, charm_state: CharmState, webserver: GunicornWebserver
-    ):
-        """Initialize a new instance of the FlaskApp class.
-
-        Args:
-            charm: The main charm object.
-            charm_state: The state of the charm that the FlaskApp instance belongs to.
-            webserver: The webserver manager object.
-        """
-        self._charm = charm
-        self._charm_state = charm_state
-        self._webserver = webserver
-
-    def _flask_environment(self) -> dict[str, str]:
-        """Generate a Flask environment dictionary from the charm Flask configurations.
-
-        The Flask environment generation follows these rules:
-            1. User-defined configuration cannot overwrite built-in Flask configurations, even if
-                the built-in Flask configuration value is None (undefined).
-            2. Boolean and integer-typed configuration values will be JSON encoded before
-                being passed to Flask.
-            3. String-typed configuration values will be passed to Flask as environment variables
-                directly.
-
-        Returns:
-            A dictionary representing the Flask environment variables.
-        """
-        builtin_flask_config = [
-            c.removeprefix("flask_") for c in KNOWN_CHARM_CONFIG if c.startswith("flask_")
-        ]
-        flask_env = {
-            k: v for k, v in self._charm_state.app_config.items() if k not in builtin_flask_config
-        }
-        flask_env.update(self._charm_state.flask_config)
-        env = {
-            f"{FLASK_ENV_CONFIG_PREFIX}{k.upper()}": v if isinstance(v, str) else json.dumps(v)
-            for k, v in flask_env.items()
-        }
-        secret_key_env = f"{FLASK_ENV_CONFIG_PREFIX}SECRET_KEY"
-        if secret_key_env not in env:
-            env[secret_key_env] = self._charm_state.flask_secret_key
-        for proxy_variable in ("http_proxy", "https_proxy", "no_proxy"):
-            proxy_value = getattr(self._charm_state.proxy, proxy_variable)
-            if proxy_value:
-                env[proxy_variable] = str(proxy_value)
-                env[proxy_variable.upper()] = str(proxy_value)
-        env.update(self._charm_state.database_uris)
-        return env
-
-    def _flask_layer(self) -> ops.pebble.LayerDict:
-        """Generate the pebble layer definition for flask application.
-
-        Returns:
-            The pebble layer definition for flask application.
-        """
-        environment = self._flask_environment()
-        return ops.pebble.LayerDict(
-            services={
-                FLASK_SERVICE_NAME: {
-                    "override": "replace",
-                    "summary": "Flask application service",
-                    "command": shlex.join(self._webserver.command),
-                    "startup": "enabled",
-                    "environment": environment,
-                }
-            },
-        )
-
-    def _update_app_and_unit_status(self, status: ops.StatusBase) -> None:
-        """Update the application and unit status.
-
-        Args:
-            status: the desired application and unit status.
-        """
-        self._charm.unit.status = status
-        if self._charm.unit.is_leader():
-            self._charm.app.status = status
-
-    def restart_flask(self) -> None:
-        """Restart or start the flask service if not started with the latest configuration."""
-        container = self._charm.unit.get_container("flask-app")
-        if not container.can_connect():
-            logger.info("pebble client in the Flask container is not ready")
-            return
-        if not self._charm_state.is_secret_storage_ready:
-            logger.info("secret storage is not initialized")
-            return
-        container.add_layer("flask-app", self._flask_layer(), combine=True)
-        is_webserver_running = container.get_service(FLASK_SERVICE_NAME).is_running()
-        try:
-            self._webserver.update_config(
-                flask_environment=self._flask_environment(),
-                is_webserver_running=is_webserver_running,
-            )
-        except CharmConfigInvalidError as exc:
-            self._update_app_and_unit_status(ops.BlockedStatus(exc.msg))
-        container.replan()
-        self._update_app_and_unit_status(ops.ActiveStatus())
+def _flask_environment(charm_state: CharmState) -> dict[str, str]:
+    """Generate a Flask environment dictionary from the charm Flask configurations.
+
+    Args:
+        charm_state: The state of the charm.
+
+    The Flask environment generation follows these rules:
+        1. User-defined configuration cannot overwrite built-in Flask configurations, even if
+            the built-in Flask configuration value is None (undefined).
+        2. Boolean and integer-typed configuration values will be JSON encoded before
+            being passed to Flask.
+        3. String-typed configuration values will be passed to Flask as environment variables
+            directly.
+
+    Returns:
+        A dictionary representing the Flask environment variables.
+    """
+    builtin_flask_config = [
+        c.removeprefix("flask_") for c in KNOWN_CHARM_CONFIG if c.startswith("flask_")
+    ]
+    flask_env = {k: v for k, v in charm_state.app_config.items() if k not in builtin_flask_config}
+    flask_env.update(charm_state.flask_config)
+    env = {
+        f"{FLASK_ENV_CONFIG_PREFIX}{k.upper()}": v if isinstance(v, str) else json.dumps(v)
+        for k, v in flask_env.items()
+    }
+    secret_key_env = f"{FLASK_ENV_CONFIG_PREFIX}SECRET_KEY"
+    if secret_key_env not in env:
+        env[secret_key_env] = charm_state.flask_secret_key
+    for proxy_variable in ("http_proxy", "https_proxy", "no_proxy"):
+        proxy_value = getattr(charm_state.proxy, proxy_variable)
+        if proxy_value:
+            env[proxy_variable] = str(proxy_value)
+            env[proxy_variable.upper()] = str(proxy_value)
+    env.update(charm_state.database_uris)
+    return env
+
+
+def _flask_layer(charm_state: CharmState, webserver: GunicornWebserver) -> ops.pebble.LayerDict:
+    """Generate the pebble layer definition for flask application.
+
+    Args:
+        charm_state: The state of the charm
+        webserver: The webserver manager object
+
+    Returns:
+        The pebble layer definition for flask application.
+    """
+    environment = _flask_environment(charm_state=charm_state)
+    return ops.pebble.LayerDict(
+        services={
+            FLASK_SERVICE_NAME: {
+                "override": "replace",
+                "summary": "Flask application service",
+                "command": shlex.join(webserver.command),
+                "startup": "enabled",
+                "environment": environment,
+            }
+        },
+    )
+
+
+def restart_flask(
+    charm: ops.CharmBase, charm_state: CharmState, webserver: GunicornWebserver
+) -> None:
+    """Restart or start the flask service if not started with the latest configuration.
+
+    Raise CharmConfigInvalidError if the configuration is not valid.
+
+    Args:
+        charm: The main charm object.
+        charm_state: The state of the charm.
+        webserver: The webserver manager object.
+    """
+    container = charm.unit.get_container("flask-app")
+    if not container.can_connect():
+        logger.info("pebble client in the Flask container is not ready")
+        return
+    if not charm_state.is_secret_storage_ready:
+        logger.info("secret storage is not initialized")
+        return
+    container.add_layer("flask-app", _flask_layer(charm_state, webserver), combine=True)
+    is_webserver_running = container.get_service(FLASK_SERVICE_NAME).is_running()
+    webserver.update_config(
+        flask_environment=_flask_environment(charm_state),
+        is_webserver_running=is_webserver_running,
+    )
+    container.replan()

