Refactor Blueprint.register to reduce cyclomatic complexity

src/flask/sansio/blueprints.py

@@ -275,43 +275,13 @@ def register(self, app: App, options: dict[str, t.Any]) -> None:
         views and callbacks registered on the blueprint with the
         application. Creates a :class:`.BlueprintSetupState` and calls
         each :meth:`record` callback with it.
-
-        :param app: The application this blueprint is being registered
-            with.
-        :param options: Keyword arguments forwarded from
-            :meth:`~Flask.register_blueprint`.
-
-        .. versionchanged:: 2.3
-            Nested blueprints now correctly apply subdomains.
-
-        .. versionchanged:: 2.1
-            Registering the same blueprint with the same name multiple
-            times is an error.
-
-        .. versionchanged:: 2.0.1
-            Nested blueprints are registered with their dotted name.
-            This allows different blueprints with the same name to be
-            nested at different locations.
-
-        .. versionchanged:: 2.0.1
-            The ``name`` option can be used to change the (pre-dotted)
-            name the blueprint is registered with. This allows the same
-            blueprint to be registered multiple times with unique names
-            for ``url_for``.
+        ...
         """
         name_prefix = options.get("name_prefix", "")
         self_name = options.get("name", self.name)
         name = f"{name_prefix}.{self_name}".lstrip(".")
 
-        if name in app.blueprints:
-            bp_desc = "this" if app.blueprints[name] is self else "a different"
-            existing_at = f" '{name}'" if self_name != name else ""
-
-            raise ValueError(
-                f"The name '{self_name}' is already registered for"
-                f" {bp_desc} blueprint{existing_at}. Use 'name=' to"
-                f" provide a unique name."
-            )
+        self._ensure_unique_name(app, self_name, name)
 
         first_bp_registration = not any(bp is self for bp in app.blueprints.values())
         first_name_registration = name not in app.blueprints
@@ -320,61 +290,117 @@ def register(self, app: App, options: dict[str, t.Any]) -> None:
         self._got_registered_once = True
         state = self.make_setup_state(app, options, first_bp_registration)
 
-        if self.has_static_folder:
-            state.add_url_rule(
-                f"{self.static_url_path}/<path:filename>",
-                view_func=self.send_static_file,  # type: ignore[attr-defined]
-                endpoint="static",
-            )
+        self._register_static(state)
+        self._merge_blueprint_funcs_if_needed(
+            app, name, first_bp_registration, first_name_registration
+        )
+        self._run_deferred_functions(state)
+        self._register_cli(app, name, options)
+        self._register_nested_blueprints(app, state, name)
 
-        # Merge blueprint data into parent.
+    def _ensure_unique_name(self, app: App, self_name: str, name: str) -> None:
+        if name not in app.blueprints:
+            return
+
+        bp_desc = "this" if app.blueprints[name] is self else "a different"
+        existing_at = f" '{name}'" if self_name != name else ""
+
+        raise ValueError(
+            f"The name '{self_name}' is already registered for"
+            f" {bp_desc} blueprint{existing_at}. Use 'name=' to"
+            f" provide a unique name."
+        )
+
+    def _register_static(self, state: BlueprintSetupState) -> None:
+        if not self.has_static_folder:
+            return
+
+        state.add_url_rule(
+            f"{self.static_url_path}/<path:filename>",
+            view_func=self.send_static_file,  # type: ignore[attr-defined]
+            endpoint="static",
+        )
+
+    def _merge_blueprint_funcs_if_needed(
+        self,
+        app: App,
+        name: str,
+        first_bp_registration: bool,
+        first_name_registration: bool,
+    ) -> None:
         if first_bp_registration or first_name_registration:
             self._merge_blueprint_funcs(app, name)
 
+    def _run_deferred_functions(self, state: BlueprintSetupState) -> None:
         for deferred in self.deferred_functions:
             deferred(state)
 
