Refactor code structure for improved readability and maintainability

.venv_codegen/Lib/site-packages/blackd/middlewares.py

@@ -0,0 +1,45 @@
+from collections.abc import Awaitable, Callable, Collection, Iterable
+
+from aiohttp import web
+from aiohttp.typedefs import Middleware
+from aiohttp.web_middlewares import middleware
+from aiohttp.web_request import Request
+from aiohttp.web_response import StreamResponse
+
+Handler = Callable[[Request], Awaitable[StreamResponse]]
+
+
+def cors(
+    *,
+    allow_headers: Iterable[str],
+    allow_origins: Collection[str],
+    expose_headers: Iterable[str],
+) -> Middleware:
+    @middleware
+    async def impl(request: Request, handler: Handler) -> StreamResponse:
+        origin = request.headers.get("Origin")
+        if not origin:
+            return await handler(request)
+
+        if origin not in allow_origins:
+            return web.Response(status=403, text="CORS origin is not allowed")
+
+        is_options = request.method == "OPTIONS"
+        is_preflight = is_options and "Access-Control-Request-Method" in request.headers
+        if is_preflight:
+            resp = StreamResponse()
+        else:
+            resp = await handler(request)
+
+        resp.headers["Access-Control-Allow-Origin"] = origin
+        if expose_headers:
+            resp.headers["Access-Control-Expose-Headers"] = ", ".join(expose_headers)
+        if is_options:
+            resp.headers["Access-Control-Allow-Headers"] = ", ".join(allow_headers)
+            resp.headers["Access-Control-Allow-Methods"] = ", ".join(
+                ("OPTIONS", "POST")
+            )
+
+        return resp
+
+    return impl