tests/unit/test_charm.py

@@ -13,7 +13,7 @@
 
 from charm_state import KNOWN_CHARM_CONFIG, CharmState
 from constants import FLASK_CONTAINER_NAME
-from flask_app import FlaskApp
+from flask_app import restart_flask
 from webserver import GunicornWebserver
 
 FLASK_BASE_DIR = "/srv/flask"
@@ -34,8 +34,7 @@ def test_flask_pebble_layer(harness: Harness) -> None:
         charm_state=charm_state,
         flask_container=harness.charm.unit.get_container(FLASK_CONTAINER_NAME),
     )
-    flask_app = FlaskApp(charm=harness.charm, charm_state=charm_state, webserver=webserver)
-    flask_app.restart_flask()
+    restart_flask(charm=harness.charm, charm_state=charm_state, webserver=webserver)
     flask_layer = harness.get_container_pebble_plan("flask-app").to_dict()["services"]["flask-app"]
     assert flask_layer == {
         "override": "replace",

tests/unit/test_databases.py

@@ -96,7 +96,9 @@ def test_database_uri_mocked(
     send_signal_mock = unittest.mock.MagicMock()
     monkeypatch.setattr(container, "send_signal", send_signal_mock)
 
-    databases = Databases(unittest.mock.MagicMock(), unittest.mock.MagicMock())
+    databases = Databases(
+        unittest.mock.MagicMock(), unittest.mock.MagicMock(), unittest.mock.MagicMock()
+    )
     assert not databases.get_uris()
 
     # Create the databases mock with the relation data