+    def _register_cli(self, app: App, name: str, options: dict[str, t.Any]) -> None:
+        if not self.cli.commands:
+            return
+
         cli_resolved_group = options.get("cli_group", self.cli_group)
 
-        if self.cli.commands:
-            if cli_resolved_group is None:
-                app.cli.commands.update(self.cli.commands)
-            elif cli_resolved_group is _sentinel:
-                self.cli.name = name
-                app.cli.add_command(self.cli)
-            else:
-                self.cli.name = cli_resolved_group
-                app.cli.add_command(self.cli)
+        if cli_resolved_group is None:
+            app.cli.commands.update(self.cli.commands)
+        elif cli_resolved_group is _sentinel:
+            self.cli.name = name
+            app.cli.add_command(self.cli)
+        else:
+            self.cli.name = cli_resolved_group
+            app.cli.add_command(self.cli)
 
+    def _register_nested_blueprints(
+        self,
+        app: App,
+        state: BlueprintSetupState,
+        name: str,
+    ) -> None:
         for blueprint, bp_options in self._blueprints:
-            bp_options = bp_options.copy()
-            bp_url_prefix = bp_options.get("url_prefix")
-            bp_subdomain = bp_options.get("subdomain")
-
-            if bp_subdomain is None:
-                bp_subdomain = blueprint.subdomain
-
-            if state.subdomain is not None and bp_subdomain is not None:
-                bp_options["subdomain"] = bp_subdomain + "." + state.subdomain
-            elif bp_subdomain is not None:
-                bp_options["subdomain"] = bp_subdomain
-            elif state.subdomain is not None:
-                bp_options["subdomain"] = state.subdomain
-
-            if bp_url_prefix is None:
-                bp_url_prefix = blueprint.url_prefix
-
-            if state.url_prefix is not None and bp_url_prefix is not None:
-                bp_options["url_prefix"] = (
-                    state.url_prefix.rstrip("/") + "/" + bp_url_prefix.lstrip("/")
-                )
-            elif bp_url_prefix is not None:
-                bp_options["url_prefix"] = bp_url_prefix
-            elif state.url_prefix is not None:
-                bp_options["url_prefix"] = state.url_prefix
-
-            bp_options["name_prefix"] = name
-            blueprint.register(app, bp_options)
+            merged_options = self._compute_nested_blueprint_options(
+                blueprint, state, bp_options, name
+            )
+            blueprint.register(app, merged_options)
+
+    def _compute_nested_blueprint_options(
+        self,
+        blueprint: Blueprint,
+        state: BlueprintSetupState,
+        bp_options: dict[str, t.Any],
+        name: str,
+    ) -> dict[str, t.Any]:
+        bp_options = bp_options.copy()
+        bp_options["name_prefix"] = name
+
+        # --- subdomain ---
+        bp_subdomain = bp_options.get("subdomain")
+
+        if bp_subdomain is None:
+            bp_subdomain = blueprint.subdomain
+
+        if state.subdomain is not None and bp_subdomain is not None:
+            bp_options["subdomain"] = bp_subdomain + "." + state.subdomain
+        elif bp_subdomain is not None:
+            bp_options["subdomain"] = bp_subdomain
+        elif state.subdomain is not None:
+            bp_options["subdomain"] = state.subdomain
+
+        # --- url_prefix ---
+        bp_url_prefix = bp_options.get("url_prefix")
+
+        if bp_url_prefix is None:
+            bp_url_prefix = blueprint.url_prefix
+
+        if state.url_prefix is not None and bp_url_prefix is not None:
+            bp_options["url_prefix"] = (
+                state.url_prefix.rstrip("/") + "/" + bp_url_prefix.lstrip("/")
+            )
+        elif bp_url_prefix is not None:
+            bp_options["url_prefix"] = bp_url_prefix
+        elif state.url_prefix is not None:
+            bp_options["url_prefix"] = state.url_prefix
+
+        return bp_options
 
     def _merge_blueprint_funcs(self, app: App, name: str) -> None:
         def extend(