Simplify domain traversal logic

This commit simplifies how directories are identified and traversed when
`domain.init()` is called. Most importantly, we no longer load a module
if it has been loaded already.

src/protean/domain/__init__.py

@@ -217,11 +217,19 @@ def _traverse(self):
         import os
         import pathlib
 
+        # Directory containing the domain file
         root_dir = pathlib.PurePath(pathlib.Path(self.root_path).resolve()).parent
-        path = pathlib.Path(root_dir)  # Resolve the domain file's directory
-        system_folder_path = (
-            path.parent
-        )  # Get the directory of the domain file to traverse from
+
+        # Parent Directory of the directory containing the domain file
+        #
+        #   We need this to decipher paths from the root. For example,
+        #   say the domain file is in a directory called `test13`, and
+        #   we are traversing a subdirectory `auth` inside `test13`.
+        #   We need to resolve the module for files in the `auth` directory
+        #   as `test13.auth`.
+        #
+        # This makes relative imports possible
+        system_folder_path = pathlib.Path(root_dir).parent
 
         logger.debug(f"Loading domain from {root_dir}...")
 
@@ -233,8 +241,9 @@ def _traverse(self):
             and name not in ["__pycache__"]
         ]
 
+        directories_to_traverse = [str(root_dir)]  # Include root directory
+
         # Identify subdirectories that have a toml file
-        subdirectories_to_traverse = []
         files_to_check = ["domain.toml", ".domain.toml", "pyproject.toml"]
         for subdirectory in subdirectories:
             subdirectory_path = os.path.join(root_dir, subdirectory)
@@ -243,59 +252,38 @@ def _traverse(self):
                 for file in files_to_check
                 if os.path.isfile(os.path.join(subdirectory_path, file))
             ):
-                subdirectories_to_traverse.append(subdirectory_path)
-
-        # Traverse root directory
-        for filename in os.listdir(root_dir):
-            full_file_path = os.path.join(root_dir, filename)
-            if (
-                os.path.isfile(full_file_path)
-                and os.path.splitext(filename)[1] == ".py"
-                and full_file_path != self.root_path
-            ):
-                spec = importlib.util.spec_from_file_location(
-                    filename, os.path.join(root_dir, filename)
-                )
-                module = importlib.util.module_from_spec(spec)
-                spec.loader.exec_module(module)
-
-                logger.debug(f"Loaded {filename}")
-
-        # Traverse subdirectories recursively
-        for directory in subdirectories_to_traverse:
-            for root, _, files in os.walk(directory):
-                if pathlib.PurePath(root).name not in ["__pycache__"]:
-                    package_path = root[len(str(system_folder_path)) + 1 :]
-                    module_name = package_path.replace(os.sep, ".")
-
-                    for file in files:
-                        file_base_name = os.path.basename(file)
-
-                        # Ignore if the file is not a python file
-                        if os.path.splitext(file_base_name)[1] != ".py":
-                            continue
-
-                        # Construct the module path to import from
-                        if file_base_name != "__init__":
-                            sub_module_name = os.path.splitext(file_base_name)[0]
-                            file_module_name = module_name + "." + sub_module_name
-                        else:
-                            file_module_name = module_name
-                        full_file_path = os.path.join(root, file)
-
-                        try:
-                            if (
-                                full_file_path != self.root_path
-                            ):  # Don't load the domain file itself again
-                                spec = importlib.util.spec_from_file_location(
-                                    file_module_name, full_file_path
-                                )
-                                module = importlib.util.module_from_spec(spec)
-                                spec.loader.exec_module(module)
+                directories_to_traverse.append(subdirectory_path)
+
+        # Traverse directories one by one
+        for directory in directories_to_traverse:
+            for filename in os.listdir(directory):
+                package_path = directory[len(str(system_folder_path)) + 1 :]
+                module_name = package_path.replace(os.sep, ".")
+                full_file_path = os.path.join(directory, filename)
+
+                if (
+                    os.path.isfile(full_file_path)
+                    and os.path.splitext(filename)[1] == ".py"
+                    and full_file_path != self.root_path
+                ):
+                    # Construct the module path to import from
+                    if filename != "__init__.py":
+                        sub_module_name = os.path.splitext(filename)[0]
+                        file_module_name = module_name + "." + sub_module_name
+                    else:
+                        file_module_name = module_name
+                    full_file_path = os.path.join(root_dir, filename)
+
+                    spec = importlib.util.spec_from_file_location(
+                        file_module_name, os.path.join(directory, filename)
+                    )
+                    module = importlib.util.module_from_spec(spec)
+
+                    # Do not load module again if it has already been loaded
+                    if module.__name__ not in sys.modules:
+                        spec.loader.exec_module(module)
 
-                                logger.debug(f"Loaded {file_module_name}")
-                        except ModuleNotFoundError as exc:
-                            logger.error(f"Error while loading a module: {exc}")
+                    logger.debug(f"Loaded {filename}")
 
     def _initialize(self):
         """Initialize domain dependencies and adapters."""