Add checks to determine whether "create" and "modify" can safely run

src/web/BL_Python/web/scaffolding/scaffolder.py

@@ -1,5 +1,8 @@
 import logging
+import sys
+import types
 from dataclasses import asdict, dataclass, field
+from importlib.machinery import SourceFileLoader
 from importlib.util import module_from_spec, spec_from_file_location
 from pathlib import Path
 from typing import Any, cast
@@ -313,7 +316,83 @@ def _scaffold_endpoints(
                 overwrite_existing_files=overwrite_existing_files,
             )
 
+    # it is safe for create if:
+    #      - the current directory is not a scaffolded application
+    # it is safe for modify if:
+    #      - the <application name> directory exists
+    #      - the <application name> directory is a scaffolded application
+    #      - the scaffolder is run from the scaffolded application's parent directory
+    def _check_scaffolded_application_exists(self, test_path: Path):
+        """
+        Determine whether the application <config.application_name> is an importable
+        BL_Python.web application that has been previously scaffolded with
+        this tool.
+
+        :param test_path: The directory to test for the existence of a scaffolded application.
+        """
+        application_import_path = Path(".", test_path)
+        self._log.debug(
+            f"Adding `{application_import_path}` to process module import path."
+        )
+        # modifying the import path to include a relative directory
+        # is less than ideal and potentionally dangerous. we should
+        # consider forking here or doing something else to prevent
+        # the global modification.
+        sys.path.insert(0, str(application_import_path))
+
+        try:
+            # if any of these steps fail, then the `test_path`
+            # does not already contain a scaffolded application
+            loader = SourceFileLoader(
+                self._config.application_name,
+                str(
+                    Path(
+                        test_path,
+                        self._config.application_name,
+                        "__init__.py",
+                    )
+                ),
+            )
+            mod = types.ModuleType(loader.name)
+            sys.modules[self._config.application_name] = mod
+            module = loader.load_module()
+            _ = module.__version__
+            _ = module._version.__bl_python_scaffold__
+            # if no errors occur, then the `test_path`
+            # contains a scaffolded application
+            return True
+        except Exception as e:
+            self._log.debug(str(e), exc_info=True)
+            return False
+        finally:
+            if self._config.application_name in sys.modules:
+                del sys.modules[self._config.application_name]
+            popped_import_path = sys.path.pop(0)
+            self._log.debug(
+                f"Popped `{popped_import_path}` from process module import path. Expected to pop `{application_import_path}`."
+            )
+
     def scaffold(self):
+        in_parent_directory = self._check_scaffolded_application_exists(
+            Path(self._config.output_directory)
+        )
+        in_application_directory = self._check_scaffolded_application_exists(Path("."))
+
+        # "create" can run from any directory that is not an existing
+        # application's root directory.
+        if self._config.mode == "create" and in_application_directory:
+            self._log.critical(
+                "Attmpted to scaffold a new application in the same directory as an existing application. This is not supported. Change your working directory to the application's parent directory, or run this from a directory that does not contain an existing application."
+            )
+            return
+        # modify can only run from an existing application's
+        # parent directory.
+        elif self._config.mode == "modify" and not in_parent_directory:
+            self._log.critical(
+                f"Attempted to modify an existing application from a directory that is not the existing application's parent directory. This is not supported. Change your working directory to the application's parent directory."
+            )
+            return
+
         # used for the primary set of templates that a
         # scaffolded application is made up of.
         base_env = Environment(

src/web/BL_Python/web/scaffolding/templates/base/{{application_name}}/__init__.py.j2

@@ -1,17 +1,20 @@
-application_configs = []
-application_modules = []
+from {{application_name}}._version import __version__
 
-{% if 'database' in module %}
-from BL_Python.database.config import DatabaseConfig
-from BL_Python.database.dependency_injection import ScopedSessionModule
-application_configs.append(DatabaseConfig)
-application_modules.append(ScopedSessionModule())
-{% endif %}
+def create_app():
+    application_configs = []
+    application_modules = []
 
-from BL_Python.web.application import create_app
-# fmt: off
-app = create_app(
-    application_configs=application_configs,
-    application_modules=application_modules
-)
-# fmt: on
+    {% if 'database' in module %}
+    from BL_Python.database.config import DatabaseConfig
+    from BL_Python.database.dependency_injection import ScopedSessionModule
+    application_configs.append(DatabaseConfig)
+    application_modules.append(ScopedSessionModule())
+    {% endif %}
+
+    from BL_Python.web.application import create_app as _create_app
+    # fmt: off
+    return _create_app(
+        application_configs=application_configs,
+        application_modules=application_modules
+    )
+    # fmt: on

src/web/BL_Python/web/scaffolding/templates/base/{{application_name}}/__main__.py.j2

@@ -1,3 +1,4 @@
-from __init__ import app
+from __init__ import create_app
 
-app.run()
+if __name__ == '__main__':
+    create_app().run()

src/web/BL_Python/web/scaffolding/templates/base/{{application_name}}/_version.py.j2

@@ -0,0 +1,4 @@
+import importlib.metadata
+
+__version__ = importlib.metadata.version(__package__ or __name__)
+__bl_python_scaffold__ = True